Static Magnetic Fields for the Treatment of Pain

a

Epilepsy & Behavior 2, S74–S80 (2001)

doi:10.1006/ebeh.2001.0211, available online at http://www.idealibrary.com on

Static Magnetic Fields for the Treatment of Pain

Michael McLean, M.D., Ph.D.,1 Stefan Engstrom, Ph.D.,nd Robert Holcomb, M.D., Ph.D.

Department of Neurology, Vanderbilt University Medical Center,Nashville, Tennessee 37212

Received May 11, 2001; accepted with publication May 14, 2001

Unlabeled/investigational or unapproved use of products will be presented in this article.

Therapeutic magnets constructed with permanent magnets that generate static magnetic fields havegained popularity in recent years. Federal authorities in the United States do not currently regulatesales. The marketed devices are not FDA approved. Nonetheless, there is a body of published datathat supports potential therapeutic utility of static magnetic field–generating devices. This body ofknowledge is critically reviewed here. Characterization of effective field metrics and mechanisms ofinteraction with biological substrates are incomplete. The design of magnetic placebos for maskingin long-duration studies is essential. Current evidence suggests that there is merit in continuing todevelop and test therapeutic magnetic devices. © 2001 Academic Press

Key Words: therapeutic magnets; magnetotherapy; pain management; Magna Bloc; Nikken; Bioflex;low back pain; magnetic placebos; medication-resistant neuropathic pain.

Application of static magnetic field-generating de-vices to the skin over painful areas of the body withtape or elastic wraps has become a popular method forthe treatment of day-to-day pains. Many types of mag-netic devices are available on the shelves of pharma-cies, groceries, and department stores. Worldwidesales have been reported to exceed $5 billion (1).Nonetheless, the fundamental basis for therapeuticuse of magnetic fields has not been established to theextent necessary for acceptance by the conventionalmedical community. Also, though such devices ap-pear to have no significant risk and their sale is notregulated at the present time, no static magnetic field-generating device has been approved by the FDA formarketing to treat a specific medical condition.

A number of criteria, including the following, mustbe met to achieve acceptability among medical prac-

Robert R. Holcomb is the inventor of the Magna Bloc. He is amajor shareholder, and Michael J. McLean is a minor shareholder, incompanies involved in commercialization of the device. This par-ticipation could result in monetary gain for them personally.

1 To whom correspondence should be addressed at Departmentof Neurology, Vanderbilt University Medical Center, 2100 PierceAvenue, 351 MCS, Nashville, TN 37212. Fax: (615) 936-0223. E-mail:[email protected].

S74

titioners and regulatory agencies: (a) The magneticfield produced by each device must be characterizedand its depth of penetration into tissue determined. (b)Biological effects of magnetic fields to be used in clin-ical trials must be demonstrated in relevant animaland cell models. (c) Effects of specific magnetic field-generating devices must be demonstrated in humansubjects in pilot studies so that larger controlled stud-ies can be designed to test positive findings. This sameprinciple drives development of pharmaceuticals. Forexample, an antiepileptic drug is shown to have effi-cacy in animal models and in limited phase II testing(equivalent to pilot studies, including dose-ranging)before pivotal placebo-controlled trials are undertakenin phase III. (d) Large controlled studies must demon-strate superiority to placebos and, preferably, also othermagnetic devices. To examine the current status of mag-netotherapy for pain, we summarize our own efforts thathave used these criteria and review recently publishedresults of controlled trials. All of the devices describedhere are commercially available, and the research re-viewed here was supported by private funds.

We have examined effects of a static magnetic fieldwith marked spatial variation produced by a squarearray of four cylindrical permanent magnets (NdFeB)of alternating polarity (Magna Bloc; Figs. 1A, 1B).

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All rights of reproduction in any form reserved.

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Positioning cultured neurons above the device along aperpendicular line drawn from the middle of the in-terpole line to the center (maximally effective region,MER) resulted in significant effects on the neurons.Lesser effects have been obtained by positioning thecells near the center or over the poles. Gradients (dB/dx, change of field strength with distance) in the mag-netic field are important in determining biological ef-ficacy (2). Modeling has shown that the MER coin-cided with regions in which the gradient (dB/dx) is

redominantly perpendicular to the local field vectorFig. 1C).

