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American Pain Society
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R. Norman Harden, MD, Department Editor
Marko Markov, PhD
Department Editor’s Note: In the 1950s and 1960s the established scientific community predicted that magnetic fields could never be used to image the body, and ridiculed the efforts of those involved in that research. Now we have magnetic resonance imaging. The body is bioelectric and therefore biomagnetic. It is logical to assume that electromagnetic energy should impact the function of organisms, perhaps therapeutically. There are randomized controlled trials available, and in progress, that are sorting out the true value of magnetic therapy in human disease and pain.
Despite the significant success of western medicine in the second half of the 20th century, there are a number of conditions associated with acute or chronic pain for which successful treatments were not established. While acute pain is related mainly to traumatic injuries or swelling/inflammation and can be easily controlled, chronic pain represents a serious problem for society. The National Institutes of Health estimates that more than 48 million Americans suffer chronic pain, resulting in a $65 billion annual loss of productivity and more than $100 billion in pain care costs. Today, western medicine is based mainly on the achievements of chemistry that have been used and expanded by the pharmaceutical industry. Unfortunately, almost all pharmaceuticals affect not only the target tissues, but also the entire organism and, in many cases, initiate adverse effects. In contrast, physical medicine in general—and magnetobiology in particular—provides non-invasive, safe, and easily applied methods to directly treat the site of injury and the source of pain and inflammation.
Recent advances in biomagnetic technology make magnetic fields (MFs) and electromagnetic fields (EMFs) useful modalities for treatment of various pathologies and diseases. It has been shown that EMFs provide a practical, exogenous method for inducing cell and tissue modifications, correcting selected pathological states. A number of clinical studies, in vivo animal experiments and in vitro cellular and membrane research, suggest that MF and EMF stimulation can significantly reduce pain and accelerate the healing process. However, EMFs are still not widely used in clinical medicine.
Interest in MF therapy in the United States was stimulated in the last decade by the large commercial marketing of permanent magnets (triggering the interest of the general public) and by the activity of the Office of Alternative and Complementary Medicine. Some of the most enthusiastic users of MF therapy are medical practitioners who already have experience in using acupuncture. Another driving force is the fact that more than 1 million patients have been treated with MF therapy worldwide, with application to practically all areas of fracture management. The patients already treated with EMFs have exhibited a success rate of approximately 80%, with virtually no reported complications after more than 2 decades of use (Bassett, 1989, 1994). While the success rate for EMF therapies is comparable to that produced surgically for delayed and nonunion fractures, the cost of this noninvasive therapy is significantly less. This cost decreases substantially when appropriate permanent magnets are applied directly to the site of injury.
It is accepted that pain control occurs via a series of integrated stages, each with particular objectives essential to the tissue/system repair processes. During the past 25 years it has been shown that magnetic fields offer an excellent possibility to be a non-invasive method of stimulation for pain management and control. A careful analysis of the successful application of MF for the control of pain with various origins can highlight the cellular and tissue components that may be plausible targets for MF action. Keeping in mind that the most important clinical principle of injury management is to provide a natural physiological environment for optimum healing, the proper choice of MF parameters may significantly enhance the healing process.
However, it should be recognized that basic science must create dosimetry and methodology for this type of stimulation. Saying that a patient was “magnetically stimulated” is as nonspecific as saying a patient was given a drug. Space does not permit more than a superficial presentation of evidence here to support the statement that “different MFs produce different effects in different targets under differing conditions of exposure” (Markov & Colbert, 2000).
Electric and magnetic stimulation have been proven to provide beneficial and reproducible healing effects, even when other methods have failed. In general, MF therapeutic modalities can be categorized in the following groups: (a) permanent magnetic fields, (b) low-frequency sine waves, (c) pulsed EMFs (PEMFs), (d) pulsed radio frequency (PRF), (e) transcranial magnetic stimulation, (f) millimeter waves.
Each of these groups has been successfully applied for various therapeutic procedures. This article will not discuss the publications on clinical application of the last two groups because they are not directly used for pain relief in the United States. Low-frequency sine waves and low-frequency PEMFs were used for the treatment of pain associated with rotator cuff tendinitis, multiple sclerosis, carpal tunnel syndrome, and periathritis. With the exception of periathritis—which reported no difference between treatment and control groups—all other targeted sources of pain received a reduction in VAS pain scores. More importantly, the improvement was observed in 93% of patients suffering carpal tunnel syndrome, and 83% in rotator cuff tendinitis. It also was reported that 65% of the patients who received daily treatment over 8 weeks for rotator cuff tendinitis were pain-free at the end of the study. In addition, 70% of the multiple sclerosis patients who received 15 treatments with low-frequency sine wave EMF reported a reduction in spasticity, improvement of bladder control, and improvement in endurance.
Neuromuscular electric stimulation was shown to be more effective when applied in combination with short magnetic pulses, with peak amplitude of 1.5 T for reduction of pain in arterior cruciate reconstruction. It also has been demonstrated that a 27.12 MHz PEMF makes the use of TENS for treatment of low back pain significantly more effective.
