Congenital mirror movements · JournalofNeurology,Neurosurgery,andPsychiatry, 1981. 44, 586-599...

Journal of Neurology, Neurosurgery, and Psychiatry, 1981. 44, 586-599

Congenital mirror movementsG D SCHOTT AND MARIA A WYKE

From the National Hospitals for Nervous Diseases, Queen Square and Maida Vale, London

S UMM AR Y In this report are described seven patients assessed clinically and neuropsycho-logically in whom mirror movements affecting predominantly the hands occurred as a congenitaldisorder. These mirror movements, representing a specific type of abnormal synkinesia, mayarise as a hereditary condition, in the presence of a recognisable underlying neurological ab-normality, and sporadically, and the seven patients provide more or less satisfactory examplesof each of these three groups. Despite the apparent uniformity of the disorder, the heterogeneityand variability may be marked, examples in some of our patients including the pronouncedincrease in tone that developed with arm movement, and the capacity for modulation of theassociated movement by alteration of neck position and bio-feedback. Various possible mech-anisms are considered; these include impaired cerebral inhibition of unwanted movements, andfunctioning of abnormal motor pathways. Emphasis has been placed on the putative role of thedirect, crossed corticomotoneurone pathways and on the unilateral and bilateral cerebral eventsthat precede movement.

Of the many forms of associated movements,mirror movements are those characterised by in-voluntary movements executed by one side of thebody which are mirror reversals with respect tothe intended movements. The term "mirror move-ment" appears first to have been used byBauman,' probably being derived from an analogywith mirror writing.2 3 Certain mirror movementssuch as smiling and blinking are obvious in every-day life; they are also features of normal child-hood motor function, as seen in the symmetricalMoro response and in the posturing of the armsthat can be observed in children at around thefifth month of life.4From the various types of pathological mirror

movements, a particular group can be delineatedwhich has the following characteristics: pre-dominant or exclusive involvement of the hands,partial suppressibility, increase in the associatedmovement with effort, and lack of progressionafter childhood. We have classified this conditionof obligatory bimanual associated movements intothree groups: (1) that occurring as a hereditarydisorder, usually with an autosomal dominantpattern of inheritance, (2) that occurring in the

Address for reprint requests: Dr GD Schott, The National Hospitalfor Nervous Diseases, Queen Square, London WCIN 3BG.Accepted 18 May 1981

presence of a neurological disorder-either con-genital or acquired, and (3) that occurring spor-adically in otherwise normal individuals.5 In thispaper, we wish to confine our observations topatients whose mirror movements date fromearly childhood and in whom therefore thephenomenon appears to be congenital.

In 1977, we observed a 15-year-old otherwisehealthy boy, who had throughout life shown in-voluntary mirror movements of the limbs. Atthat time it appeared that the movements heexecuted were similar to the apparently uniformdescriptions of previous cases reported in theliterature. Since then, we have been able to studysix further patients who represent more or lesssatisfactory examples from each of the threegroups referred to above. The purpose of thepresent report, in which these patients are pre-sented together with a resume of our earlier case,is to draw attention to the hitherto unrecognisedheterogeneity of the clinical features and to con-sider afresh possible mechanisms that may sub-serve these rare bimanual synkinesias.

Patients and methods

The case histories of the patients are given below, andsummarised in tables 1 and 2. Patients were investi-

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Table 1 Summary of clinical features

Case Sex Age (yr) Condition Investigations

GROUP l-FamilialI JG M 39 ? Recessive inheritance Normal

GROUP 2-Congenital underlying disorder2 DH M 41 Agenesis of corpus callosum CT scan-features of agenesis of corpus callosum3 CW F 34 Klippel-Feil syndrome Radiographs-large foramen magnum, blocks of fused cervical

vertebrae; myelogram-wide cervical canal, posterior arachnoidpouches

4 SA F 31 Usher's syndrome Abnormal electro-oculogram and electro-retinogram; audiogram-severe sensorineural deafness and loudness recruitment

5 SK F 17 Unidentified cranio-cervical anomaly Radiographs-spina bifida occulta of Cl, fused neural arches ofCl and 2, fused bodies of C5 and 6. (Normal myelogram)

6 LE F 30 Multiple cervical and thoracic Radiographs-malformed bodies and arches of C6 and 7, archesspinal anomalies of D2-5, and right 3rd and 6th and left 2nd, 3rd and 4th ribs

GROUP 3-Sporadic7 DC M 15 Normal Normal

Table 2 Mirror movements

Case Involvement Amplitude Mirror movements Alteration Other featureson passive movement in tone

1 JG hands+ + arms+ L=R - + + + Partially suppressible with bio-feedback2 DH hands ++ arms+ L>R -

eyes+ mouth+3 CW hands+ + arms+ R>L - - Movements influenced by neck position4 SA hands+ + arms+ L=R - -

eyes+5SK hands++toes± R>L - - Clumsyrighthand6 LE hands+ + eyes+ L=R - + + Partially suppressible with bio-feedback

toes+7DC hands++arms+ R>L +

legs+ toes+

gated with radiographs of the skull and spine, com-puted tomography (CT) of the head, electroencephal-ography (EEG), and spinal and cortical sensory evokedpotentials6 recorded over the ipsilateral and contra-lateral scalp. The last tWo investigations were normalin all patients; abnormalities detected and the resultsof additional abnormal investigations are included intable 1. The patients were also given a neuropsycho-logical evaluation which included a handednessquestionnaire,7 tests of intelligence (WAIS), and testsof motor proficiency (cutting with scissors, maze trac-ing, placing coins and matchsticks in a box, anddrawing lines) taken from the Oseretsky Scale;8 psy-chomotor skills were evaluated using tests of rapidityof movemen'ts9 and the Perdue Dexterity Test.'0 Theresults are sutnmarised in table 3.

