Cauda Equina Syndrome in Ankylosing Spondylitis ...

1582 The Journal of Rheumatology 2019; 46:12; doi:10.3899/jrheum.181259

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Cauda Equina Syndrome in Ankylosing Spondylitis:Challenges in Diagnosis, Management, andPathogenesisChen Tang, Franklin G. Moser, John Reveille, Jane Bruckel, and Michael H. Weisman

ABSTRACT. Objective. Cauda equina syndrome (CES) is a rare neurologic complication of longstandingankylosing spondylitis (AS). It is unclear what causes CES, and no proven or effective therapy hasbeen reported to date. We have encountered 6 patients with longstanding AS diagnosed with CES.We set about to study their features, review the literature, and generate hypotheses regarding patho-physiology, as well as to speculate on the possibilities of early recognition and prevention.Methods. We obtained permission from 6 patients with longstanding AS and CES to access theirmedical records and imaging studies for research purposes related to this paper. We collected andreviewed each patient’s medical history, imaging studies, disease duration, past therapies especiallythose that relate to AS, laboratory data, as well as any treatment they received for CES and followupresults of each case to the present time. Results. The 6 cases of CES with AS have remarkable similarity to each other in that several decadesof the disease had passed before neurologic symptoms and later signs appeared. All cases have fusedspines and facet joints without spinal fractures, spinal stenosis, or disc herniation. Conclusion. CES is a rare yet debilitating neurologic complication of longstanding AS. The patho-physiology and treatments are far from clear. We postulate that chronic enthesitis of the vertebralcolumn initiates the process that results in dural stiffening and formation of ectasias, causingdownstream nerve root damage. (First Release August 15 2019; J Rheumatol 2019;46:1582–8;doi:10.3899/jrheum.181259)

Key Indexing Terms:ANKYLOSING SPONDYLITIS BACK PAIN NERVE COMPRESSION SYNDROMES

From the Departments of Rheumatology and Neuroradiology, Cedars-Sinai Medical Center, Los Angeles, California; University of TexasHealth Science Center at Houston, Houston, Texas; SpondylitisAssociation of America, Sherman Oaks, California, USA.C. Tang, MD, Departments of Rheumatology and Neuroradiology, Cedars-Sinai Medical Center; F.G. Moser, MBA, MD, Departments ofRheumatology and Neuroradiology, Cedars-Sinai Medical Center; J. Reveille, MD, University of Texas Health Science Center at Houston; J. Bruckel, BSN, RN, Spondylitis Association of America; M.H. Weisman,MD, Departments of Rheumatology and Neuroradiology, Cedars-SinaiMedical Center.Address correspondence to Dr. C. Tang, Cedars-Sinai Medical Center,Rheumatology, 8700 Beverly Blvd., Suite B-117, Los Angeles, California90048, USA. E-mail: [email protected] for publication March 19, 2019.

Ankylosing spondylitis (AS) is characterized radiologicallyand pathologically in its late stages by fusion of the sacroiliacjoints and ossification of tendons and ligaments at their sitesof attachment to bones1,2,3. Nonmusculoskeletal manifesta-tions include uveitis, pulmonary fibrosis, aortic valvulardisease, and amyloidosis2,4. Neurologic complications of ASare reported to occur in 2.1% of patients and include atlanto-axial subluxation with spinal cord compression or pathologicfractures of the rigid spine causing neurologic deficits2,4. Cauda equina syndrome (CES) is a rare neurologiccomplication of longstanding AS; its earliest descriptionsappear to have been done by Bowie, Glasgow, and Hauge in

19615,6. Dural ectasia with or without nerve root adhesion tothe enlarged dural sac is the typical finding seen on magneticresonance imaging (MRI) and the main diagnostic featureassociated with this condition7,8,9. It is unclear what causesCES, and no proven or effective therapy has been reportedto date. It is assumed that dural ectasia with subsequentfibrosis of the dura mater is the result of chronic inflammation, which at one point becomes unrecov-erable10,11,12,13,14. However, it is possible that unique featuresrelated to spinal and dural anatomy and the distribution ofmechanical forces in the thoraco-lumbar spine taking placeover time in patients with AS may have an as-yet-unrecog-nized contribution to the etiopathogenesis of CES. Challenges related to the management of CES are almostoverwhelming; case reports of patients treated with tumornecrosis factor inhibitors (TNFi), and lumbo-peritonealshunting (LPS), have shown some effect, while other reportshave revealed no improvement15,16,17,18,19,20. CES, a rare butnevertheless well-defined neurologic complication oflongstanding AS, has an extremely important effect onphysical function and patients’ quality of life. We haveencountered 6 patients diagnosed with CES, all of whomhave had longstanding AS. We set about to study theirfeatures in detail, review the literature, and generatehypotheses regarding why this event occurs, as well as

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speculate on the possibilities of early recognition andprevention.