Placing cultured neurons at effective distances overhe MER resulted in reversible, time-dependent block-de of electrically stimulated action potentials of cul-ured mouse dorsal root ganglion cells without alter-ng resting membrane potential (3, 4) (Fig. 2A). Re-

FIG. 1. (A) Field map produced by canning with a gaussmeter oriurface of the alternating quadrupolar array depicted in the cartoon.agnitude. This three-dimensional plot is important in showing the

wo poles) and the steep decline of the field strength from the poleeld (dB/dx) are perpendicular to the field strength (B). Abscissa u

ponses of neurons to the pain-producing substanceapsaicin also were blocked reversibly over the MER5) (Fig. 2B). Calcium–calmodulin-mediated myosinhosphorylation is enhanced by placing the reactionhamber over the MER (Engstrom et al., submitted).ositioning of cultured neurons over the MER alsorotected against kainate-induced swelling and celleath (6). This neuroprotective effect may result from

nteraction of the magnetic field with multiple steps inpathway leading to generation of inositol triphos-

hate and the release of intracellular calcium (6).hese different lines of evidence suggest that the MERas unique properties that enhance or diminish bio-

ogical activities. Other regions of the field had less oro effect on these different preparations (Fig. 2).The mechanism(s) of interaction of the field with

ell components is not known. Time dependence sug-

n z plane shows the contour of the field measured 3 mm above theurtesy of Dr. John Wikswo. (B) Calculated total fields showing fieldfield between the poles (note slight decline in the saddle between

enter. (C) Calculated regions in which gradient components of them throughout; ordinate units: mT in (A) and (B), T/m in (C).

ented iScan co

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S76 McLean, Engstrom, and Holcomb

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gests slow changes in conformation of ion channels orenzymes, e.g., resulting in phosphorylation/dephos-phorylation of sodium channels. A different staticmagnetic field (123 mT), with no detectable gradient,decreased activation of calcium channels of clonedpituitary cells (7) and reduced acetylcholine release ata neuromuscular junction in a calcium-dependentmanner (8). In summary, these findings suggest aplausible mechanism or mechanisms by which mag-netic fields change conformation of transmembraneand soluble proteins to produce significant biologicaleffects. Also, modeling and multifactorial analysis ofthe field produced by the alternating quadrupolar ar-ray also suggest a possible metric by which the inter-action with biological substrates occurs.

In a double-blind, placebo-controlled, randomizedcrossover pilot study of 54 patients with mechanicallow back and knee pain, reduction of pain duringtreatment with devices consisting of the alternatingquadrupolar array (referring to the poles facing theskin; Magna Bloc) was superior to that during treat-

FIG. 2. Effects of exposure to the MER of field produced by the ahe array. (A) Reversible blockade of electrically stimulated action

onolayer dissociated cell culture. Each panel shows multiple supeleftmost panel), the array was positioned beneath the neuron unde

agnetic field, AP latency fluctuated and maximal rate of rise declinailed to elicit AP, despite doubling of stimulus intensity that was of latency and increasing rate of rise by 5 minutes and recovery to c

maximal rate of rise (indirect measure of inward sodium current gvoltage. Bottom: intracellularly applied depolarizing current pulses.(calcium-dependent) applied intermittently by pressure ejection fo(leftmost panel), magnetic field exposure over the MER resulted inrecovery occurred 5 minutes (fourth panel) after and full recoveryright. Times at bottom apply to respective columns of panels in ro

Copyright © 2001 by Academic Pressll rights of reproduction in any form reserved.

ment with nonmagnetic placebos (P , 0.03) (9). Athick foam pad covered the devices to maintain mask-ing. The study entailed two 24-hour periods of obser-vation, 1 week apart. The order of treatments wasrandomized. Knee pain responded better than backpain. No significant adverse events occurred.

A larger study involved patients with mechanicallow back pain only (10). The study design was similarto the pilot study. In the per protocol analysis, treat-ment with the Magna Bloc devices produced signifi-cantly greater pain relief than placebo by three instru-ments of measure: (a) at 3 hours by the visual analogscale (11, 12); (b) at 3 and 24 hours by the verbalresponse scale (P 5 0.02 for both times) (13); and (c) byreduction of average pain over 24 hours based onself-reported patient diaries (P , 0.01). The internalconsistency of the findings suggests that extendedwearing of devices incorporating the alternating qua-drupolar array may reduce chronic mechanical lowback pain of moderate intensity. Characteristics ofthese two studies are listed in Table 1. Larger patient

ing quadrupolar array with the neuron 5 mm above the surface oftial (AP) firing by adult mouse dorsal root ganglion neurons ined traces to assess fluctuations in latency. After control recordings

y (Magnet Array, center panels). After 1 minute of exposure to thee stimuli failed to elicit AP. After 5 minutes, 10 consecutive stimuli

e constant throughout. Recovery of AP occurred with abbreviationstatus by 10 minutes. Top: dV/dt, maximal downward deflection 5ng AP upstroke). Middle: intracellularly recorded transmembraneations to right. (B) Responses of another neuron to 1025 M capsaicinonds (bars beneath traces). After control responses were obtainedependent reduction (second panel) and block (third panel). Partialinutes after removal of the magnetic array. Calibrations shown at

and (B).