In assessing the movements, each hand was testedindependently and observations made concerning thedirection of the associated mbvement (that is mirroror homologous, see reference 5). Most of the associ-ated movements were mirror forms of the intendedmovements, but at times they were less easy tocharacterise-as indicated in the case histories below.When writing simultaneously with both hands, fourpatients produced occasional and fragmentary mirror

Table 3 Neuropsychological AssessmentCase Handedness Full scale Psychomotor performance

IQ (WAIS)

1 JG Right 131 Normal2 DH Predominantly 72 Low normal

right3 CW Right 102 Normal4 SA Right 48 Clumsy and slow5 SK Left 75 Clumsy and slow6 LE Right 114 Normal7 DC Left 83 Normal

writing, but no definite mirror writing could be seenwhen wtiting with the preferred hand alone. Thepatients were also asked to perform "complementary"bimanual movements, that is tasks which requiredthe simultaneous use of the two hands, as in windingthread onto a spool and threading a nut onto a bolt.In no patient was any associated or interfering move-ment noted.Two patients (JG and LE) attempted to control the

involuntary movements using bio-feedback. The tech-nique employed EMG feedback from the extensormuscles of the forearm showing the associated move-ment; feedback was both auditory using a tone of

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varying pitch and visual using a calibrated meter.TIhese patients were able to suppress the involuntarymovements for a few minutes after continuous train-ing for periods lasting up to 20 minutes. One patient(JG) was able to control the involuntary movementsof both the left and right hands; the other (LE) couldonly control the movements of the preferred hand.Additional investigations were carried out on patientDH (agenesis of the corpus callosum) in order to assess

possible impairment of inter-hemispheric transfer ofinformation." The assessment disclosed no such im-pairment; for instance, with eyes closed, objectsactively explored with one hand could be recognisedby the other.

Case histories

Case 1, JGThis 39-year-old consultant for an electronics firmfirst recalled "clumsiness" of the hands when playingwith mechanical toys as a child. He was aware ofhaving difficulty carrying out intricate manoeuvres

and his fingers appeared to move clumsily. By theage of 8 years he recalled that his two hands in-voluntarily tended to move simultaneously. At theage of 14 years he started to learn to play the piano,and whilst his problems probably did not progress,they became more obtrusive and the bimanual move-ments seriously interfered with this activity. As hebecame older, he became aware that many or mostof the movements performed with one hand werefaithfully copied in mirror fashion by the other-for example, putting his hand in his pocket, writingand turning knobs. Finger and wrist movements weremainly affected with slight involvement of the fore-arms. Other than an irnability to play the piano, therehad been no interference with everyday activities in-cluding sport. The amplitude of the movements mayhave increased during childhood and were enhancedby stress and anxiety, but he had always partly beenable to suppress the unwanted activity, albeit witheffort, and this appeared to impose a "strain" on

both arms. It is possible that he involuntarily usedthis increase in tone in an attempt to control themirrored movements. The face and legs were un-

involved.He learnt to write at around the age of 4 years,

talked well at 3 and walked at 18 months. Hisgeneral health remained excellent. His only sibling,a brother, also exhibited mirror movements althoughunfortunately details remain anecdotal since hedied aged 27 years in an accident. Throughout lifehe had had difficulty in manipulating fine objectson account of "stiffness" and "clumsiness" of thefingers, and he showed non-progressive but verymarked mirror movements affecting both hands. Hisparents and other relatives were unaffected and therewas no consanguinity.Examination of JG showed slight synkinetic move-

ment upwards of the ipsilateral corner of the mouthon closing each eye; on voluntarily closing each eye,

G D Schott and Maria A Wyke

particularly the left, some associated closure move-ments of the other eye also occurred. There wasneither motor nor sensory deficit in the limbs, thereflexes were normal, and tone at rest, co-ordinationand fine and discrete finger movements were alsonormal. On movements of one arm, however, andeven even on anticipation of movement, striking in-crease in tone in the opposite arm appeared, thishypertonicity appearing poorly localised in the oppositelimb. Discrete movements of the fingers of eitherhand produced mirror movements of the contralateralfingers, whether the movements were made individu-ally or in combination in more complex tasks such aswriting and manipulating fine objects. Mirroring alsooccurred on movement of the hand and wrist, and toa small extent on movement of the forearm and evenupper arm. The mirror movement was often less inamplitude than the in'tended one, and could be par-tially suppressed, usually being associated with furtherincrease in tone. All synkinetic movements were en-hanced when the intended movement was carried outwith effort. There was no n'oticeable asymmetry be-tween the two sides, passive movements did not causemirroring, and there was no abnormality of the legs.

Case 2, DHThis 41-year-old waiter had three brief epilepticseizures, and at that time mirror movements firstattracted medical attention. Enquiry, however, re-vealed that the patient had had mirror movements foras long as he could recall. As a chlild he rememberedhis mother encouraging him to sit on one hand to stopthe other hand moving. He was almost illiterate, andhad little recollection of making mirror movementswhen trying to write. Everyday tasks proved difficulton account of these movements: for instance liftinga teapot with one hand resulted in the other handbecom'ing lifted up and making gripping movements.Similar problems occurred holding jugs and beer mugs-a source of embarrassment in his occupation. Com-bing his hair resulted in similar movements of theother arm, also when he manipulated nuts and boltsand used a screwdriver. These fine, gripping andturning movements had been the most troublesome,especially when effort was required, whilst no prob-lems had been encountered with grosser movementssuch as hammering; he had been unable to controlhis symptoms voluntarily. There was a greater ten-dency for mirroring to occur in the left hand withintended movements of the righit, than vice versa.There had been no progression and his legs and facewere uninvolved. His previous and family historywere unremarkable.Examination was normal except for the presence

of mirror movements. These affected individualfinger movements-such as flexion and extension-and also more complex movements such as serial op-position of the thumb to each finger. There weresome mirror movements on opening and closing thefist, also seen with activities such as doing up buttons,turning knobs and winding a watch. On forceful