MATERIALS AND METHODS We obtained permission from 6 patients with longstanding AS and CES toaccess their medical records and imaging studies for research purposesrelated to this case series and review. One of the 6 patients had died, and herhusband gave permission. All patients gave permission to discuss their caseswith them to fill gaps where necessary. The process by which the investi-gators achieved access to personal health information from these subjectswas approved by the Cedars-Sinai Institutional Review Board (IRB). NoIRB or ethics approval was required. We collected and reviewed each patient’s previous medical history,imaging studies, disease duration, past therapies (especially those that relateto AS), laboratory data, as well as any treatment they received for CES, andfollowup results of each case to the present time.

RESULTS Patient demographics and characteristics are shown in Table1 and Table 2. Patient 1 is a 70-year-old female with almost40 years of AS who reported a very slow progression (over14 yrs) of “pins and needles” sensations in the right foot.Symptoms progressed to involve the right leg along withincreasing numbness. Eight years after symptom onset, shestarted experiencing a change in her bowel habits with morefrequency and urgency, and then constipation. After 6 moreyears, she noticed slight weakness of the right quadriceps.She stopped playing competitive table tennis when the “pinsand needles” sensation intensified, and numbness began toinvolve the buttock and perineum, and urinary urgencydeveloped. She had been taking nonsteroidal antiinflam-matory drugs (NSAID) and etanercept for her AS almost theentire time she had experienced the above neurologicsymptoms. MRI of the lumbar spine showed diffuse bonyfusion, and L1-L2 dural ectasia involving the right posteriorelements with a posterolateral dural diverticulum. There wasassociated displacement of the distal conus, filum, and nervesof the upper cauda equina to the right, suggestive ofassociated tethering (Figure 1). She received 4 doses ofinfliximab (IFX) but stopped after shingles developed.Laminectomy with untethering was performed. Dural patch

placement was performed; however, the patch dehiscedweeks after the procedure. She did not experience relief inher symptoms with medical or surgical treatments. She nowhas chronic constipation and urinary retention that is beingtreated with medications. Physical activity, includingprolonged sitting, is difficult for her at the present time. Patient 2 is a 69-year-old male with a 20-year diagnosisof AS who reported 2 years of numbness and tingling inbilateral lower extremities that progressed to involve thesaddle region. Pain became dominant as well as numbness.Urinary and bowel incontinence began to develop, and helearned to self-catheterize for relief. He could ride his bicycleup to 50 miles on occasion prior to the diagnosis of CES. Heused only NSAID for the treatment of his AS. Inflammatorymarkers were always normal. MRI of the spine disclosedmultilevel remodeling and dehiscence of the posteriorelements; there were multiple L1-S1 thecal sac sacculationswith scalloping of the lamina, and disposition of the caudaequina into those sacculations. He continued to take NSAIDwithout improvement of his symptoms and now requires acane for ambulation. Patient 3 is a 69-year-old female (now dead) with over 30years of AS, who presented with 2 years of numbness andpain in the right buttock radiating to the right lower extremity,as well as numbness of the left foot. She had associatedweakness of the lower extremities and loss of sensation withurination and bowel movements. These symptoms caused herto use a cane and stop driving. Physical examination showedatrophy of the calf muscles, absent ankle jerk reflexes, andabnormal sensation testing. MRI revealed dural ectasia L2-L4with adhesive arachnoiditis (Figure 2). She received a short6-week course of adalimumab (ADA) without improvement.Laminectomy and epidural steroid injections did not help.Subsequently she was diagnosed with metastatic pancreaticcancer and died shortly thereafter. Patient 4 is a 65-year-old male with almost 40 years of ASwho presented with left foot drop associated with pain,numbness, weakness, and muscle atrophy over 4 years induration. His symptoms extended proximally and began to

1583Tang, et al: Cauda equina syndrome in AS

Table 1. Demographic summary of 6 patients with cauda equina syndrome (CES).

