I have been covering the subject of low-level, or “cold” laser treatment for many years. While there is some plausibility to the idea that laser light might have beneficial effects on tissue, very little convincing evidence of actual benefits in real patients. This is not surprising since the majority of good ideas that look promising on paper or in the lab fail to ever turn into safe and effective clinical treatments. Real life is more complicated than the research lab.
There have been very few clinical trials in dogs and cats, and most have had significant methodological limitations, so we can’t have much confidence in their findings. These findings, such as they are, have been mixed, with little consistent or compelling evidence of real-world benefits.
While this doesn’t mean lasers can’t be useful, it does mean that claims made for them by proponents, and the widespread use for many problems in dogs and cats, are based primarily on theory and anecdote, not on reliable research evidence. For something that is promoted as a dramatic breakthrough and is heavily marketed and widely used, it is surprising that it has been so difficult to actually demonstrate the supposedly amazing benefit in controlled research.
Another study has recently been published which follows up on the laboratory research suggesting laser might improve healing of bone and soft-tissue wounds. This is a well-conducted study with a reasonable number of patients, good control for bias and error (randomization, blinding, placebo controls, etc.), and reasonably reliable outcome measures. To steal my own thunder, it doesn’t look very good for laser therapy.
Renwick SM. Renwick AI. Brodbelt DC. et al. Influence of class IV laser therapy on the outcomes of tibial plateau leveling osteotomy in dogs. Veterinary Surgery. 2018: epub before print.
About a hundred dogs undergoing a TPLO (a common orthopedic surgery for cruciate ligament disease) were randomly assigned to receive laser treatments or placebo laser after the procedure. Though it’s not entirely clear if the people conducting the actual treatment were blinded to whether they were giving actual laser or placebo, everyone else (owners, surgeons, staff reading x-rays, etc.) appears to have been. The study used a couple of questionnaires to evaluate owners’ perceptions of comfort, function, and wound healing and had a surgical specialist evaluate the healing of the cut in the bone made as part of the procedure. Overall, none of these outcome measures showed any difference between real and fake laser treatment.
A subset of one questionnaire, looking at gait, did show a statistically significant difference between the treatments. This is not surprising since it is common for at least one outcome measures compared to show a statistical difference between treatments when many things are measured and compared. However, without a consistent pattern of such difference across outcomes, and with the difference in this particular measure being so small it is doubtful that it would be meaningful to the patients in terms of their comfort or function, the study provides pretty strong evidence against any value of laser therapy in these patients.
The authors, not surprisingly, emphasize the one small difference seen and suggest this might provide at least “mild clinical justification” for using lasers in patients undergoing TPLO. Personally, I think it is more reasonable to view the difference as a statistical fluke and to emphasize the failure to find any benefit in all the other measures evaluated, as well as the failure to show strong results in other clinical trials. Of course, there are many different techniques for using laser therapy, and proponents can always claim any single negative study is only negative because the technique used wasn’t quite right. This is the kind of “Yes, but….” Argument that supports the use of a lot of therapies even when clinical trial results consistently fail to find benefits. It is a reasonable argument up to a point, but eventually the failure to find positive effects does begin to suggest that there are none to find.
Absence of evidence can be evidence of absence once we’ve tried hard enough and long enough to find support for a scientific hypothesis. I don’t think we have reached that point yet with cold laser, and I do think more research is justified. However, it would be worthwhile for veterinarians and animal owners to be mindful that all the time and money being spent on laser treatment has so far not been proven worth it by good research, and in fact the balance of the evidence is not that encouraging.