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movement against resistance, mirror movements affect-ing shoulder abduction and adduction and also elbowflexion and extension could be demonstrated; similarmirror movements could be brought out with grossarm movements, for instance when insctibing circlesin the air with the outstretched arm or even with thehand alone. When drawing in rungs of a ladder in acentrifugal direction, there resulted some slight mirrormovements of the contralateral hand, and with at-tempts at writing with either hand, some low ampli-tude involuntary movements were visible in thecontralateral hand. There was some asymmetry ofresponse, the right hand tending to mirror thosemovements mtade with the left hand to a lesserextent compared with when the right hand made theintended movement. In the face, whilst closure ofthe right eye caused associated closure of the lefteye, only slight associated movements of the righteye occurred when closing the left. Elevation of theleft corner of the mouth caused some elevation ofthe right side, whilst vice versa, more synkineticmovements occurred. The feet were unaffected. Toneremained normal throughout testing and passive move-ments did not cause synkinetic movements.

Case 3, CWThis 34-year-old lady was born with a short neck butremained asymptomatic until the age of 23 years.She then complained of episodes of tingling in theleft arm and leg, intermittent burning in the leftarm and slight impairment of grip of the left hand.Her family history was unremarkable. The findingson examination were similar to those currently ob-served. Although not having sought medical attentionfor this, mirror movements had been present for aslong as she could remember, and according to hermother had been present even during infancy. Thuswhen she had reached for an object with one hand,the other hand would make a similar movement. Thepatient remembered as a child mirror movementsoccurring, for instance when she did up buttons orturned knobs; in one instance, she recalled that whenscratching the side of her head with one hand, theother produced a curious partial mirrored movement.When aged 10 years, she tried to suppress the un-wanted movement, although suppression caused con-siderable and rather diffuse "strain" in the armshowing the mirror movements. Over the years, shehad unconsciously partly been able to control themovements, although certain activities she still findsdifficult-for instance plaiting her child's hair whichinvolves different but simultaneous activity of the twohands. Activities involving co-operative bimanualmovements-such as sewing or manipulating nuts andbolts, cause no difficulties. Affected movements aremainly those of the fingers and wrist; over the years,control has been executed predominantly over thethumb, index and middle fingers, and mirroring ineveryday life now particularly affects the little andring fingers. There is no asymmetry. Movements re-quiring effort such as undoing tight bottle tops or

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taps cause enhanced mirroring, and also a sense ofdiffuse strain mainly in the forearm muscles, as re-ferred to above. Forearm mirror movements particu-larly occur when she stirs a cooking pot. Certainactivities have proven more difficult: when writingshe has developed the habit of making a fist withthe left hand to prevent the unwanted movements.Some larger movements of the arm also tend tocause mirroring-for instance catching a ball. Learn-ing to play the piano had to be abandoned due to theconsiderable difficulties encountered, and as a nurse,she tended to drop a vial held in one hand, whenthe other hand was drawing-up fluid into a syringe.Examination revealed a very short neck with low

hair line, cervical kyphosis, restriction of all neckmovements to about 15 degrees, and webbing at theshoulders. There was first degree horizontal nystag-mus in both eyes on lateral gaze in either direct'ion;in the left arm, there was slight weakness affectingleft shoulder abduction and elbow, wrist and fingerextension. The arm reflexes were reduced bilaterally.There was neither sensory loss nor ataxia, and nosigns of a foramen magnum lesion or spinal cord in-volvement. There were obvious mirror movements ofthe fingers with particular involvement of the littleand ring fingers. The movements were not alwaysprecisely mirrored and symmetrical: particularlynoticeable was that movement of a finger of theright h-and tended to produce some diffuse synkineticmovements affecting at times several fingers of theleft hand. Mirroring affected wrist movements, andalso to a slight extent more gross movements of thewhole arm-such as when making circles in the airwith the outstretched arm. Usually the amplitude ofmirroring produced by the right hand was greater thanthat of the left. A striking finding was the increaseand slowing of the mirror movements with forwardflexion of the neck, at a time when there was noother demonstrable change in neurological function.Synkinetic movements of the face and legs were notseen.

Case 4, SAThis 31-year-old lady, the product of a pregnancycomplicated by antepartum haemorrhage, was bornuneventfully weighing 51b 10oz. Whilst the perinatalperiod was unremarkable, her developmental mile-stones were markedly delayed. She crawled at 9mon'ths, walked at 2 years, and was slow to talk: herspeech was almost unintelligible by the age of 5. At7 years she was noted to be deaf, and at 8 to bepartially sig'hted and bilateral cataracts were found.She had three grand mal seizures between the agesof 5 and 23 years. She had never been able to reador write and had attended special schools; for a timeshe mianaged a simple assembly job in a factory. Herfamily history was unremarkable and there was noparental consanguinity. Througout the patient's life,her mother had been aware of the presence of mirrormovements affecting the arms. The patient herselfwas able to recall few details of these movemen'ts



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although she did remember their occurrence whenshe turned knobs on a radio; the movements had notbeen progressive and caused no disability.On examination of this retarded girl, her visual

acuity was 6/60 in the right eye and 6/36 in the left,and there was tunnel vision, attenuated fundal vessels,retinal pigment epithelial degeneration and cataractsin both eyes. There was severe bilateral deafness. Inthe limbs there was neither weakness nor alterationin tone but slowness in executing fine finger and toemovements bilaterally. There was no ataxia. Sen-sation was normal, as were the tendon reflexes, andthe plantar responses were flexor. A diagnosis ofUsher's syndrome'2 13 had been made. The faceshowed no abnormal associated movements, exceptthat she was unable to close either eye independently.Mirror movements were evident in the upper limbsand especially the hands, and were particularly strik-ing on lateral finger movements and when morecomplicated tasks were undertaken such as sequentialopposition of the thumb to each finger. There was atendency for spread of discrete finger movements toinvolve adjacent fingers-for example, flexion of anindex finger often caused flexion of the adjacentthumb as well as mirror movements of both thesefingers of the opposite hand. Attempts at writingproduced some synkinetic movements of the fingersof the left hand. Slight mirroring also occurred proxi-mally, particularly in the forearms when rotationalmovements were made. The legs were uninvolved.There was no alteration in tone on executing armmovements nor with change in posture of the head.