It should be noted that the so-called Diapulse signal was successfully used for treatment of pain in a number of conditions related to soft tissues. This signal is based on 27.12 MHz sine wave signal used for deep tissue heating in respect to cancer therapy. When applied in a pulsed mode (65 sec pulse burst, 100–600 pulses per second, peak magnetic field of 2 Gauss) these EMFs do not produce substantial heating in the soft tissue, and the effects are attributed solely to the MF stimulation. In the available English language literature, one may find reports of application of 27.12 MHz PRF for treatment of migraine, chronic pelvic pain, neck pain, and whiplash injuries. In parallel with improvement after the injury, the authors reported a 35% reduction in pain for patients having migraine, accompanied by a significant reduction of occurrence of headaches. Even more impressive were results for treatment of neck and whiplash injuries. Neck pain was reported to decrease from 7.0 to 4.0 after 3 weeks of daily treatment with PRF, and to 2.0 after 6 weeks of treatment. For the whiplash injuries, VAS pain scores decreased from 6.75 to 3.75 after 2 weeks, to 2.5 after 4 weeks, and 1.5 after 12 weeks of daily treatment with PRF. A 50% reduction in use of pain medication also was reported in whiplash patients as a result of EMF treatment (Markov & Colbert, 2000; Detlavs, 1987; Brighton & Pollack, 1991; O’Connor, Bental, & Monaham, 1990).
Approximately 35,000 patients have been treated for pain and other ostheoarthritis symptoms with pulsed signal therapy (PST), mainly in Europe and Canada. The system includes a bed, a circular coil of either 11 or 22 inches in diameter, which delivers pulses of variable frequencies (in the range of 5–24 pulses per second), and magnetic fields of up to 2 mT. Several double-blind studies reported an 88% decrease in pain for knee ostheoarthritis after 18 sessions, 30 minutes daily, and the pain relief was present during the next month of follow-up.
A similar approach is applied when a therapeutic EMF (TEMF) is used for treatment of low back pain. This system also has a bed and an elliptical coil (14x22 inches) that delivers to the target area a pulsating magnetic field of up to 15 mT with a frequency of 120 pulses per second. Although preliminary, the results show a significant pain reduction (up to 33%) for patients with chronic low back pain.
Since the middle of the 1990s, permanent magnets have become a widely used tool for pain relief. Several recent studies reported reduction of pain in post-polio patients (up to 76%), fibromyalgia (up to 32%), peripheral neuropathy (up to 33%), and postsurgical wounds (37%–65%) (Markov & Colbert, 2000). It should be noted that several studies failed to obtain any effects when so-called bipolar magnets were used. Reviewing recently reported diverse effects, we concluded that the failure to find any effect is an obvious result of the studies’ inaccurate dosimetry and poor planning.
The confusion with respect to the application of these modalities is because of the variety of methods of stimulation, parameters of the applied fields and current, and lack of a defined dosimetry. Therefore, a systematic study of EMF action on any particular biological system has to consider the following parameters: type of field, intensity or induction, gradient (dB/dt or dE/dt), vector (dB/dx or dE/dx), frequency, pulse shape, component (electric or magnetic), localization, time of exposure, and depth of penetration. The dosimetry requirements must be applied at the target site. In other words, it is not so important what the manual says for the field generated by the coil or the magnet. When the protocol refers, for example, to 15 mT MF, it should be considered as the MF at the target site, not at the surface of the generating system (Markov, 1994).
Consequently, any magnetic stimulation starts with identification of the desired target tissue and the MF parameters to be delivered to this tissue. Evaluation of the efficacy of EMF modalities should be based on recognition of the clinical problem, identification of the physiological responses, and a critical review of the reported basic science and clinical data. The ability of MFs to modulate biological processes is determined first by the physiological state of the tissue, which establishes whether a physiologically relevant response can be achieved and, secondly, by achieving effective dosimetry of the applied MF at the target site. The therapeutic effect depends on the spatial distribution of MF and induced current in the injured site, which is determined by tissue dielectric parameters (e.g., conductivity, permittivity).
It should be noted that there are significant differences between electric field/current and MF stimulation. Electric stimulation requires electrodes. Electrode size, spacing, and polarity are the most critical factors in the delivery of an adequate stimulating current. Closely spaced, small electrodes generally make the effective area of stimulation rather superficial due to the lower impedance of the current path through proximal tissue. The actual current density at any particular point within the tissue will depend on tissue composition and geometry and will change as these quantities vary during healing. The conduction of electrical current through biological tissues occurs as a result of the movement of charges along specific pathways. This charge transfer might result in electrothermal, electrochemical, and electrophysical effects (depending on the type of electrical current) and can occur at the membrane, cellular, or tissue level immediately after applying the voltage. The direct response usually results in a multitude of indirect cellular reactions that subsequently may alter further steps in biochemical and physiological pathways. A further complication of electrodes relates to potentially toxic electrolysis products, particularly if the electrode is placed inside the wound (Markov, 1994).