Patient Status Sex Age, HLA-B27 Extraspinal Family Smoker Physical Spinal TNFi before Treatment for AS yrs Disease Hx of SpA Activity Radiation Dx of CES before CES

1 Alive F 70 Yes No No No Competitive Yes Yes NSAID, etanercept table tennis2 Alive M 69 Yes No Yes No Swim, bike No No NSAID (20–50 mi)3 Dead F 69 Yes No No No Unknown Unknown No NSAID4 Alive M 65 Yes Iritis No Yes Unknown Unknown No NSAID5 Alive M 70 Yes Iritis, colitis, Reactive No Unknown Unknown No NSAID enthesitis arthritis6 Alive M 69 Unknown Iritis, colitis, No Yes Walk, bike, swim No No NSAID enthesitis, psoriasis

AS: ankylosing spondylitis; Dx: diagnosis; NSAID: nonsteroidal antiinflammatory drugs; TNFi: tumor necrosis factor inhibitor; SpA: spondyloarthropathy.




involve the right side as well. Physical examination disclosedsignificant muscle atrophy, weakness, and abnormal sensationfrom the feet to the buttock. MRI revealed left-sided L1-L3dural ectasia containing several descending nerve roots as well

as compressing the L5-S1 nerve roots. He had a bone spursurgical removal due to concern about nerve impingement butwithout benefit. He received ADA with unexpected worseningof symptoms, and this treatment was stopped.



Table 2. Summary of duration of disease at diagnosis, clinical features, treatments, and responses in 6 patients with cauda equina syndrome (CES).

Patient Age at Age at Age at Age at Duration of Presenting Sx Imaging Medical Response Surgery Response Mobility First Sx of Dx of First Sx Dx of Diagnosed of CES Abnormalitiesa Treatment for CES after CES AS, yrs AS, yrs of CES, CES, AS at Time for CES Dx yrs yrs of Diagnosed CES, yrs

1 21 29 51 65 36 Pins and needles of Yes Infliximab No Yes No Walks the R foot progressively (stopped for slowly, up to the perineum with shingles), duloxetine, cannot sit episodes of shock-like pain, gabapentin > 2 h numbness and weakness, urinary and bowel urgency 2 27 38 54 58 20 Numbness and tingling Yes NSAID No No No Cane in the feet and saddle, urinary and bowel incontinence 3 20 30 62 64 34 Saddle and R lower extremity Yes Pregabalin, No Yes No Cane pain, weakness, numbness, adalimumab tenesmus with bowel movement and urine4 20 24 59 63 39 L foot drop, weakness, Yes Adalimumab No Yes No Unknown atrophy, numbness and pain of the feet, then to legs5 Unknown 28 62 68 40 Numbness and pain of L foot, Yes Adalimumab Yes No NA Cane then leg and saddle; bowel, bladder, and sexual dysfunction6 18 25 47 52 27 Numbness, pain and Unknown NSAID No Yes Yes Cane weakness of the R foot with progression to the buttock and L side

a All patients had imaging findings of dural ectasia with displacement of the cauda equina, and ankylosis of the spine. There were no findings of spinal canalstenosis, foraminal narrowing, vertebral fracture, vertebral mass, disc herniation, or arachnoiditis in any of the imaging findings. Sx: symptoms; AS: ankylosingspondylitis; Dx: diagnosis; NSAID: nonsteroidal antiinflammatory drugs.

Figure 1. A. T2-weighted sagittal scan of the lumbar spine demonstrating the conus terminating at the L1 level.B. T1-weighted noncontrast sagittal scan of the lumbar spine showing a widely patent spinal canal.



Patient 5 is a 70-year-old male with 40 years of AS whopresented with 6 years of numbness and pain in the left footthat gradually ascended to involve the entire leg and groin.He also developed bladder, bowel, and sexual dysfunction.Because of the severity of his urinary issues, he had frequenturinary tract infections and nephrolithiasis. He now performsurinary self-catheterization. Physical examination revealsabnormal sensation in the left leg and absent ankle reflexes.MRI disclosed multilevel dural ectasias without tethering ofthe conus medullaris. He started ADA with subjectiveimprovement in pain. Strength and sensation returnedpartially to the perineum at the time of his last assessment. Patient 6 is a 69-year-old male with almost 30 years of ASwho presented with numbness of the right foot that extendedcaudally, followed by weakness of the calf, as well asinvolvement of the left lower extremity and saddle areas.Prior to the diagnosis of CES, he travelled extensively tomany national parks and participated in swimming and bikingexercise activities. MRI demonstrated extensive L2-L5 duralectasias. He underwent LPS with significant reduction inneuropathic pain; however, symptoms returned to previouslevels 2 to 3 years following surgery. He now uses a cane toambulate.