Case 5, SKThis 17-year-old girl had had weak and clumsy handssince birth; there had been a suggestion of progressionin recent years, probably attributable to increasingawareness as she started employment. The symptomshad always predominantly affected the right arm,which she found difficult to elevate, and marked im-pairment in function of the right hand resulted inalmost exclusive use of the left. She had noticedlongstanding difficulty in carrying out fine tasks suchas writing, typing and in doing up and undoingbuttons. Born in India, she came to England at theage of 5 years, started school a year later and afterleaving at the age of 16, she took up work as a shopassistant. Her family history was unremarkable. Shehad been aware of mirror movements throughout life,although they caused her no concern. She had noticedsome asymmetry, with a greater tendency when usingthe left hand for the right hand to imitate movementsthan vice versa.Examination of this left handed girl revealed three

cafe-au-lait patches on the skin, and a small m'idlinepit in the back of the neck; the latter had apparentlybeen noted at birth. The cranial nerves were normal.There was slight thinning of the muscles of theshoulder girdle and small muscles of the hands,clawing of the fingers bilaterally but particularly theright, WVinging of the scapulae, and bilateral but


particularly right sided weakness of both deltoids andspinati, triceps, wrist and finger extensors and thesmall muscles of the hands. Movements of the handswere carried out slowly but there was neither ataxianor disturbance of tone. The legs were normal.Whilst the biceps and brachioradialis reflexes werewell preserved, the triceps and leg reflexes weresluggish; the abdominal responses were absent but theplantar responses flexor. Sensory testing revealedslightly impaired postural sense in the fingers bilater-ally. Mirror movements were also apparent. Activeuse of the left hand produced mirror movements ofthe right; thus tapping with a single finger, abductionof the fingers, and pill-rolleing movements of thefingers as well as gripping, pronation and supination ofthe wrist, and more complex tasks such as undoingtops and turning knobs all produced symmetricalmovements of the right side. Attempting these move-ments with the right hand produced less mirror move-ments of the left, and movements executed with theright hand frequently showed diffuse dispersal of themirror movements produced by the left hand. Shehad difficu'lty holding a pen, but writing with theleft hand produced marked mirror movements ofthe right. Mirroring was not detected proximally in theupper arms but there was a suggestion of occasional,slight and variable toe movements of the contralateralgreat and second toes when rapid flexion-extensionmovements of the toes of one foot were performed.

Case 6, LEThis 30-year-old-lady was born with a mis-shapen andshorter left foot and leg. This had caused little func-tional disability but she had come under medical careas a result of some local pain in that foot. Herfamily history was negative. Her parents had notedmirror movements since her birth, and as a youngchiild, she recalled that when waving to people in thestreet the other hand would make similar but lessmarked movements. As she learnt to write, she be-came aware of mirror movements of the left hand,and in particular releasing the grip of one handcaused similar release movements of the other. Num-erous activities were associated With mirror move-ments, including turning door knobs, sewing, using ascrewdriver and catching a ball. These movementsresulted in embarrassment rather than functionaldisability.

Examination revealed slight weakness of neckflexion, elevation of the right shoulder, flattening ofthe interscapular region, thoracic scoliosis and markedpes cavus deformity of the left foot. There was slightweakness of all movements of the left hand and arm,which although causing no functional impairment,she had been aware of throughout life. There wassevere weakness of left ankle dorsiflexion and eversionand also toe dorsiflexion. Sensory examination wasnormal. The arm reflexes were normal and sym-metrical, whilst the reflexes in the left leg wereexaggerated, the left plantar response was extensorand the left sided abdominal responses were reduced.



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Mirror movements were evident, and affected discreteand fine finger movements of both hands, oppositionmovements of the thumb to each finger, and abduc-tion and adduction movements of the fingers. Theupper arms were not affected. When either arm wasused, marked increase in tone occurred in the con-tralateral arm, but this was not so striking as in JG.There was no significant asymmetry. In the face,right eye closure was associated with involuntaryclosure of the left eye, whilst left eye closure wasaccompanied by only slight mirror movements of theright. There were some mirror movements of the toesof the right foot on flexion of the left toes. Passivemovements did not produce any mirror phenomena.

Case 7, DC (Resume from Schott and Wyke5)This 15-year-old boy had had involuntary mirrormovements since infancy, his parents noticing that atthe age of 3 years, picking up objects with one handwas associated with similar movements of the other.By the age of 7 years these movements were moreprominent and particularly affected gripping; themovements could only be suppressed partially andwere increased with effort. He found holding milkbottles in both hands was hazardous, since release ofone bottle caused release of the other, and later ropeclimbing, typewriting and piano playing had to beabandoned. The mirrored movements when writingcaused considerable embarrassment at school. Therehad been no progression over the years and medicaladvice was only sought because difficulty was antici-pated in the boy's aspirations to become a diamondcutter. The family history was unremarkable.Examination was normal except for the presence

of mirror movements, which spared the face. Indi-vidual finger movements and more complex move-ments of the hands produced mirror movements ofthe contralateral side, although the mirrored move-ments were more evident when the left hand wvascarrying out voluntary movements. Less mirroringoccurred on more proximal movements of the arms.Passive movements of the fingers and wrist, and pro-nation and supination of the forearm, especially whenabruptly executed, sometimes produced similarthough small amplitude mirror movements. In thelegs, slight mirror movements were detected on vol-untary movement of the toes or ankle. All associatedmovements were enhanced when active movement wasperformed against resistance.

