Focus on Alternative and Complementary Therapies
www.pharmpress.com/fact
Focus Alternat Complement Ther©2005 Pharmaceutical Press
Focus Altern Complement Ther 2008; 13: 11–3
The use of light to treat disease precedes written records. Acceptance and benefits relative to alternative treatments have fluctuated over the years, but it should be remembered that as recently as 1903 Finsen received the Nobel Prize as a result of his investigation into the effects of light on bacteria and, in particular, the bactericidal effects of ultraviolet radiation on cutaneous tuberculosis.
Early efforts emphasised light’s thermal and destructive aspects. More recent work, however, has taken advantage of the invention of the laser (Light Amplification by Stimulated Emission of Radiation) in 1960 and has emphasised its non-thermal and non-destructive capabilities. One of the more popular (but more controversial) applications of this movement is based on the belief that the appropriate application of light at intensities too low to cause measurable heating can alter cellular and tissue function. This approach owes its existence to work begun by Endre Mester in the mid- 1960s, which demonstrated the potential for stimulation of tissue repair mechanisms by laser light and emphasised a potential clinical benefit in the healing of diabetic ulcers. Research has continued to the present and although a number of terms are used [e.g. low level laser therapy (LLLT); laser biostimulation, laser therapy], all refer to the same concept and all stem from Mester’s pioneering efforts. Today this form of photoor light therapy has a clinical and research presence in many countries (for example, the modality is widely available in physiotherapy departments within the UK’s NHS) and is promoted as an effective treatment for a variety of conditions, ranging from slowly healing soft tissue wounds to pain.
LLLT involves the application of low power (i.e. generally < 500 mW) laser irradiation to alter cellular or tissue function. The terminology used to describe treatment varies considerably and, in addition to the terms noted above, may involve terms such as ‘cold’, ‘low intensity’, ‘low power’, or simply ‘laser therapy’. Each term has its strengths and weaknesses, but low intensity laser therapy (LILT)1 and low level laser therapy (LLLT)2 are probably the most common and the most preferred.
The first lasers were gaseous He—Ne devices; as a result Mester began his studies with these. These devices, as well as their soon to be available krypton, argon and noble gas counterparts, were expensive and limited in their capabilities. By the mid- to late 1980s, developments in laser technology permitted their replacement with smaller, cheaper and more durable laser and superluminous diodes. Two of these, the gallium—arsenide (GaAs) and the gallium—aluminium—arsenide (GaAlAs), remain the most commonly used components of today’s clinical treatment probes. Today’s probes frequently incorporate multiple diodes in the form of fixed or flexible arrays that permit the treatment of wider areas than would otherwise be possible. Although debate continues about the importance of the coherence of the beams of light produced by laser diodes, multisource units incorporating noncoherent superluminous diodes are less expensive and particularly popular in the treatment of musculoskeletaland sports injuries.3 Apart from the treatment applicator, controller units for contemporary light/phototherapy systems are highly sophisticated, typically with built-in computerised treatment protocols.
The key irradiation parameters that define a laser treatment may be described as follows. Wavelength is expressed in nanometres (nm), and for LLLT, wavelengths in the visible red and near infrared part of the spectrum are used. As absorption of light tends to increase with frequency, deeper-lying musculoskeletal conditions are often treated with longer, lower-frequency infrared (IR) wavelengths (i.e. 830nm and above), while the shorter wavelength, visible red (632.8 nm, 660nm, etc.) irradiation is more commonly recommended for the treatment of superficial wounds. Power output expressed in milliwatts (mW; compared with domestic light bulbs on the order of a hundred watts). LLLT by definition is designed to achieve its benefits in a way that is not dependent on tissue heating. In practice, this means that most applicators are limited to powers of <500mW and energy deliveries of <4Joules/cm2. Higher intensities obviously permit faster treatment and the issue of time and treatment intensity remains an area of active investigation and controversy. Attenuation is an issue: more consistent results in the treatment of musculoskeletal lesions have been reported with power outputs over 30mW. Dosage may be specified as energy (in Joules; J) or energy density (Joules per square centimetre; J/cm2). Dosages vary depending on the lesion to be treated. Open wounds typically receive dosages of 1–4 J/cm2; in contrast, deeper-lying musculoskeletal lesions are generally irradiated at higher skin intensities (>6–12 J/cm2) to take into account losses due to tissue attenuation. It should be noted that dosages reported in clinical studies vary enormously (from <1 to >50 J/cm2); however, positive results in musculoskeletal disorders are generally associated with use of dosages over 4J/cm2. In terms of waveform, treatment may be performed with irradiation that is delivered continuously at a fixed intensity [continuous wave (CW)] or pulsed [expressed in Hertz(H) or kiloHertz(kH) as appropriate]. Although claims are made for specific pulsing and frequencyspecific patterns, the evidence is inconclusive: positive and negative results have been reported for regimes using CW as well as low and high pulsing frequencies.