DISCUSSIONCES remains today a rare but devastating neurologic compli-cation of longstanding AS21. Damage to the nerve rootsappears to take place at the distal end of the spinal cord,resulting in sensory and/or motor deficits of the pelvis andlower limbs, including bladder and bowel dysfunction.Symptoms could develop rapidly, but most CES casesassociated with AS take years to develop, resulting in delayin diagnosis. There are no specific clinical or imaging criteria for thediagnosis of CES. The diagnosis is supported by symptoms

and radiographic findings. MRI is the preferred modality21.A list of red flag symptoms used to diagnose CES includeslow back pain, weakness, sensory loss or pain, saddleanesthesia, urinary or bowel dysfunction, sexual dysfunction,and reduced reflexes13. In patients with CES but without AS, the process is mostcommonly caused by lumbar disc herniation22 with a patho-genesis understood to be underlying spinal canal narrowingwith ligamentum flavum infolding22. Further injury to thenerves could be perpetuated by reactive inflammation fromany process, subsequently leading to nerve root compres-sion22,23,24. However, CES in patients with AS occurs withoutobvious spinal canal or foraminal narrowing, or disc herni-ation presenting the challenge to understand why it takesplace. The 6 cases of CES with AS described herein haveremarkable similarity to each other in that several decades ofthe disease had passed before neurologic symptoms and latersigns appeared. All cases have fused spines and facet jointswithout spinal fractures, spinal stenosis, or disc herniation.The diagnosis of AS was established in the patients’ early 30sbut symptoms of back pain likely occurred much earlier. Inaddition, none of the cases displayed other extraspinalmanifestations. Three of the 6 patients participated in veryactive recreational exercises. One case of CES developedwhile the patient was taking a TNFi; attempts at treatment ofestablished signs and symptoms of CES with anti-TNF agentsin the other cases did not reveal a pattern of success. The pathogenesis of CES in AS is unknown. Oneproposed theory is that the meninges expand in response tocerebrospinal fluid (CSF) pulse pressure, allowing increasedabsorption of the CSF and subsequent dampening of thetransmitted pressure variations12. Other suggested mecha-nisms include small-vessel angiitis of the vasa vasorum ofthe nerve roots, increased arterial pulsatile forces, or prior


Figure 2. A. T2-weighted axial scan at the L4 level in the lumbar spine demonstrating posterior dural ectasia. B. T2-weighted sagittalscan of the lumbar spine showing the posterior location of the abnormalities with the normal contour of the anterior spinal canal.




radiation treatments12. Koboyashi, et al25 studied caudaequina circulation of patients with neurogenic intermittentclaudication in lumbar spinal canal stenosis using dynamiccontrast-enhanced MRI; he and others found abnormalcontrast extravasation, delayed arterial uptake, and venouspooling of contrast that suggest disruption of the blood-brainbarrier, findings that often occur with chronic inflammationof any cause. It is possible, according to Koboyashi, thatedema from vascular compromise occurs secondary tochronic enthesitis in various tissues of the spinal canal in ASsubjects, which in turn causes irreversible damage to thespinal nerve roots over time25. Recent attempts from clinical and imaging studies andanimal model investigations to increase our understanding ofthe biomechanical basis for enthesitis do provide a unifyingconcept for enthesitis as a potential mechanism for devel-opment of CES in AS subjects3,26. The enthesis, a site of aligament, tendon, or joint capsule attachment to bone, maybe the pathway by which the loading forces of the spine canproduce inflammation, setting in motion the cascade ofevents leading to nerve damage in patients with CES. Basedon these newly evolving concepts of AS pathogenesis, wepropose that enthesitis in tissues of the spine is the incitingevent that leads to the multiple downstream sequelaeresulting in CES in patients with AS. Primary AS inflam-matory processes may extend to the dura mater from adjacententheses, causing inflammatory changes to the blood-nervebarrier and adhesion of the dura mater to the surroundingstructures, thereby resulting in reduction of compliance ofthe dural sac25,27. Stiffening of the dural sac would cause itto weaken over time, encouraging the development ofectasias28. The combination of mechanical distribution of theforces in the thoraco-lumbo-sacral spine, increased pressurein the lower vertebral column from a fused spine, associatededema, and reduced dural compliance, all of which couldcause the formation of dural ectasias29. Because moreligaments are found in the lateral-posterior portions of thespinal canal, it is possible that more enthesitis occurs in theseregions and weakening of these structures results in thecommon finding of posterior sacculations on imaging.Displacement, tethering, and vascular damage to the nerveroots over time could result in CES. For patients who have been taking biologic therapy withquiescent disease for years and then develop CES, one canargue that inflammation may not be the primary initiatingevent. However, it is likely that weakening of the dural sacwould have already occurred prior to initiation of biologictherapy, because in almost all cases CES develops in ASpatients with complete fusion of the spine. This suggests aprolonged latency period from clinically active disease todevelopment of CES following decades of apparent clinicalremission. A review of the anatomy of the spine segments involvedin AS does provide us with a critical view of where and when