Discussion

Although the term "mirror movements" is em-ployed to describe those involuntary movementsexecuted by one side of the body which aremirror reversals with respect to the intendedmovements, usage has tended to lead to a lessstrict application of the meaning of the term, andin many instances it is used to imply simultaneous

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and often bimanual movements which are notnecessarily strictly mirrored. Imitative, homo-logous, and corresponding are alternative and lessrestrictive terms sometimes used. 14 That thisaspect is not merely semantic becomes evidentwhen considering that different mechanisms mayhave to be invoked when considering explanationsfor these movements.

Interest in associated movements in general firstdeveloped during the 19th century (for historicalreview, see reference 14), but a century ago,Westphal15 delineated symmetrical synkineticmovements as a specific group amongst these in-voluntary movements. The normal mirror move-ments of children and adults have been referredto earlier, but pathological mirror movements par-ticularly affecting the hands are also seen both inchildren'0 and in adults in many acquired dis-orders of the nervous system, including cer-ebrovascular accidents,17 cerebral tumours,18 19

trauma,20 21 extrapyramidal disease22 23 and sub-arachnoid haemorrhage.24 In this report, however,we have confined ourselves to a consideration ofsome unusual patients whose bimanual mirrormovements are congenital, and in some of whoman underlying and relevant abnormality of thenervous system has been detected.

Despite different underlying disorders, the sevencases described here share the characteristicfeatures that have long been recognised in thiscondition: the movements affect solely or pre-dominantly the hands and especially the fingers,are present on active and rarely passive move-ments of one side, are noted during infancy andshow no significant progression, and are them-selves associated with no other functional deficitunless an underlying neurological disorder shouldcontribute additional handicaps. Often the mirrormovement is of a lesser amplitude than the in-tended one, and there is no doubt that some degreeof voluntary control can be exerted over theassociated movement. These associated movementsmay often be only a fragment of the voluntarymovement and sometimes do not even resembleit; this explains for instance why when writing,mirror writing is not inevitably produced by thenon-dominant hand, and also demonstrates thelack of precision of the term "mirror movements"when applied to these patients.The functional problems these movements cause

are usually insignificant; curiously, typewritingand playing the piano are often impossible,25whereas sewing, manipulating nuts and bolts, andother fine mechanical tasks appear to present fewdifficulties. It may be that this is because activities

c



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such as piano playing demand independent andseparate activity of the two hands, whilst many ofthe other tasks require independent yet bimanuallyco-ordinated ac'tivity. Other curious and predict-able problems have been noted-in one of ourpatients (Case 7) difficulties were encounteredwhen carrying bottles of milk in each hand, andthe problems encountered by the sailor attemptingto climb a rope can easily be envisaged.26 It isnoteworthy that only one of the seven cases des-cribed here came to medical attention on accountof these movements, which demonstrates the lackof both progression and of the development offurther neurological problems.Mirror movements have been investigated by

electromyograplhic (EMG) techniques for manyyears,27-30 but detailed reports of patients withcongenital mirror movements studied by currentEMG techniques are sparse. Regli, Filippa andWiesendanger31 analysed mirror movements intwo brothers: EMG investigation of rapid flexionmovement of the forearm revealed activity in thecontralateral arm with coactivation of the antag-onistic muscle pair. Whilst the latency of theactivity was often the same on the two sides, onaverage the latency of the mirror activity wasslightly longer, and Jelasic and Ott'9 reachedsimilar conclusions studying patients with mirrormovements who were otherwise normal. Baird,Robinson and Buckler32 studied mirror movementselectromyographically in patients with the Klippel-Feil syndrome; although the association betweenthe syndrome and mirror movements was highlysignificant, the presence of mirror movementscould not be correlated with any clinical or radio-logical features. Notermans, Go and Boonstra33have also studied mirror movements using EMGin a patient with the Klippel-Feil syndrome. Whilstof interest, these reports have contributed rela-tively little to an understanding of underlyingmechanisms, and when EMG studies were under-taken on our patient DC, we were impressed bythe great variability of the response evoked in thecontralateral muscles.

Despite the apparent uniformity of the clinicalfeatures, our cases demonstrate a heterogeneitybarely recognised in the literature on the subject.For instance, there was often asymmetry betweenthe movements of the two sides, in two of ourcases there was very pronounced increase in tonewhen the mirror movements were produced, inthree cases slight associated movements of thetoes could be observed, in one patient the move-ments were markedly affected by head posture,in another passive movements induced mirror


movements, and in four patients some associatedmovements of the eyelids or mouth were noted.The latter as with many other associated facialmovements34 are commonly found in otherwisenormal individuals and likely to be of little sig-nificance. As well as the various differences inthe clinical features, the underlying conditions insome patients include a number of more or lessidentifiable disorders, an aspect which needs to beaccoun'ted for when attempting to construct anyunifying hypothesis to explain these abnormalmovements.

