Preliminary Findings: Alternative Medicine

CHRONIC SUBMAXIMAL MAGNETIC STIMULATION IN PERIPHERAL NEUROPATHY: IS THERE A BENEFICIAL THERAPEUTIC RELATIONSHIP?

Abstract
Dysesthetic pain in the extremities of diabetics and other patients with neuropathies remains a refactory problem. Conventional treatment is largely symptomatic and often ineffective with frequent adverse effects. Potential neuroprotective effects of waering magnetic foot pads have been claimed anecdotally yet never scientifically assessed. In a pilot study, eight diabetic patients (Stage II and III) and six subjects with peripheral neuropathies (PN) from other etiologies wore magnetic foot pad insoles generating 475 gauss for 24-hour periods up to four months. Electrophysiological data by either nerve conduction velocity (NCV) and/or somotosensory evoked potentials (SSEP) were obtained at baseline and serially. Neuropathic pain scores, using a visual analog scale (VAS) were tabulated daily. No sham magnetic controls were used. Six/eight diabetic subjects experienced reduction or reversal of symptoms (75%), whereas in the the nondiabetic PN group only 50% improved. Burning feet dysesthesiae reversed in all four diabetic and one non-diabetic subject. Overall, the entire cohort nine/fourteen (64%) experienced a clinical benefit. VAS scores were considered significant only in the diabetic PN group. There was no electrophysiological change in A-fiber conductions, cortical, or root latencies. Submaximal, constant magnetic stimulation appears to influence small C-fibers selectively, whereas there were no clinical or electrophysiological changes in A-fiber function. Placebo effect could not be totally eliminated or evaluated in this pilot study. These results suggest that wearing magnetic foot pads may be a modifiable factor in intractable peripheral neuropathy. These data suggest that a double-blind placebo-controlled study is warranted.

Descriptors
diabetic neuropathy, dysesthesiae, peripheral neuropathy, magnetic biostimulation, magnetic foot pads

AJPM 1998;8:12-16. Received 5-23-97; Accepted: 9-5-97

INTRODUCTION

Diabetic peripheral neuropathy (DPN) is frequently an incapcitating disorder associated with high morbidity often running a progressive course (1,2). Typically, it begins insidiously producing symmetrical sensory complaints of numbness, tingling, and burning dysesthesiae. This is essentially a small C-fiber neuropathy (unmyelinated and small myelinated) with pathological distal axonal degeneration and secondary demyelination (3,4). Conventional treatment for painful DPN is largely symptomatic yet often ineffective and associated with unacceptable side effects (5). In view of the vulnerability of the peripheral nervous system in diabetes, alternative therapies directed at slowing or halting the process are deemed prudent.

Anecdotal reports suggest a public enthusiasm for magnetic devices as an alternative treatment for painful feet (6). It has been reported that there were $100 million in sales in the US and Canada in 1995 with estimated $1.2 billion in world-wide sales.

It has long been recognized that a variety of biological effects have been attributed to exposure to electromagnetic fields. Supermaximal magnetic stimulation is known to influence motor and sensory nerve functions, modifying the transport of ions across cell membranes and inducing evoked potentials (7-9). It is hypothesized that constant submaximal stimulation can preferentially activate sensory neurons and alter symptomatology by modifying membrane potentials, thereby producing a potential neuroprotective effect (10,11).

METHODOLOGY

From January 1995 through December 1996, 14 patients (ten males, four females), aged 44-85 years (mean age 62 years) with diagnosis of peripheral neuropathy were investigated. In this group were patients with chronic DPN (DPN, Stage II and III) (12) who were unresponsive to conventional therapies. Four also complained of burning feet, and two displayed bilateral foot drop. Three subercts were impotent, and one also displayed a mononeuritis multiplex.

The main clinical criteria adopted for entry into the study was evidence of progressive and disabling peripheral neuropathy. The duration of disease of diabetes at the time of electrophysiological testing ranged from two to sixteen years. Six additional participants in this study were individuals with clinical and/or electrophysiological evidence of peripheral neuropathy (PN) secondary to alcohol, hexane, vasculitis, chemotherapy (2 patients), or Guillain-Barre-Strohl; and three patients also had malignancy (prostate, colon, breast). These patients comprised the nondiabetic PN (N-DPN) cohort. The investigation was approved by the Human Research Committee of Phelps Memorial Hospital. All patients received and gave informed consent.

