Epilepsy & Behavior. 2001;2,S74-S80
Static Magnetic Fields for the Treatment of Pain
McLean MJ, Engstrom S, Holcomb RR
INTRODUCTION
Therapeutic magnets constructed with permanent magnets that generate static magnetic fields have gained popularity in recent years. Federal authorities in the United States do not currently regulate sales. The marketed devices are not FDA approved. Nonetheless, there is a body of published data that supports potential therapeutic utility of static magnetic field–generating devices. This body of knowledge is critically reviewed here.
Characterization of effective field metrics and mechanisms of interaction with biological substrates are incomplete. The design of magnetic placebos for masking in long-duration studies is essential. Current evidence suggests that there is merit in continuing to develop and test therapeutic magnetic devices.
Application of static magnetic field-generating devices to the skin over painful areas of the body with tape or elastic wraps has become a popular method for the treatment of day-to-day pains. Many types of magnetic devices are available on the shelves of pharmacies, groceries, and department stores. Worldwide sales have been reported to exceed $5 billion.
Nonetheless, the fundamental basis for therapeutic use of magnetic fields has not been established to the extent necessary for acceptance by the conventional medical community. Also, though such devices appear to have no significant risk and their sale is not regulated at the present time, no static magnetic fieldgenerating device has been approved by the FDA for marketing to treat a specific medical condition.
A number of criteria, including the following, must be met to achieve acceptability among medical practitioners and regulatory agencies: (a) The magnetic field produced by each device must be characterized and its depth of penetration into tissue determined. (b) Biological effects of magnetic fields to be used in clinical trials must be demonstrated in relevant animal and cell models. (c) Effects of specific magnetic fieldgenerating devices must be demonstrated in human subjects in pilot studies so that larger controlled studies can be designed to test positive findings.
This same principle drives development of pharmaceuticals. For example, an antiepileptic drug is shown to have efficacy in animal models and in limited phase II testing (equivalent to pilot studies, including dose-ranging) before pivotal placebo-controlled trials are undertaken in phase III. (d) Large controlled studies must demonstrate superiority to placebos and, preferably, also other magnetic devices.
To examine the current status of magnetotherapy for pain, we summarize our own efforts that have used these criteria and review recently published results of controlled trials. All of the devices described here are commercially available, and the research reviewed here was supported by private funds. We have examined effects of a static magnetic field with marked spatial variation produced by a square array of four cylindrical permanent magnets (NdFeB) of alternating polarity.
Positioning cultured neurons above the device along a perpendicular line drawn from the middle of the interpole line to the center (maximally effective region, MER) resulted in significant effects on the neurons. Lesser effects have been obtained by positioning the cells near the center or over the poles. Gradients (dB/ dx, change of field strength with distance) in the magnetic field are important in determining biological efficacy .
Modeling has shown that the MER coincided with regions in which the gradient (dB/dx) is predominantly perpendicular to the local field vector. Placing cultured neurons at effective distances over the MER resulted in reversible, time-dependent blockade of electrically stimulated action potentials of cultured mouse dorsal root ganglion cells without altering resting membrane potential. Responses of neurons to the pain-producing substance capsaicin also were blocked reversibly over the MER.
Calcium–calmodulin-mediated myosin phosphorylation is enhanced by placing the reaction chamber over the MER (Engström et al., submitted). Positioning of cultured neurons over the MER also protected against kainate-induced swelling and cell death. This neuroprotective effect may result from interaction of the magnetic field with multiple steps in a pathway leading to generation of inositol triphosphate and the release of intracellular calcium. These different lines of evidence suggest that the MER has unique properties that enhance or diminish biological activities.
Other regions of the field had less or no effect on these different preparations. The mechanism(s) of interaction of the field with cell components is not known.