LLLT has the advantages of being non-invasive, easy to apply and relatively inexpensive. Safety seems to be of limited concern: adverse events are rarely reported and in theory should be minimal in an approach that, by definition, is non-destructive and does not produce significant tissue heating although it is almost always recommended that pregnant women and the growth plates of growing bones should not be irradiated. The lack of heating makes the therapy applicable during the acute stages of injury (in contrast with heating agents), and claims that it can both accelerate tissue repair and lessen pain makes its use particularly intriguing. While this has led to wide application, its limited evidence base and occasional promotion as a virtual panacea by adherents and some manufacturers has resulted in a persistent scepticism by some.
Treatment most commonly involves direct irradiation of the lesion or site of pain, typically with the applicator in contact with the skin, although in the case of open wounds a small separation is usually maintained. Irradiation, however, may also be applied to the (afferent) nerves innervating a painful area, as well as acupuncture, trigger and tender points.4 Laser therapy has also been used to irradiate lymph and blood vessels as an adjunct to stimulate cells involved in tissue repair and potentially lessen the consequences of lymphoedema.
The physiological and biological effects of LLLT have been extensively studied. The best evidence is found in the well-controlled world of the laboratory, where cells can be exposed to carefully controlled light intensities, wavelengths and durations. In fact, the majority of reported laboratory studies find effects on a range of cellular processes, from immunological function and protein synthesis to proliferation. There is evidence that 1–4 J/cm2 may be the most effective energy range and that the red—IR wavelengths used in practice are particularly effective. Studies that employ the more complex model of nerve and tissue cultures are also supportive. Unfortunately, the evidence becomes more difficult to interpret. Establishing benefits is most difficult at the level of the intact organism (whether human or not) and one is tempted to argue from a teleological perspective that the body resists treatment as a result of millions of years of trying to maintain homeostasis regardless of external stimuli. Clinical trials with enough power to provide definitive answers are difficult to perform and are limited in availability and generalisability. As a result, there are relatively few well-designed and executed RCTs on which to build a solid evidence base.5,6
Recent systematic reviews bear this picture out. Thus, while there is moderate evidence of LLLT treatment benefit in neck pain,789 rheumatoid arthritis,10 osteoarthritis of the knee,11 and carpal tunnel syndrome,12 there is much less for potentially promising areas such as stroke,13 urethral pain,14 temporomandibular dysfunction, 1516 and lymphoedema.17 While reviews in other areas of popular application have reported a reassuring lack of adverse events, there is insufficient evidence of benefit in male or female pattern hair loss,18 fibromyalgia, 19 wound treatment 20 or low back pain.21 The lack of comparison to alternative treatments such as ultrasound, heat, cold and massage makes the determination of clinically practical benefits even more difficult.
Evidence to support the use of light/laser is developing, but remains patchy and is hindered by a heterogeneity of methods, data reporting and conditions. Further work is necessary to definitively establish the optimal areas of clinical effectiveness and dosimetry of laser therapy. Given the potential benefits associated with this modality (i.e. accelerated tissue repair, relief of pain), this approach represents an area with considerable promise for future research.
