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Laser therapy no better for back pain than weak red light

PainSci » bibliography » Guimarães et al 2021
updated
Tags: lasers

PainSci commentary on Guimarães 2021: ?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

This is a high-quality trial published in the journal *Pain*. Unlike so many studies in this field, it was designed to *actually* answer the question — big enough and good enough. Nothing’s perfect, but this one has a lot going for it. The placebo control used here was particularly ideal, and a bit amusing: fake lasers are a fine sham.

Guimarães et al compared laser therapy to a premium placebo in 148 Brazilians with chronic unexplained low back pain. Pain and disability were tracked for a year, plus some secondary measures. Patients got a dozen treatments over a month. Half received real laser therapy, and the other half got… some red light!

The sham device was the same device as the real one, just with the business end disabled, not emitting a therapeutic dose — just one low-powered red light. Laser therapy doesn’t feel like anything, so there was simply no way for patients to know whether they were getting real lasers or not. The quality of the placebo is so important to this study that I’ll quote their description in full:

In the PBMT device used, the only visible diode is the red one. For the placebo treatment, 905 nm laser diodes and the 875 nm LED diodes were deactivated (turned off), and the power of the 640-nm LED diodes were turned down to 1 mW (mean power for each diode) to keep the visual aspect of red light, but not to deliver an effective therapeutic or considerable dose according the current available evidence.

(Funny that the authors felt it was necessary to clarify “deactivated” with the parenthetical “turned off.” Of all the jargon in this paper, *that* was the term that needed definition?)

The researchers used lasers the WALT way, using frequencies and intensities recommended by the World Association of PhotobiomoduLation Therapy.

So what happened? What any reasonably savvy cynic would expect: there was no important difference between real laser therapy and the fake stuff. More specifically, there was no clinically important difference in pain intensity, general disability, or any secondary outcome after one, three, six, or twelve months.

Yes, there was a slight boost in “global perceived effects” at one month for the lasered folks. Laser therapy advocates will point to this single data point and declare victory. But it’s just a moderate, temporary, short-term benefit for a rather squishy secondary way of measuring the effect of therapy — and it’s entirely possible it would vanish if you did the whole study all over again.

This is a rare case when I think the quality and credibility of the journal is noteworthy.

Most studies of laser therapy have been published in obscure and junky little journals. This one really stands out… and, as I hoped it might, the trial itself really ticks all the right boxes. Unlike so many studies in this field, it was designed to *actually* answer the question — big enough and good enough. Nothing’s perfect, but this one has a lot going for it.

One good example of the quality of the trial is that, delightfully, it was “prospectively registered” — which means that they declared in advance what they were up to (which makes it harder to fudge things later; p-hacking is harder when you’ve put all your cards on the table in advance).

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Photobiomodulation therapy (PBMT) has been used in several musculoskeletal disorders to reduce pain, inflammation, and promoting tissue regeneration. The current evidence about the effects of PBMT on low back pain (LBP) is still conflicting. We aimed to evaluate the effects of PBMT against placebo on pain intensity and disability in patients with chronic nonspecific LBP. This was a prospectively registered, randomised placebo-controlled trial, with blinded patients, therapists, and assessors. The study was conducted on an outpatient physical therapy clinic in Brazil, between April 2017 and May 2019. A total of 148 patients with chronic nonspecific LBP were randomised to either active PBMT (n = 74) or placebo (n = 74). Patients from both groups received 12 treatment sessions, 3 times a week, for 4 weeks. Patients from both groups also received an educational booklet based on "The Back Book." Clinical outcomes were measured at baseline and at follow-up appointments at 4 weeks, 3, 6, and 12 months after randomisation. The primary outcomes were pain intensity and disability measured at 4 weeks. We estimated the treatment effects using linear mixed models following the principles of intention-to-treat. There was no clinical important between-group differences in terms of pain intensity (mean difference = 0.01 point; 95% confidence interval = -0.94 to 0.96) and disability (mean difference = -0.63 points; 95% confidence interval = -2.23 to 0.97) at 4 weeks. Patients did not report any adverse events. Photobiomodulation therapy was not better than placebo to reduce pain and disability in patients with chronic nonspecific LBP.

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