I love to watch TV reality shows about veterinarians. There are quite a few of them now; my favorite is “The Incredible Dr. Pol.” I learn a lot from them. For instance, I have learned that “polio” in goats means a vitamin deficiency disease, not the infectious disease that humans get. And I have learned that dogs don’t have blood types, so any dog can donate blood to any other dog. Nice to know. But as a skeptic, there are a few things on those shows that I question. I have frequently seen TV veterinarians use laser therapy to speed wound healing from both injuries and surgical incisions. I kept wondering “Is that for real?” Is it based on superstition or science? So I decided to look into the evidence.
What are lasers?
“Laser” stands for “light amplification by stimulated emission of radiation.”Einstein established the theoretical foundation in a 1917 paper, and the first laser was built in 1960. Lasers emit coherent light that can be tightly focused and can have a limited spectrum, emitting a single color of light. Output can be continuous or pulsed. A laser that produces light is technically an oscillator rather than an amplifier, and it has been suggested that the acronym LOSER, for “light oscillation by stimulated emission of radiation,” might have been a more correct acronym.I can see why that didn’t catch on! Today, lasers are everywhere; they have many applications, from bar codes to laser printers, from DVD players to laser pointers (great for giving lectures and for playing with cats), from surgery to welding, from entertainment to law enforcement. There are many types of lasers; they can use visible light or other electromagnetic frequencies, from infrared to X-rays and even gamma rays.
Lasers have many applications in medicine. In surgery, they can cut more precisely than scalpels and can stop bleeding. In cancer treatment, they have various uses that are supported by good scientific evidence. The evidence is not so clear for low-level lasers (cold lasers), which have been used for wound healing, smoking cessation, tuberculosis, temporomandibular joint (TMJ) disorders, carpal tunnel syndrome, fibromyalgia, osteoarthritis, rheumatoid arthritis, and much more. Cold lasers are even applied to mythical acupuncture points as “laser acupuncture.”
Lasers are widely used by veterinarians to facilitate wound healing, reduce inflammation, and treat musculoskeletal pain. Some veterinarians advocate laser treatment of allergic skin disease, infections, and envenomation; some claim they improve general health and enhance immune function and can even reverse “Qi-stagnation,” whatever the heck that might be! Veterinary studies are sparse, poorly designed, and the results are inconsistent. There are no systematic reviews of clinical trials validating laser therapy for specific indications in animals.[i]
A correspondent in Kentucky tells me his veterinarian pushes laser therapy for animals with sore joints, charging $240 for five treatments. Each treatment lasts 10 minutes. He says his dog hates going to the vet, and he wonders if there aren’t better ways to apply heat at home for longer periods.
Evidence in humans
There are far more studies in human medicine than in veterinary medicine. Hundreds of systematic reviews are available for specific conditions, but the results are inconsistent. In vitro studies demonstrate effects on tissues, and there are anecdotes galore, but the clinical studies in humans are far from convincing.
Stephen Barrett reviewed low-level laser therapy (LLLT) devices on Quackwatch.[ii]More than 40 of these devices have been cleared by the FDA under the Class II description of “lamp, non-heating, for adjunctive use in pain therapy” and as infrared heat lamps.
Dr. Barrett concluded:
“The scientific consensus is that no LLLT has been proven more effective for pain than standard forms of heat delivery. Some benefits have been reported, but the studies have been too small and/or too short to draw firm conclusions. The best-designed study of diabetic patients with sensory nerve impairment of the feet found that 90 days of Anodyne therapy at home brought about no more improvement in peripheral sensation, balance, pain, or quality of life than sham therapy.”
He reported various government enforcement actions against manufacturers for illegal marketing claims; in one case, three individuals pleaded guilty of conspiracy and went to prison. Several insurance companies including Aetna, CIGNA, and The Center for Medicare and Medicaid Services have reviewed the published evidence and explained why they don’t cover LLLT.
Aetna considers class III laser and high-power class IV laser therapy experimental and investigational for a long list of indications because there is inadequate evidence of effectiveness.[iii]They provide an exhaustive (and exhausting!) description of all the relevant published studies. They report research on everything from carpal tunnel syndrome to knee osteoarthritis, from hair loss to obesity. A typical excerpt:
“Although the results from large, uncontrolled, open trials of low-energy lasers in inducing wound healing have shown benefit, controlled trials have shown little or no benefit. The analgesic effects of low-energy lasers have been most intensely studied in rheumatoid arthritis. Recent well-designed, controlled studies have found no benefit from low- energy lasers in relieving pain in rheumatoid arthritis or other musculoskeletal conditions. Furthermore, although positive effects were found in some earlier studies, it was not clear that the pain relief achieved was large enough to have either clinical significance or to replace conventional therapies.”