CONSIDERATIONS OF UNDERLYING ABNORMALITIES

Abnormalities of the cervical spineThe commonest condition recorded in associationwith congenital mirror movements has been theKlippel-Feil syndrome, in which numerous associ-ated developmental defects such as Sprengel'sdeformity, platybasia, and extradural spinal massesmay occur, as also may defects of the cervicaland thoracic cord.35 Mirror movements were firstnoted in this congenital cervical spine abnormalityby Bauman,' who reported on their occurrence infour out of six cases, and although the associationhas been questioned,36 several other confirmatoryreports have subsequently appeared (see reference37). Mirror movements have also been describedin other congenital skeletal abnormalities of thecraniocervical region, such as the Arnold-Chiarimalformation and basilar impression.38 The pro-pensity for mirror movements to occur in theseconditions is unexplained. Of considerable im-portance are the pathological studies in two casesof the Klippel-Feil syndrome associated withmirror movements in which striking abnormalitiesof the cervical cord have been demonstrated. Inthe case described by Gunderson and Solitare,39apart from the apparent absence of pyramidal de-cussation with defects of cord fusion, the corpuscallosum was found to be abnormally thin. InAvery and Rentfro's40 case, there was nearly com-plete division posteriorly of the cervical and upperthoracic cord, but unfortunately the brain wasnot examined.A possible mechanism that has been considered

by many of these authors is that of impaired de-cussation of the pyramidal tracts, perhaps withconsequent use of alternative, less specific andbilateral pathways. In the present report, twopatients had unequivocal major skeletal abnor-malities of the cervical and upper thoracic spinewith a probable abnormality of the underlyingcord, and a further patient had clinical evidenceof a high cervical lesion with a congenital mid-



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line cutaneous abnormality-the underlying defectremaining unidentified. In some instances, mirrormovements may be inherited (see below) and itshould be recalled that certain abnormalities inthe region of the craniocervical junction maythemselves be inherited, including the Klippel-Feilsyndrome,41 basilar impression42 and the Arnold-Chiari malformation.43

A genesis of the corpus callosumWhether mirror movements take place via inter-hemispheric pathways has long been debated, butevidence on this is lacking. It is of interest, how-ever, that callosal section does not appear toprevent at least those mirror movements acquiredthrough trauma.44 The occurrence of these move-ments in agenesis of the corpus callosum hasattracted little attention even when noted." Ourobservation of a patient (Case 2) who presentedfortuitously, whose callosal agenesis would haveremained undetected without computed tom-ography and in whom no other neurological ab-normalities were encountered, raises the questionas to whether previously reported "normal" indi-viduals with mirror movements who were notinvestigated by such techniques, may have had anundetected abnormality of this kind. The associ-ation of the Klippel-Feil syndrome with an ab-normally thin corpus callosum has been referredto above. Also pertinent is the agenesis of thecorpus callosum detected in one member of afamily with mirror movements, mental retarda-tion and various skeletal abnormalities.45

Is it possible to link the two groups of patientsin whom an underlying defect can be demon-strated, that is those with abnormalities of thecorpus callosum and of the cervical spine andcord? Apart from the necropsy findings referredto above, agenesis of the corpus callosum is ac-companied by a remarkably high incidence ofassociated anatomical abnormalities, and particu-larly striking is the study by Parrish, Roessmannand Levinsohn46 in which six of 11 patients withagenesis of the corpus callosum were found tohave abnormalities involving the pyramidal sys-tem. In their review of the literature, associatedpyramidal tract abnormalities were reported insix of 47 other cases, which they considered to bean underestimate. It seems reasonable thereforeto suggest that as mirror movements may beassociated both with agenesis of the corpus callo-sum and with congenital cervical spine abnor-malities, and as there is a high incidence ofabnormalities of the pyramidal tracts in both dis-orders, abnormalities of these tracts may provide

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a common basis for the occurrence of mirrormovements.

In considering structural aspects, referenceshould be made to the apparently unrelated com-bination of mirror movements with hypogonado-tropic hypogonadism and anosmia. This triad hasrecently been reported as a familial disorder byConrad, Kriebel and Hetzel,37 and possible earlierexamples cited. These authors proposed that hypo-gonadism and anosmia (Kallman's syndrome) mayarise from a developmental dysraphic state-analogous to for example the Klippel-Feil syn-drome-and thus all the known structural dis-orders seen with mirror movements appear toshare a defect of midline structures, perhaps withattendant abnormalities of neural topography.

Mental retardationIt is well recognised that the bilateral associatedmovements which are a normal feature of infancyare more likely to persist in brain damaged chil-dren,47 48 and mirror writing is also more com-monly encountered among "defective" children.49Non-specific "brain damage" appears to allowmirror movements to persist indefinitely, and thiswas recognised by von Fragstein50 who commentedon these movements in "idiots"; the movementshave also been described in hereditary mentaldefectiveness,45 hereditary schizophrenia,5' and"phenylpyruvic oligophrenia".52 In our patientwith Usher's syndrome, mirror movements ap-peared in a setting of multiple congenital defectsof which mental retardation was one major mani-festation. There has been speculation that thedisappearance of normal mirror movements mightbe related to the development of a hypothetical"inhibitory" mec'hanism which would allowseparate, individual and non-mirror movements tooccur. This hypothesis, and the possibility thatinhibition may fail to develop in patients withmental retardation and aggression,53 are discussedlater.