CES may take place. There are 3 major ligaments in thespine: the anterior longitudinal ligament that runs along thefront of the vertebral bodies, the posterior longitudinalligament behind the vertebral bodies, and the ligamentumflavum that covers the dura mater and connects under thefacet joints13. These critical ligaments connect bones orcartilage elements together, providing stability to a jointduring rest and movement. The posterior longitudinal ligament is intimately adherentto the fibrocartilages and contiguous margins of the vertebraeand is connected to the most superficial layer of themeninges, the dura mater13. The dura has 2 layers: the super-ficial layer, which serves as the skull’s inner periosteum, anda deep meningeal layer13. When the dura covers the spinalcord, it is known as the dural or thecal sac. The dura alsobecomes the epineurium at the level of the dorsal rootganglion. The next layer of meninges is the arachnoid mater,which lines the dural sac13. The third and deepest layer of themeninges is the pia mater, which closely covers the brain,spinal cord, and the nerve roots, and eventually forms thefilum terminale, which arises from the conus medullaris andanchors the spinal cord to the coccyx. The cauda equinaconsists of nerve roots distal to the conus and containingafferent dorsal sensory fibers and efferent ventral motorfibers. These nerve roots enter the spinal cord through bothsides of the vertebral bodies, with every added cephaladnerve root displacing subsequent distal nerve roots poste-riorly, maintaining the orientation of motor fibers beinganteromedial, and sensory fibers posterolateral13. From an appreciation of the complex mechanical anatomyof the spine, we observe that the ligaments of the vertebralcolumn are closely associated with the meninges; therefore,enthesitis of the vertebral column would necessarily affectthe nerve roots. Weakening of the ligaments and underlyingmeninges could occur both from inflammation and erosionas well as from mechanical tension on the spinal connectivetissue from rigidity created by ankylosis. Zarzur28 observedthat the posterior lumbar dura mater was easily distensibleonly in the transverse direction. Therefore, fusion of the spinemay limit the ability of the dura to redistribute pressure; thisobservation, in part, may explain the specific mechanicalcontributions to the formation of posterior dural sacculations.We could not examine whether ossification or calcificationof the posterior longitudinal ligaments occurred in our patientcohort because of insufficient computed tomography imagingdata. The work of Tan, et al30,31,32 suggests that syndesmo-phytes (SM) are nonrandomly distributed around the discmargins, and they occurred most often at the posterolateralrim. We would expect random distribution of SM if they wereformed solely in response to inflammation. Further, orthope-dists and biomechanical engineers cite this area as the middlecolumn of the spine where mechanical stress is concentratedat the base of the pedicles. Therefore, these observations





suggest that mechanical forces in this area of the spine maybe important for SM’s initiation as well as in spinal enthesitis. There has been no demonstrated effective medical orsurgical treatment for CES once it occurs in AS20. Ahn, etal20 performed a metaanalysis for treatment effects of CESin AS and found that steroids had not been effective. WhileNSAID appeared to improve symptoms, they did not alterneurologic deficits20. Others reported improvement aftertreatment with IFX, but this is not consistent across reports17.Surgical intervention such as LPS, untethering, andlaminectomy also have achieved inconsistent results15,16.Some experts have suggested early medical treatment iscrucial for making as full a recovery as possible for typicalCES, especially in those who have evidence of active inflam-mation33. Unfortunately, early diagnosis is difficult, and treat-ments succeed inconsistently. The degree of recovery islimited even in those who have a partial response. This information raises the question of when CES shouldbe suspected in patients with AS. The following questionsneed to be addressed if we are going to understand how todiagnose and manage this condition. How and when do wescreen, predict progression, and differentiate CES from othercauses of pain and neuropathy? Is it too late to intervenewhen patients display the initial symptoms of neuropathy —when chronic inflammation presumably has already takenplace? Are physical mechanical forces on the spine a majorcause of CES in AS? Future attempts to identify at-riskpatients early may help us understand more about CES patho-genesis and treatment options. CES is a rare yet debilitating neurologic complication oflongstanding AS and the pathophysiology and treatments arefar from clear. Herein we reported 6 patients with CES andAS, and reviewed current understanding of the pathogenesisof CES in AS. We postulate that chronic enthesitis of thevertebral column initiates the process that results in duralstiffening and formation of ectasias, causing downstreamnerve root damage. Mechanical force transduction in thespine may play a pivotal etiologic role.

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