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STUDY: Real laser therapy no better than a red LED for back pain

 •  • by Paul Ingraham
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Weekly nuggets of pain science news and insight, usually 100-300 words, with the occasional longer post. The blog is the “director’s commentary” on the core content of a library of major articles and books about common painful problems and popular treatments. See the blog archives or updates for the whole site.

Photobiomodulation therapy (PBMT) is the use of light as a medical treatment, popularly known as laser therapy.

The big idea is that lasers can supposedly stimulate healing, a regenerative medicine effect, some kind of cellular jiggery pokery. It’s based mainly on the premise that we know that some cells respond to light (duh, that’s how eyes work). It’s quite a leap to assume that a thin slice of the electromagnetic spectrum is capable of stimulating healing. Laser therapy has always been a classic example of premature hype about a futuristic, “high-tech,” unproven therapy… so it’s news that there’s a new, high-quality trial published in the journal Pain.

The placebo used in this trial was particularly ideal. And a bit amusing.

A premium placebo

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 other 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 illuminating results

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.

Consider the source

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).

This isn’t the last word, of course

As always with laser therapy, it’s quite reasonable to wonder if fiddling with the dials might make an important difference, and the authors — who have some vested interests in laser therapy — urge further investigation of “the optimization of PBMT parameters.” And it’s hard to disagree with that.

But the counter-argument is simple: they used lasers the WALT way, using frequencies and intensities recommended by the World Association of PhotobiomoduLation Therapy.

What if the WALT way is the wrong way? That’s a huge problem for laser therapy. What are the odds that some other way is going to work well when the officially endorsed method is utterly ineffective? Even if a different dosage is eventually proven to work rather well, that would also mean that the experts at WALT got it hopelessly wrong up to that point… and laser therapy as we know it today is based on guessing, not evidence.

Which is, in fact, precisely the case.

WALT’s mission? “To stimulate high quality research in photobiomodulation…” They got that in this case — arguably for the first time. Be careful what you wish for, WALT!

Guimarães LdS, Costa LdC, Araujo AC, et al. Photobiomodulation therapy is not better than placebo in patients with chronic nonspecific low back pain: a randomised placebo-controlled trial. Pain. 2021 06;162(6):1612–1620. PubMed 33449509 ❐ PainSci Bibliography 52147 ❐