FAMILIAL AND SPORADIC CASESIn these two groups, patients with congenitalmirror movements have no detectable abnormalityof the nervous system. The inclusion of our caseJG as an example of familial mirror movementsmust remain unsatisfactory, as we were unableto assess the reportedly affected brother. How-ever there seems no reason to doubt that bothbrothers were similarly affected, and we are awareof 18 reports of familial mirror movements affect-ing 86 individuals (see reference 37). The usualmode of inheritance is as an autosomal dominant,although Lackner54 described a family with a less



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well defined pattern of inheritance, and Rasmussenand Waldenstrom55 reported a patient with mirrormovements whose healthy parents were firstcousins and where an autosomal recessive modeof inheritance was postulated. It may be, there-fore, that there is heterogeneity amongst thefanmilial cases, although inheritance as an auto-somal dominant condition is the most common.Of particular interest in our case is the strikinghypertonicity developed by the limbs in thepresence of mirror movements; whether thischaracteristic is typical of familial cases is notknown, although it was a feature of one ofLackner's54 two cases.The familial incidence of a number of cranio-

cervical abnormalities in which mirror movementsmay occur has already been referred to, andthese abnormalities are usually inherited as auto-somal dominant conditions. Agenesis of the cor-pus callosum may also be inherited, and bothautosomal dominant and recessive patterns havebeen described.56 Whether there is a specificallyinherited abnormality of motor pathways is un-

known; it is of interest, however, that at least inthe peripheral nervous system, familial patterns ofanomalous innervation have been described, themode of inheritance again proebably being as an

autosomal dominant.57Since the first obscure description by Thomayer

in 1887,58 59 nine patients have been reported inwhom mirror movements occurred as a non-familial condition in the absence of any identifiableassociated neurological or skeletal abnormality.5 19It should be emphasised that in the majority ofthese cases which we have termed sporadic, nor-mality was assessed on clinical grounds. The case

(Patient 7) described by us and summarised abovehas been the only one in this group to have beeninvestigated by modern techniques, now a pre-

requisite for inclusion in the group of otherwisenormal individuals.

MECHANISMS OF CONGENITAL BIMANUAL MIRRORMOVEMENTS

All theories which attempt to explain these move-

ments must account for why the movements affectsolely or predominantly the hands and fingers,commence during early life and do not progress,

and may be partially suppressible. The theoriesshould also account for the fact that although thesame bimanual synkinetic movements normallyoccur in children and then disappear during thefirst or second decade,47 48 60 they may occasionallybe seen on extreme effort in healthy adults, andcan be demonstrated in normal people as sub-


clinical movements by various techniques, includ-ing plethysmographyll and EMG.27 62

Inhibitory mechanismsThose early theories concerning inhibition andreferred to above envisaged that with normalmatura'tion, an inhibitory centre or mechanismdevelops which allows individual, separate andnon-synkinetic movements to occur. There is someevidence for the presence of such a process. Forexample, left handers probably naturally write inmirror script from right to left, and it is edu-cation and cultural influences which tend to causeconventional script to supersede.63 Moreover,inhibition can apparently be overcome in righthanders, who when obligatorily taking up writingand other activities with their left hand, may thentransiently undertake mirror movements almostunaware.64 Thus it seems that inhibitory mech-anisms may be continuously active but are capableof being removed.There are two other aspects relevant to theories

of inhibition which require comment. First, con-cerning movement-related cortical potentials, ithas long been recognised that with unilateral handmovement, the first EEG activity prior to move-ment, the readiness potential or Bereitschafts-potential, is diffuse, bilateral and symmetrical, andthe last pre-motor potential to be recorded isrestricted to the contralateral hand area of themotor cortex (for references, see 65, 66). Theintervening potentials are currently being evalu-ated, and whilst controversial,62 these may includean ipsilateral pre-motion potential ("P1") whichit has been suggested may be related to inhibitoryactivity of ipsilateral pathways.67 Second, infor-mation obtained from vascular studies indicatesthat there is increased blood flow in both supple-mentary motor areas during the programming andexecution of individual finger movements, but in-creased regional blood flow in only the con-tralateral primary motor area.68 The parallel in-formation from these two different types of studyraises the question as to whether some form ofinhibition or modulation may be occurring be-tween early bilateral cerebral activity and latercontralateral cerebral activity-inhibition whichcould be abnormal in patients with mirrormovements.

Functional considerations also point to theseparation between diffuse bilateral and discretecontralateral cerebral activity. In man, at leastin respect of the limbs, focal stimulation of themotor cortex results in purely contralateral move-ments. This is evident in the normal subject



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with stimulation through the intact skull,09 inpatients with focal motor epilepsy, and at surgeryon the exposed cortex;70 indeed, Penfield andJasper70 state "bilateral representation of move-ment of either extremity does not exist in manas far as our experience of Rolandic stimulationgoes." (Unfortunately information at present islacking on the effect of percutaneous stimulationof the motor cortex in patients with mirror move-ments.) These abnormally-induced movementswhich follow direct stimulation of the motorcortex are, however, clearly different from thenormal, programmed and sometimes deliberatemovements presumably generated deeply, diffuselyand bilaterally and in which the supplementarymotor areas become activated; which if either ofthese mechanisms is pertinent to mirror move-ments remains unknown.These aspects leave unanswered why the ab-

normal movements affect the hands and fingers,usually in the absence of any defect of fine fingercontrol or discrete finger movement. Theories ofinhibition also need to explain the heterogeneity,variability, and partial suppressibility of the move-ments, and the effect of passive movements in in-ducing contralateral movements. Such passively-induced associated movements were present inone of our cases, and have been described in otherreports, for instance by Drinkwater7l and Gutt-man, Maclay and Stokes.72 Presumably focalafferent impulses trigger contralateral motor path-ways but there is no evidence, apart from thequestionable73 case reported by Drinkwater,7' ofallocheiria or any other phenomena affecting thesensory system in patients with mirror movements.The effect is presumably linked to localised sen-sory pathways since only the contralateral part isactivated following passive movement; the appli-cation of studies on cortical motor potentials fol-lowing both voluntary and passive finger move-ments74 to patients with mirror movements mayprove revealing.

