By Brennen McKenzie, MA, MSc, VMD, cVMA

Since the discovery of electricity and magnetism, these mysterious forces have been thought to possess healing powers. Many fanciful electrical devices were promoted in the 19^th and early 20^th centuries as cures for diverse ailments or general health tonics.¹ More serious scientific research into the effects of electromagnetic fields on tissues and animals began in the 1930s, and by the 1980s, there was sufficient evidence for some kinds of pulsed electromagnetic field (PEMF) devices to be approved by the U.S. Food and Drug Administration (FDA) for use in human patients.²

Since then, a large number of PEMF devices have been marketed for both human and veterinary medical use. The scientific evidence behind these devices—from in vitro and animal model studies to clinical trials—is complex and inconsistent. Pubmed lists about 50 systematic reviews covering nearly 200 clinical trials; there are well over 1000 articles if one includes preclinical laboratory studies.

PEMF devices use a variety of designs and treatment protocols for a wide range of medical conditions, so any generalizations about their efficacy are necessarily tenuous. However, because PEMF devices are aggressively marketed to veterinarians and animal owners, some assessment of the evidence behind them is necessary. 

Preclinical evidence

There is substantial scientific literature showing electromagnetic fields have interesting and potentially significant biological effects on animal cells and tissues. PEMF devices can affect the levels of calcium and nitric oxide in tissues, which can influence extensive and complex pathways involved in metabolism, inflammation, pain transduction, tissue growth and repair, and many other biological activities. PEMF devices also have been shown to affect gene expression, vasomotor tone, and many other physiologic processes.^2-5 These studies show the potential for clinically relevant benefits resulting from PEMF treatment.

Lab animal studies also show effects of PEMF treatment that may be useful to clinical patients, although there is great variation in the treatment used and the results. Some evidence suggests benefits in soft-tissue and bone healing, though not all the research is positive.^2,6-8

However, it is important to understand such in vitro and animal model findings are insufficient to justify clinical use. Many therapies—from pharmaceuticals to manual therapies to other high-tech treatments such as low-level laser—have demonstrable effects on tissues that often do not translate into meaningful clinical benefits for patients. Clinical trials are always necessary before making confident claims for any medical therapy. 

Human clinical trial evidence

Though there are hundreds of clinical studies in humans for PEMF in various indications, the results are mixed and difficult to interpret. For example, there are some studies showing meaningful improvements in postoperative pain in human patients undergoing breast augmentation surgery.^9,10 However, systematic reviews of studies evaluating PEMF for pain associated with osteoarthritis (OA) of the knee are mixed, with some showing no effect,¹¹ some inconclusive,^12-15 and others suggesting some benefit.¹⁶ Strong generalizations about the efficacy of PEMF for pain aren't justified based on literature incorporating varied treatment protocols for different indications with mixed results.

The same inconsistency exists in studies of bone healing^17-20 and other clinical uses in humans.^21-23 There is evidence of benefits, but it is inconsistent, and the strength of this data is limited by heterogeneity in treatment protocols and indications, as well as by methodological weaknesses in clinical trials.

As always, clinical trial evidence for specific indications in veterinary patients is the most relevant type of evidence for veterinarians choosing which treatments to adopt. The clinical trial literature for PEMF is currently very sparse, but there are some studies we can evaluate.

Veterinary clinical trials

Though some encouraging case studies and uncontrolled studies have been published,²⁴ there have been only a few controlled clinical trials of PEMF treatment in veterinary patients.

A small pilot study randomly divided 16 dogs undergoing ovariohysterectomy into four groups:

• IV saline;
• IV saline and PEMF;
• IV morphine; and
• IV morphine and PEMF.

For six hours after extubation, a variety of physiologic variables were measured, including heart and respiratory rates and blood pressure; a validated pain scale was employed by a blinded observer. Researchers noted a couple of statistical differences in blood pressure at some time points, but no identifiable analgesic effect provided by PEMF. The small number of animals in each group likely made the study underpowered to detect all but the most dramatic effects.²⁵

A 2018 study evaluated the use of a PEMF device in 16 dogs undergoing hemilaminectomy for naturally occurring intervertebral disk disease (IVDD).²⁶ Eight dogs were randomized to active or sham PEMF treatment and evaluated in terms of a primary outcome (gait) and numerous secondary outcomes involving neurologic status, function, and pain. There was no benefit detected in the primary outcome or in the majority of secondary outcomes.

Placing responses and mechanical sensory threshold at the surgical site did appear improved in the PEMF group compared to the control. However, when multiple secondary outcomes are evaluated in a clinical study, it is common for some differences to appear by chance despite statistical efforts to control for this²⁷ and the authors state these findings 'should be interpreted with caution.'²⁶

The most recent veterinary clinical trial also used IVDD patients as subjects.²⁸ Fifty-three patients were randomly assigned to active or sham PEMF treatment and evaluated in the hospital and by owners at home for up to six weeks following surgery.

There were no apparent benefits in terms of pain or function as assessed by owners or clinicians, though post-hoc power calculations indicated the study was not sufficiently powered to detect some of these differences. There were some small differences in long-term appearance of surgical wounds, although all wounds healed appropriately. Owners also gave slightly more pain medication to dogs in the control group than the PEMF group, though pain was not rated differently between the groups.

Conclusions

Despite the fact there has been interest in the potential medical applications of electricity for more than 150 years, and serious scientific research investigating PEMF has been going on for over 50 years, there is surprisingly little robust evidence showing meaningful clinical benefits. We know a lot about the physiologic effects of PEMF, and preclinical research suggests a number of clinical applications. There is clinical trial evidence from humans showing potential benefits for bone and soft-tissue healing, pain reduction, and other uses, but this evidence is inconsistent and complicated by the use of many different devices and treatment protocols. PEMF devices are widely used, which creates the impression they have been solidly validated, but the reality is more ambiguous.

There also is preclinical research in veterinary species showing physiological effects from PEMF devices and potential clinical applications. However, there are very few clinical trials of PEMF in actual patients. Published studies have not found consistent and convincing evidence of clinically meaningful benefits.

Many outcome measures show no effect of PEMF, though a few have shown effects that might be meaningful. If additional independent trials confirm such potential benefits, it may be possible to have confidence in some clinical uses of PEMF. For now, however, the marketing claims of PEMF manufacturers and the excitement of proponents far exceed the strength of the available scientific evidence.

It also is worth noting most studies of PEMF devices in human and veterinary patients have found few, if any, adverse effects. While this is reassuring, it also calls into question the real potency of these devices. Medical treatments with important and dramatic benefits that have no meaningful side effects are extremely rare. It is more common to find the absence of adverse effects indicates the lack of any meaningful clinical effects at all.

Brennen McKenzie, MA, M.Sc., VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists' opinions do not necessarily reflect those of Veterinary Practice News Canada.

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