Standardized non-invasive electrophysiological data on nerve functions were obtained using either nerve conduction velocity (NCV) and/or somatosensory evoked potentials (SSEP) at baseline and compared serially at three to four month intervals. Nerve conduction and electromyography studies were performed on a TECA Model M using standard techniques. Motor conduction of peroneal and tibial nerves as well as sensory conduction velocities, amplitude, latencies, and F-wave latencies. Needle examination was performed only at baseline.

Measures of dermatomal somatosensory potentials (SSEP) are a reproducible method of determining the functional status of the large diameter afferent A-fibers. Electrophysiologic parameters were analyzed by comparing latencies of the peroneal and tibial nerves, P37 cortical potentials, and cutaneous dermatomal nerve root latencies (L4, L5, S1) at baseline and at three to four months.

Patients were instructed to quantify their pain twice a day, at the same times, for up to four months using a visual analog scale (VAS) (anchored as 0-4; 0=none; 1=normal; 2=moderate; 3=severe; 4=worst)(13). Since neuropathic pain can fluctuate, the 30-day composite scores are assessed to obtain a specific numerical mean pain level pre- and post-treatment. The primary outcome was reduction in their self-rated pain score; secondary outcome measures were changes in the neurological examination and electrophysiological studies (NCV/SSEP).

Magnetic foot pad insole devices (Magsteps) are permanent neodymium magnets with a 475 gauss steep field gradient. There is a geometric multi-polar triangular arrangement (north/south) which produces a static submaximal magnetic field. Penetration of this field is 4 cm (1.75"). Since magnetic field strength drops-off significantly with distance, subjects were instructed to wear the magnets in their shoes during the day and then remove them and sleep with them inserted into their socks. Thus, 24 hours of direct, continual contact was established for a duration of up to four months. These devices are commercially available; no sham devices were used as controls.

STATISTICS

Results are reported as the mean ąSD. Statistical analysis was done on group mean values using the student t-tests. A p-value of less than 0.05 was considered to be significant.

RESULTS

All patients tolerated the waering of magnetic foot pads continually without complications. At completion of the study, six of eight diabetic patients (75%) experienced a pronounced improvement in symptoms, three totally without complaints. Burning dysesthesiae reversed in all four patients who had previously had these complaints. The earliest improvement was noted in 14 days, and this individual only wore the magnets for 15 hours per day. Three subjects had a sensation of foot warmness. One subject consumed a high carbohydrate meal and noted a return of symptoms temporarily. Interestingly, five patients noted that withdrawl of the magnets led to a return of the symptoms. Most benefit in five/six patients occurred between the second and third month. There were two failures in this group: one male patient had a 16-year history of diabetes with mononeuritis (foot drop), femoral neuropathy, peripheral neuropathy, and impotence, and the other male patient had an 11-year history of diabetes with impotence and glucose = 434 mg/dl and triglycerides = 1800 mg/dl and cholesterol = 346 mg/dl. Severe axonal and demyelinating changes were noted on EMG/SSEP. The VAS scores were statistically significant (p < 0.05) in four subjects: one subject improved yet the score did not reflect this. Two subjects did not submit scores.

In the second group of N-DPN, three patients (50%) achieved clinical improvement with pins/needles/tingling or burning symptoms (etiology of malignancy, vasculitit, GBS). However, the VAS score improvement in these subjects was not considered statistically significant. Two patients did not submit VAS scores. The symptom of burning feet was present in three individuals with only one improving (33%) (etiology of breast cancer with chemotherapy). The three unresponsive subjects in this group demonstrated severe axonal and demyelinating changes on EMG (2 patients) and one had combination of malignancy and hexane toxicity.

If one looks at both groups (Table I), a total of seven subjects experienced burning dysesthesias and five/seven responded (71%). Paresthesias of numbness and tingling improved in nine/fourteen (64%). Clinically, there were no significant neurological changes in DTR/sensation or motor strength. There were no significant electrophysiologic changes identified in serial conduction velocities, cortical potentials, or dermatomal root latencies in eleven/fourteen patients.

Table II. VAS scores.