Abnormal pathwaysA second major concept invoked has been that ofabnormal descending motor pathways. Abnormal-ities of the corpus callosum and of pyramidal de-cussation in the cervical region have been con-sidered above; other theories involving neuraltopography have also been considered, includinginhibition of bilateral cerebral representation.20loss of suppression of bilateral activity,75 impairedinhibitory function of the parietal lobe,2' 24 anduse of ipsilaterally projecting corticospinal path-ways.31 37 71 The case reported by Haerer and

595

Currier70 is of particular importance in this con-text. A patient with congenital and familial mirrormovements sustained a cerebral infarction leadingto a right hemiplegia; mirror movements persistedin the hand which'otherwise remained completelyflacc'id and paralysed. It seems unlikely that thesemovements could be due to activity of the lefthand motor cortex and Haerer and Currier postu-lated that the movements of the right hand aroseeither from the right (ipsilateral) cortex or distantsubcortical structures, and that mirror movementsin general might be caused by distribution ofcortical motor neurones from each hemisphere toeach "cervical cord hand area" in association withincomplete pyramidal decussation. It should beemphasised that the nature of anatomical abnor-malities in patients with mirror movements re-mains virtually unknown. It is difficult, however,to envisage how the variability of the movementscould occur in the presence of gross abnormalitiesor lesions affecting motor pathways, particularlywhen impairment of motor function rarely occurs.The relation between mirror movements andposition of the neck in our patient (case 3) is ofinterest, since it suggests a possible mechanicalfactor altering the function of motor pathwaysspecifically at that level.The complexity of the motor pathways needs no

emphasis. There is considerable anatomical vari-ation of these pathways in man,77 and of particularimportance is one of the conclusions reached fromNathan and Smith's78 later study: the lateralcorticospinal tract of each side has bilateral in-fluences. In the following section, some aspectsrelated to specific corticospinal pathways will beconsidered.

A hypothesis combining mechanisms of inhibitionand abnormal pathways?A satisfactory explanat'ion for congenital mirrormovements may lie in an abnormality affectingthe important direct, crossed corticomotoneuronepathways, w'hich-at least in primates-are nowfirmly established as being fairly specific for move-ments of the hands and in particular for theexecution of fine finger movements.79 80 Thesedirect and crossed pathways develop relatively lateand coincide with the acquisition of motor skills8'-both crucial aspects when explaining congenitalmirror movements. In those of our patients whosemirror movements arose in a setting of recognis-able abnormalities, a common factor might wellcomprise an abnormality of these specific path-ways. Consistent with the use of the direct corti-comotoneurone pathways is neuropsychological



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evidence, which also suggests that abductive move-ments-probably relevant for fine and individualfinger control-are subserved by the contralateralhemisphere and may be mediated by these crossedmotor neurones.82 An abnormality affecting, forinstance, decussation of these pathways in thebrain or cervical cord must however remainspeculative.

If the direct, crossed corticomotoneurone path-ways are implicated in mirror movements, can in-hibition of these pathways be demonstrated? Itis of interest that our patients were able to under-take everyday activities without difficulty whenthe two hands were employed together, and simi-larly we did not observe associated movements inany of our patients when both hands were usedco-operatively, which suggests that inhibition maybe occurring at least in these circumstances. Inthis respect the observations made by Jung andDietz85 are of relevance. They found that whilstthere was a unilateral prolongation of motorlatency in affected muscles of patients with dis-orders affecting one pyramidal pathway, this delayin initiation of voluntary movements disappearedwhen movements were made bilaterally. They con-sidered the best explanation was the use of ipsi-lateral projections of uncrossed pyramidal fibresto the motor neurones. Recalling that the readinesspotential and cerebral blood flow in the supple-mentary motor areas are bilateral, inhibition ofthese ipsilateral pathways perhaps usually occurs,the inhibition only being removed or circumventedby bilateral movements. There is some furtherevidence which might support this proposal.Mention has already been made of the contro-versial movement-related pre-motion potential("P1") which is ipsilateral to the voluntarily con-tracting muscles; of interest is the observationthat on bilateral movement of the thumb, Shi-basaki and Kato67 could not record this ipsilateralpotential, and they suggested that it might indeedbe related to inhibition of imitative (mirror)movements.The relevance of the alteration in tone noted in

two of our patients is uncertain. Whilst clinicaldisorders of the basal ganglia and cerebellum arenot typically accompanied by mirror movements,rormal movement is preceded by diffuse neuronalactivity in cerebellar structures, thalamus, andbasal ganglia (for reviews, see references 65 and84). Whether the striking increase in tone pre-ceding hand movement in our patients is relatedto activity from these more diffuse extrapyramidalpathways remains unknown, also whether theabnormality of tone results from or is an inherent


part of the movement disorder. It could even bethat alterations of tone are relevant to the partialsuppressibility of the mirror movements, and theinfluence of mood and relaxation on the fluctu-ation of discrete movements of the hands in dis-orders such as writers' cramp will be recalled.In addition, whilst the mode of action of bio-feedback remains unclear, the technique has forlong been used clinically to inhibit unwantedmotor activity;85 it is of interest that two of ourpatients very rapidly learnt to diminish theirmirrored movements transiently utsing bio-feedback-which perhaps argues in favour of effects ondiffuse possibly subcortical mechanisms.That a disturbance or anomaly of higher cor-

tical function could play a part in bimanual move-ments also requires consideration but appears un-likely,86 and we believe can be dismissed. In ourpatients there was no close association betweenmirror movements and intellectual ability or motorskill. Finally, we do not consider handedness to berelevant; two of our seven cases were sinistralsand the movements seen were no different in thesepatients.

We are grateful to Dr MFT Yealland, Dr KJZilkha, Professor WI McDonald and ProfessorCD Marsden for permission to publish details ofpatients under their care. We are also indebtedto the Department of Clinical Neurophysiologyfor the somatosensory evoked potential studies.

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Congenital mirror movements · JournalofNeurology,Neurosurgery,andPsychiatry, 1981. 44, 586-599...

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