Cold Lasers in Pain Management
Cold or soft laser therapy, also know as low level laser therapy (LLLT), is being used for an increasing number of medical and rehabilitative applications including pain management. The nomenclature alludes to the athermic or non heat producing characteristic of these FDA class 2 and 3 devices.1 Unlike hot lasers used to cauterize, vaporize, coagulate, or ablate tissue or tumors, cold lasers work through more subtle tissue effects that can result in the reduction of both pain and inflammation, devoid of tissue destruction. Consequently, cold lasers are finding a niche with soft tissue specialists of varying backgrounds including medicine, podiatry, dentistry and physical rehabilitation. Although a relatively new modality in the United States, cold lasers have been used in Canada, Europe and some parts of Asia for many years. Lasers fall under the general category of photomedicine, but this broader name often obscures the unique properties inherent with laser, properties which serve to distinguish this form of light therapy from other, perhaps less potent, forms of light energy.
In 2002, the FDA issued the first 510k premarket notification for a soft or cold laser device based largely on the strength of earlier large scale multi center clinical trials that had examined the effectiveness of cold lasers in the primary treatment of carpal tunnel syndrome. The GM study, as it has come to be known by, was arguably, the pivotal investigation that “tipped” the scale in favor of FDA approval for these devices. Since then, a number of laser manufacturers have followed suit with their versions of the ideal lasing device. To date, all these devices have been under a specified power level of 1 watt (considered to be threshold for thermal effect) and usually between 5 and 100mW. As a point of reference, a laser pointer is approximately 2-3mW in power. Recently, FDA class 4 devices have been introduced into the marketplace with much higher average power levels than their class 2 and 3 counterparts. Typically seen in veterinary medical use, time will tell how these devices will add clinical utility to the already growing number of lasers in the marketplace.
While numerous studies utilizing cold lasers have been performed to date, many do not provide precise test parameters such as power density, treatment duration, wavelength and site of application — all essential information needed to replicate findings. Despite the currently limited amount of quality research supporting cold laser use, the number of double blinded, randomized and controlled clinical trials is growing, as well as the amount of empirical evidence gathered from the now daily use of these instruments across the country.
The two most important modes of light interaction with tissue during laser treatment is through absorption and scattering. This has been studied predominantly at the molecular and macro-molecular level. Absorption is considered to be a conversion of energy from light to another form. Tissue absorbing properties are dependent on their concentration of light accepting molecules such as amino acids, cytochromes, chromophores and water. Each of these interacts with light at specific wavelength ranges (bandwidths). Scattering also occurs during cold laser treatment and is considered to be a change in light propagation direction and thought to occur due to the varying shapes of biomolecules and varying tissue interface configurations. Depth of penetration is determined by tissue type and wavelength emitted by a laser system. Like other forms of energy used in clinical settings such as electricity, heat, and sound, there is significant energy attenuation of laser light as it passes through tissues. The critical measurement in laser dosimetry appears to be energy density, which is calculated by dividing the total energy delivered to an area by the area of irradiation and expressed as joules per centimeter squared (J/cm2).2 Among other lasing characteristics, the energy density should always be reported in clinical studies so replication is possible. Animal studies have typically cited radiant exposure levels of 3-4J/cm2, whereas in human studies, it is recommended that significantly higher levels of irradiation approximating 30J/cm2 are required to compensate for animal size and skin type differences.3
The general consensus among clinicians using LLLT for conditions having an inflammatory component is that significant benefits can be accrued by those patients treated with laser.
Clinical Applications of Low Level Laser Therapy
Arthritis. The arthritides (osteo and rheumatoid forms) have been a popular target disorder for researchers in the last decade of cold laser investigations. The results of several well designed randomized clinical trials have given clinicians good reason to be encouraged with this form of treatment. Cellular research has provided some possible mechanisms of action for these positive results including laser mediated increases in cellular proliferation,4 enhanced collagen synthesis,5 conversion of fibroblasts into myofibroblasts,6 increased osteoclastic activity,7 reduced inflammatory markers,8 increased lymphocyte response9 and stimulation of the electron transport system leading to enhanced ATP production.10 These putative mechanisms help explain the impressive results that laser therapy research has had to date in the area of wound healing. With the use of larger diameter cluster probes emitting beams of mixed wavelengths, clinicians can efficiently treat large wounds in short periods of time. Brosseau et al conducted a systematic review of the available literature examining the relationship between low level laser and arthritis in 2000.11 They applied an a priori protocol according to methods recommended by the Cochrane Collaboration. Their conclusions were that low level laser therapy (LLLT) should be considered for short term relief of pain and morning stiffness in rheumatoid arthritis. In regards to osteoarthritis, the same authors felt that a determination of effectiveness could not be made based on the available literature due to conflicting and lacking consistent dosage descriptors. The general consensus among clinicians using LLLT for conditions having an inflammatory component is that significant benefits can be accrued by those patients treated with laser. There have been some very promising clinical trials involving cold laser in both knee and cervical spine osteoarthritis as well.12,13