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populations are needed to minimize the impact ofvariability of pain, and longer studies are needed toassess duration of pain relief.

We contrast these findings with results of a pilotstudy of a different magnetic device (Nikken) for thetreatment of chronic low back pain (14) (see Table 1).This study involved 20 individuals with low back painassociated with a variety of pathologies. Field strengthwas roughly 30 mT at the device surface, but there wasno further characterization of the field or its depth ofpenetration and no reference to basic studies. Demag-netized devices served as placebos. This was a double-blind, placebo-controlled, crossover study in whichsubjects wore one device 6 hours per day on Monday,Wednesday, and Friday of one week and then theother device in similar fashion, with a 1-week washoutperiod between the two treatments. There was nostatistical difference between pain intensities reportedby the visual analog scale during the two treatments.The rationale for treatment with the devices everyother day is not clear, and this is the only studyreviewed here in which wearing of the magnetic de-vice was intermittent. The authors state that one pos-sible reason for failure to see a difference in the treat-ments might be the limited penetrability of the mag-netic field. If the field did not envelop the pain-generating structures, this pilot study would notconstitute a test of efficacy of the magnetic field. With-out characterization of the field produced by thesedevices, and given the heterogenous study popula-tion, the chance of a significant outcome from thisstudy design was no better than chance.

Magnetic insoles (Nikken Magsteps) were em-ployed to test efficacy against medication-resistantneuropathic pain in 10 patients with diabetes and 9patients with other neuropathic disorders (1) (Table 1).In the first month, patients were randomized to treat-ment of one foot with a magnetic insole and the otherwith a nonmagnetic placebo insole. In the secondmonth, the treatment devices were switched. In thefinal 2 months, both feet were treated with magneticinsoles. Patients were instructed to rate their paintwice daily using a 5-point scale. Pre- and posttreat-ment composite scores (30-day mean pain scores)were compared. Burning was assessed separatelyfrom numbness and tingling. Four individuals in thediabetic cohort withdrew: two because of surgery forresidual foot infections, one because of inability totolerate the insoles on painful feet, and one because ofadministrative issues. During the first 2 treatmentmonths in which one foot or the other was treatedwith a placebo, there was no significant reduction of


the mean composite pain scores. Between the secondand third months, pain scores of the diabetic groupdeclined about 80%. Numbness and tingling also de-clined between months 2 and 3 in the diabetic groupbut not in the nondiabetic group. Nine of ten diabeticswere said to have benefited (not defined) comparedwith three of nine among the nondiabetic neuropathicgroup. Pain returned after removal of the devices.Carryover effects could not be eliminated becausethere was no washout period between treatments. Useof placebos in only the first half of the study makes theanalysis questionable. The fields and biological effec-tiveness of the active devices were not characterized inany detail. Pain intensities were mild (,1 on a scale of0 to 5) and improvement could be difficult to discrim-inate in this range. In a long study such as this, it isdoubtful that masking could be protected for 4 monthswith nonmagnetic placebos. The study was designedto evaluate the placebo, but patients could not distin-guish between placebo and active treatment duringthe first 2 months. For these reasons, the report of apositive outcome is difficult to interpret. A largerstudy is in progress.

Magnetic devices of a different size (5 3 8-cmNikken pads), but presumably the same magneticfield characteristics as the two devices describedabove, were also used to determine effectiveness indecreasing postexercise pain (15). A single-blind pla-cebo-controlled design was used. A protocol of con-centric–eccentric exercise of the biceps brachiae wasused to induce muscle soreness and microinjury. Aftercompletion of the exercise, patients were treated witheither placebo or active magnetic device for 72 hourswith assessments of pain, upper arm girth, range ofmotion, and static force production at 24-hour inter-vals. The 5 3 8-cm device covered only the midbodyof the biceps. No rationale is given for this procedure,and there is no indication that pilot studies involvingdifferent arrangements or the use of multiple mag-netic pads were tried. The visual analog scale wasused to assess pain. There was no statistically signifi-cant difference between treatments for any of the pa-rameters measured. Without characterization of themagnetic field produced by the device, the depth ofpenetration could not be assessed. In the absence oflaboratory studies, there are no parameters for thresh-olds of field strength or field gradient that could beanticipated to bring about a therapeutically beneficialresult. No mention was made about intactness of themasking. Partial coverage of the biceps by the mag-netic device could be insufficient to produce detect-able therapeutic benefit. Under the conditions of the


experiment, no significant benefit was achieved. Thisdoes not prove that magnetic fields of similar or dif-ferent design are without potential for treating mus-culoskeletal injuries and pain under optimal studyconditions.