CIGNA concluded[iv]“Low-level laser therapy (LLLT) has been proposed for a wide variety of uses, including wound healing, tuberculosis, and musculoskeletal conditions such as osteoarthritis, rheumatoid arthritis, fibromyalgia and carpal tunnel syndrome. There is insufficient evidence in the published, peer-reviewed scientific literature to demonstrate that LLLT is effective for these conditions or other medical conditions. Large, well-designed clinical trials are needed to demonstrate the effectiveness of LLLT for the proposed condition.”
The Centers for Medicare and Medicaid Services issued a Decision Memo[v]saying “CMS has determined that there is sufficient evidence to conclude that the use of infrared devices is not reasonable and necessary for treatment of Medicare beneficiaries for diabetic and non-diabetic peripheral sensory neuropathy, wounds and ulcers, and similar related conditions, including symptoms such as pain arising from these conditions… [therefore] The use of infrared and/or near-infrared light and/or heat, including monochromatic infrared energy (MIRE), is not covered for the treatment, including symptoms such as pain arising from these conditions, of diabetic and/or non-diabetic peripheral sensory neuropathy, wounds and/or ulcers of skin and/or subcutaneous tissues in Medicare beneficiaries.”
The research is marred by inconsistency. The studies use different kinds of laser, different devices, different powers and wavelengths, different treatment protocols, and a variety of different indications. There are both positive and negative studies, and no replications to confirm results.
Are class 4 lasers better?
Therapeutic lasers are classified as class 1 to class 4 depending on their potential for injury to eyes and skin.[vi]A watt is a unit of power defined as 1 joule per second; it is used to quantify the rate of energy transfer. Class 2 lasers produce 0-1 milliwatts, Class 3B lasers produce 5-500 milliwatts, and Class 4 lasers produce greater than 500 milliwatts. For comparison, the lasers used in surgery for cutting and cautery use up to 300 watts, which is 300,000 milliwatts.
Class 4 lasers were designed for surgical applications, not for therapeutic use. They heat the tissues, can burn the skin, and can cause permanent eye damage, even from indirect exposure. They can ignite combustible materials, starting a fire. Damage can be limited by increasing the beam diameter, turning down the power, and keeping the device in constant motion.
Manufacturers of class 4 devices who market them for therapeutic uses claim their devices work better because they use certain specific wavelengths, rapid pulses, and proprietary innovations.They are said to penetrate deeper into tissue (6 to 9 inches). A larger treatment head compresses superficial tissues, and a larger area of the body can be treated at once. They say the photons are absorbed by melanin, hemoglobin, oxyhemoglobin, and water. Energy generated by this process is felt as a soothing warmth. Light absorption stimulates cytochrome C to produce more ATP and free nitric oxide (a vasodilator) and reactive oxygen species. Growth hormone, cellular proliferation, and mobility increase. This improves blood circulation and speeds the healing process.
Marketers claim all this has been documented in the lab. Maybe, but others disagree,[vii]saying that 90% of the light energy is absorbed in the first centimeter. Even if the laboratory claims are true, that doesn’t mean there are significant clinical benefits to humans in the real world outside the lab. The evidence is lacking. There is no evidence that class 4 devices produce better clinical outcomes than class 3B devices.
The Richmar company, which sells 3B laser devices, has a webpage detailing “The Truth About Class 4 Lasers.”[viii]
- Longer wavelengths do NOT equal deeper tissue penetration.
- The higher power output could result in tissue damage
- They’re not a good fit for therapeutic use.
The LightForce website sells class 4 devices. They describe “5 Painful Conditions Laser Therapy Can Help When Nothing Else Works:”[ix]tendinitis, plantar fasciitis, arthritis, TMJ syndrome, and carpal tunnel syndrome. Maybe lasers can help, but they don’t provide even a shred of evidence. Why should we believe their bald assertions? As Christopher Hitchens said, ““What can be asserted without evidence can be dismissed without evidence.”
The bottom line
The use of therapeutic lasers by veterinarians and medical doctors is not warranted by the existing scientific evidence. As the Mayo Clinic says, “the question of whether these treatments offer hope, or are merely hype and hokum, is unanswered.”[x]
More research is needed.
This article was originally published as a SkepDoc column in Skeptic magazine.