An abstract presented at this year’s American College of Veterinary Internal Medicine reports on a study hypothesizing that low level laser therapy would shorten recovery times in dogs having back surgery for ruptured intervertebral disks and hind limb paralysis.
C.C. Williams; G. Barone. Is Low Level Laser Therapy an Effective Adjunctive Treatment to Hemilaminectomy in Dogs with Acute Onset Parapleglia Secondary to Intervertebral Disc Disease? Proceedings, American College of Veterinary Internal Medicine Forum, Denver, CO. June, 2010.
I’ve reviewed the evidence for cold laser therapy before, and it is generally of low quality and mixed. Overall, it is possible this therapy could have beneficial effects, but it is far from convincingly demonstrated at this point.
I would have expected this small study to find positive results. Of course most studies do regardless of the truth of the underlying hypothesis, which is why preclinical evidence and replication are so critical to effective evaluation of medical interventions. And unfortunately, many investigators and journal editors are reluctant to publish negative results, even though these are the most useful results. So I give these authors great credit for having the intellectual integrity to publish results that do not support their original hypothesis. That is how good science should be done. (Of course, they conclude by suggesting that the negative results were merely an artifact of the small size of the study not truly evidence that their hypothesis was incorrect. Such attempts to put the most positive possible spin on negative results are ubiquitous and probable unavoidable, so that shouldn’t be held against them).
The study involved 17 dogs with naturally occurring disease, ruptured intervertebral disks leading to partial or complete hind limb paralysis. All dogs had surgery (hemilaminectomy). They were divided into a group that also received 4 days of laser therapy following surgery and a group that did not. It is not clear if this allocation was random, or if there were any significant differences in the composition of the two groups. These are very important factors in evaluating the meaning of the results.
There is also no mention of any blinding, placebo control, or other attempt to control for possible bias beyond utilizing the same pain medication protocol for both groups. This significantly raises the risk of bias in the study. Such bias would almost certainly favor a positive result.
In any case, the investigators found no difference in recovery time between the two groups. Given the limited bias controls in the study, this is a bit surprising. Certainly, this small study cannot be taken as definitive regardless of the results. But it is one more bit of evidence to consider in the overall evaluation of the possible uses of cold laser therapy, and a bit which shifts the balance slightly in the negative direction.
Update: After this post was published, I became aware of a second, very similar study with different results:
W.E. Draper; T.A. Schubert. Low Level Laser Therapy as an Adjunctive Therapy to Thoracolumbar Decompression for Canine Intervertebral Disk Disease.
This study followed 36 dogs with acute hind limb weakness or paralysis due to intervertebral disk rupture. These dogs were assigned by alternating allocation to receive standard surgical therapy and post-operative laser therapy or standard treatment only. There was, again, no blinding or placebo control. The outcome measure assessed was the average time until the dogs in each group could walk. Those dogs receiving laser therapy were ambulatory after an average of about 6 days, compared to about 12 days for those not in the laser treatment group.
These positive results conflict with those of the other study. Again, positive results are what I would expect from an unblinded and uncontrolled trial, so they must be interpreted cautiously. Though the outcome measure itself is appropriate, it can involve some subjective judgments, and without randomization, blinding, and placebo controls, it is impossible to be certain that the treatment and control groups did not differ in some relevant way other than the treatment under investigation.
So from the point of view of an evidence-based analysis of the preponderance of the data, these two studies do little to settle the question of what if any value cold laser therapy might have in intervertebral disk disease. Their different results may be due to differences in patient population, laser treatment technique, or some other factor that obscures the true benefit of laser therapy in the first study. Or, they may differ because the second study was subject to some uncontrolled bias that did not operate in the first. I any case, the question is still an open one, and hopefully as more evidence accumulates we will be able to answer it more clearly.