Lastly, magnets of a different design (Bioflex 30 or50 mT at the surface of the devices) were tested forefficacy against trigger point pain in 55 patients withpostpolio syndrome (16). The study was double-blind,randomized, placebo-controlled, and involved paral-lel groups. The primary instrument of measure wasthe McGill pain questionnaire. After baseline mea-sures, patients were randomized to treatment witheither active or nonmagnetic placebo devices. The de-vices were placed over trigger points. After 45 minutesof treatment, the devices were removed, and triggerpoints were again palpated to assess pain. Pain im-proved in 22 of 29 subjects treated with active devicesand in 4 of 21 treated with the nonmagnetic placebos.Reduction of mean pain intensity during treatmentwith the active magnetic devices was statisticallygreater than that during treatment with the nonmag-netic placebos (P , 0.0001). The duration of pain reliefafter treatment of the active devices was not assessed.The authors concluded that magnetic fields of 30 to 50mT applied over painful trigger points resulted insignificant and prompt relief of pain in patients withpostpolio syndrome. This study uses standardized as-sessment tools in a well-controlled environment inwhich masking appears to have been protected. Thepressure applied to trigger points to elicit pain was notquantified or controlled, although investigators triedto be consistent. The brief period of treatment limitsconclusions to the rate of onset of benefit and is notsufficient to guarantee protracted benefit. No adverseevents were encountered. This statistically significantresult in a pilot study encourages further investigationwith skin-applied static magnetic field-generating de-vices.

CONCLUSIONS

Despite problems of study design that limit inter-pretability of the studies described above, this critiquesuggests that there is a growing body of data from thelaboratory and from controlled trials that, even if ru-dimentary, justifies further research with therapeuticstatic magnetic field-generating devices. As indicatedabove, both efficacy and inefficacy of poorly charac-terized devices are uninformative. Better characteriza-tion of devices and the development of appropriate

magnetic placebos are required for future studies.Some studies lack the precedent of reducing pain inpilot studies. This means, in effect, that the investiga-tors cannot know whether they are testing a demon-strable effect. We suggest that the plan of investigationoutlined at the beginning of this discussion be fol-lowed in an effort to adduce compelling mechanisticand clinical trial data. This is necessary to compete forpublic/federal funding and to achieve federal regula-tory approval.

At the heart of understanding apparent discrepan-cies lies the problem of learning how to study thesedevices. Therapeutic magnets are applied locally.They have the advantage of being free of adverseeffects of systemically administered analgesic medica-tions, such as gastritis. But the devices must be posi-tioned critically to have any chance of providing ben-efit. As a result of distribution throughout the body,pharmaceuticals may affect more than one targetalong the pain-processing pathway. To do so withmagnetic devices requires positioning multiple de-vices over different points along the processing path-way. The magnetic fields may only be effective in thelimited tissue volumes they envelop, a feature thatshould minimize adverse events. Every aspect ofstudy design must be optimized for the specific devicebeing tested. Finding appropriate conditions to testspecific fields is the first step toward the design ofinformative studies.

REFERENCES

1. Weintraub M. Magnetic biostimulation in painful diabetic pe-ripheral neuropathy: a novel intervention—a randomized,double-placebo crossover study. Am J Pain Manage 1999;9:8–17.

2. Cavopol AV, Wamil AW, Holcomb RR, McLean MJ. Measure-ment and analysis of static magnetic fields that block actionpotentials in cultured neurons. Bioelectromagnetics 1995;16:197–206.

3. McLean MJ, Holcomb RR, Wamil AW, Pickett JD. Effects ofsteady magnetic fields on action potentials of sensory neuronsin vitro. Environ Med 1991;8:36–44.

4. McLean MJ, Holcomb RR, Wamil AW, Pickett JD, Cavopol AV.Blockade of sensory neuron action potentials by a static magneticfield in the 10 mT range. Bioelectromagnetics 1995;16:20–32.

5. Wamil A, McLean M, Holcomb R. Blockade of capsaicin re-sponses of cultured sensory neurons by a static magnetic field.Submitted for publication.

6. McLean MJ, Holcomb RR, Engstrom S, Sanderson L, Mc-Donald PW, Thomas RM. A static magnetic field reduces neu-ronal swelling and death produced by kainic acid. Paper pre-sented at the Proceedings of the Millennium InternationalWorkshop on Biological Effects of Electromagnetic Fields; 2000Oct 17–20, Heraklion, Crete, Greece, pp 502–8.


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Static Magnetic Fields for the Treatment of Pain

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