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Trials & Errors

Science is based upon trials and errors. Yes, even errors give serendipitous results; the discovery of penicillin is just one of them. Science starts with ideas, but has to be confirmed. Too often ideas are commercialized before there is any documentation.

One good idea seems to be Interferential laser therapy. This means that two probes are used simultaneously, for instance one in the front and one in the back of a shoulder. Sounds like a good idea: more energy into the area and arriving from two sites. Well, it still may be a good idea, but the first controlled trial failed to find any additional effect of the 2nd probe! Here is the paper in abstract:

Montes-Molina R, Prieto-Baquero A, Martínez-Rodríguez ME, Romojaro-Rodríguez AB, Gallego-Méndez V, Martínez-Ruiz F. Interferential laser therapy in the treatment of shoulder pain and disability from musculoskeletal pathologies: a randomised comparative study. Physiotherapy. 2012; 98(2):143-50.

BACKGROUND: Interference is an important feature of the waves. When two or more in phase light waves meet, a new and reinforced wave is generated. Shoulder pain is a common clinical problem and laser is one of the treatments frequently used to relieve it.

OBJECTIVE: To test the safety of interferential laser therapy generated by two independent low level lasers and compare its effectiveness with conventional single laser therapy in the reduction of shoulder musculoskeletal pain and associated disability.

DESIGN: Randomised and single-blind controlled clinical trial.

PARTICIPANTS: 200 patients with shoulder musculoskeletal pain were randomly assigned in two groups, 100 people each.

INTERVENTIONS: Group I, experimental (n=100) received interferential laser, placing two probes opposite each other over the shoulder joint. Group II, control (n=100) received conventional laser therapy, using a single probe along with a second inactive dummy probe. Lasers used were GaAlAs diode (810 nm, 100 mW), in continuous emission. Laser was applied in contact mode through ten sessions, on 5 shoulder points (7 Joules/point) per session.

MAIN OUTCOME MEASURES: visual analogue scale (VAS) score and shoulder pain disability index (SPADI), recorded before and after laser treatment.

RESULTS: There were no differences between both groups in the reduction of pain, either assessed by VAS scale (median difference=0, 95% CI of the difference = -.6 to .5, p = 0.81) or SPADI index (median difference = .4, 95% CI of the difference = -2.9 to 3.8, p = 0.80), using the Mann-Whitney U-test. Comparison between the scores recorded before and after the treatment, within each group, showed significant differences for VAS during movement (median difference=3, 95% CI of the difference = 2.07 to 4, p < 0.001) and SPADI index (median difference=3.5, 95% CI of the difference = 2.67 to 3.85, Wilcoxon test, p < 0.001), for both groups.

CONCLUSIONS: In this study, the application of two low level lasers in order to generate interference inside the irradiated tissue showed to be a safe therapy. Both interferential and conventional laser therapy reduced shoulder pain and disability. Nevertheless, differences between them were not detected. Future research in this field could include applying this technique with other laser parameters or application forms.

[NB. If one wishes to play with words, laser therapy could, in and of itself, be called ‘interferential’, in that the random interference of coherent light waves in the tissue results in the creation of a speckle field. However, attempting to ‘enhance’ this effect – as in the previously discussed study – by introducing additional light sources to irradiate the same volume of tissue, may decrease efficacy by reducing the contrast of the original speckle field, as hypothesised by Hode T et al (2009, 2011).]

Other ideas are commercialized upon wishful thinking or lack of knowledge. One such example is the combination of continuous wave 808 nm and pulsed 904 nm into one single probe. At first glance this looks like a good idea, but there are complications: Pulsed 904 nm is known to require lower energies than CW 808 nm, so the treatment of e.g. open wounds may become problematic, and overdosing may be a potential risk in some cases. And it is not obvious that two wavelengths always make 1 + 1 = 2. Still, it is an interesting idea, albeit not new.

The dark side of the commercialization of this type of probe is the claims made by the manufacturer. Read this:

“Continuous Laser emissions act fast on inflammation, stimulating blood and lymphatic circulation and inducing fast re-absorption of fluid build-ups; however, they only have a secondary effect on pain, which is diminished after reducing the inflammatory process.”

“Pulsed Laser emissions, on the other hand, have a practically immediate effect on pain, since they are able to induce analgesia, interfering with the very transmission of the pain impulse to the higher brain centers, but they are less effective at treating inflammation and oedema, only achieving results after a long period of application.”

Sadly, there is no scientific documentation behind these claims; actually, the weight of evidence would seem to support opposite argument: CW lasers have an excellent and immediate effect on pain (see Chow R et al 2009, 2011a, 2011b), inducing analgesia directly by interrupting the transmission of pain signals to the brain; and pulsed 904 nm lasers are fine for reducing oedema (see Lievens P 1989, Carati CJ et al 2003) and inflammation and, secondarily, relieving pain. In short, one could swap the words ‘Continuous’ and ‘Pulsed’ in the two sentences above and, arguably, produce a more accurately representative summary of the current evidence base. These are just a few examples disproving the extravagant claims of this manufacturer.

In war, truth is the first victim, they say. Why, then, in the marketing of therapeutic lasers, when the truth is good enough?