MF stimulation represents a significantly more effective approach to the healing process as an easy, inexpensive, and comfortable therapy. MF modalities do not exhibit the complications of contact electrodes because the fields are inductively coupled (i.e., immediate contact is not necessary to achieve the desired dose at the target tissue level). Thus, MFs can be applied in the presence of a cast or wound dressing because the MF applicator does not need to contact either the skin or the dressing.
Basic science and clinical reports together indicate the potential benefit of using permanent MF in pain management. Theoretically, the beneficial effects can occur by direct interactions of MF with important biological molecules and structures, or by indirect mechanisms involving mainly signal-transduction pathways. One should not forget the importance of nerve regeneration in injured tissues, which is also a subject of magnetic stimulation.
MFs and EMFs are still not widely popular treatment modalities. One of the main reasons could be the absence of a recognized common mechanism for EMF bioeffects. MF is, in principle, capable of inducing selective changes in the microenvironment around and within the cell, as well as in the cell membrane. Therefore, MF might be a practical method for inducing modifications in cellular activity, which in turn may correct selected pathological states. Assuming that the exogenous signal can be detected at the cell or tissue level, the biophysical mechanism(s) of interaction of weak EMFs and MFs with biological tissues, as well as the biological transductive mechanism(s), remain to be elucidated. Some specific reactions and processes in different biological systems suggest that most of the observed bioeffects strongly depend on the parameters of the applied electromagnetic fields.
The study of biophysical mechanisms is of great importance because it examines the nature of the initial interaction of EMFs with biological systems, and the expression of these changes as a biological response. Starting from the cell size and shape, going through the composition and architecture of the cellular membrane, one can also take into account the different sensitivity of cells based on the previously described characteristics. The cell membrane is most often considered the main target for EMF signals. The cell membrane could be the site of interaction of low-level MFs and EMFs by altering the rate of binding of calcium ion to enzyme and/or receptor sites. Any change in the electrochemical microenvironment of the cell can cause modifications in the structure of its electrified surface regions by changing the concentration of a specifically bound ion or dipole that may be accompanied by alterations in the conformation of molecular entities (such as lipids, proteins, and enzymes) in the membrane structure. Therefore, even small alterations in transmembrane voltage could trigger a significant modulation of cell function (Bassett, 1994; Markov & Colbert, 2000; Markov, 1994; Blank, 1993).
The examination of the signal transducing pathways seems to be a very important problem in studying reactions of living systems to any EMF. Most of the signal transduction pathways offer the enzymatic amplification of EMF stimulus into measurable cellular responses at the level of the second messenger. The cell cycle is equally important for the cell response: Is the cell differentiating, resting, or synthesizing new building components? When cells are organized in a tissue, the expected response also should include cell-cell communications (mainly via gap junctions). The proper conduct and analysis of in vivo experiments requires an awareness of the complexity of the animal/human organism and the existence of compensatory mechanisms that work on the organism level.
A series of studies on the influence of EMFs on various biological systems demonstrated the appearance of “windows” effects. The “windows” represent such combinations of amplitude and frequency (or other parameters of applied signal) within which the optimal response is observed, and once outside this range the response is significantly smaller. In other words, this demonstrates the principle “more does not necessarily mean better.”
The abundance of experimental and clinical data that demonstrates that exogenous MFs and EMFs of surprisingly low levels can have a profound effect on a large variety of biological systems is a serious indication that MF/EMF therapy could be a useful modality for pain relief.
Bassett, C.A.L. (1989). Fundamental and practical aspects of therapeutical uses of pulsed electromagnetic fields (PEMFs). Critical Review of Biomedical Engineering, 17, 451–529.
Bassett, C.A.L. (1994). Therapeutic uses of electric and magnetic fields in orthopedics. In D. Karpenter, S. Ayrapetyan (Eds.), Biological Effects of Electric and Magnetic Fields (pp. 13–48), San Diego: Academic Press.
Blank, M. (Ed.). (1993). Electricity and Magnetism in Biology and Medicine. New York: Plenum Press.
Brighton, C., & Pollack, S. (Eds.). (1991). Electromagnetism in Medicine and Biology (p. 365). San Francisco: San Francisco Press.
Detlavs, I. (Ed). (1987). Electromagnetic Therapy in Traumas and Diseases of the Support-Motor Apparatus. Riga: Zinatie.
Markov, M.S. (1994). Electric current and electromagnetic field effects on soft tissues, Wounds, 7, 143.
Markov, M.S., & Colbert, A.P. (2000). Magnetic and electromagnetic field therapy. Journal of Back and Musculoskeletal Rehabilitation, 14, 1–13.
O’Connor, M.E., Bental, R.H.C., & Monaham, J.C. (Eds.). (1990). Emerging Electromagnetic Medicine. New York: Springer Verlag.
