Therapeutic Laser for the Treatment of Chronic Low Back Pain
I first discussed some of the important aspects of low back pain and the use of therapeutic laser treatment protocols in the January 2007 issue of Practical Pain Management.1 I am revisiting the subject of chronic low back pain in this article because of new information about the relationship between chronic pain and brain atrophy.2 Tracey and Bushnell are using relatively new, noninvasive neuroimaging and electrophysiologic technologies to study how both acute and chronic pain affect signal processing (functionality), metabolic activity, and structural changes in the human brain.3
To date, various chronic pain conditions have been investigated, and a common finding is that, at some undetermined point in time, there is a degeneration of gray matter volume and density in critical brain regions that may become irreversible. Related research during the past decade has uncovered 3 trends establishing chronic pain as a brain disease (see Table 1). It is hypothesized that this may be due to excitotoxicity and inflammatory processes that result ultimately in neurodegeneration.4
Low Back Pain
Low back pain continues to be epidemic, affecting 75% to 85% of all Americans at some point during their lifetime.5 The vast majority of acute low back pain is the result of injuries such as sprain or strain, whereas the cause of chronic low back pain is multifactorial.5 Chronic low back pain is defined as pain of more than 3 months’ duration. It occurs in 2% to 8% of those who experience low back pain.5
The exact causes of chronic low back pain continue to be a mystery. Recent scientific studies have implicated a number of chemical mediators as possible contributors to the production of chronic low back pain.6 These include:
- Pro-inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-10, and tumor necrosis factor (TNF)–alpha
- Prostaglandin E2 (PGE2)
- Nitric oxide
Patients with chronic low back pain may also have emotional factors, such as depression. Studies have shown that 62% of the patients treated at pain clinics for low back pain have some type of depression.7
There are a number of biochemical effects that have been observed with laser therapy/phototherapy.8,9 Several of these effects relate directly to the management of the patient with chronic low back pain. Three of the most prevalent features of patients suffering from chronic low back pain are inflammation, pain, and edema.6 Injured cells and tissues generate enzymes that encourage the receipt of photons more readily than healthy cells and tissues do. Primary photoacceptors, which are activated by light, are thought to be flavins, cytochromes, and porphorins.10-11
These photoacceptors are located in the mitochondria and can convert light energy into electrochemical energy. Chromophores, in the form of porphyrins, have been shown to play an important role. Small amounts of singlet oxygen have been shown to accumulate in tissues irradiated with laser light.8 Singlet oxygen affects the formation of adenosine-5’-triphosphate (ATP) in the mitochondria12-20 (see Table 2).
Research in laser and light therapy has documented that red and near infrared light reduce pain by a combination of these responses (see Figure 1).21-23
There are several neurologic responses to laser therapy that may influence brain recovery or prevent brain atrophy as well as several of the physiologic effects listed above. Oron et al studied the effects of gallium arsenide (GaAs) laser irradiation on ATP production in normal human neural progenitor (NHNP) cells.24 Tissue cultures were treated with the GaAs laser, and ATP levels were determined 10 minutes after laser application. The quantity of ATP in the treated cells was significantly higher than in the nontreated group. The application of laser to NHNP cells significantly increases ATP production (P<0.05). This may explain the beneficial effects of low-level laser therapy (LLLT) in stroked rats.24
Trimmer et al performed an in vitro study showing that a single, brief treatment with a gallium-aluminum-arsenide (GaAlAs) laser increased the velocity of mitrochondrial movement for 2 hours in cells taken from patients with sporadic Parkinson’s disease (PD).25 Treatment sped the velocity of mitrochondrial movement up to levels approximating those of disease-free, age-matched cells. Their findings provide early-stage confirmation that laser therapy has the potential to improve neuronal function in many patients with PD and other neurodegenerative diseases.25
Schiffer et al studied 10 patients with major depression. Each patient was given a baseline standard diagnostic interview, a Hamilton Depression Rating Scale (HAM-D), a Hamilton Anxiety Rating Scale (HAM-A), and a Positive and Negative Affect Schedule (PANAS).26 Patients were then randomly given four 4-minute treatments: near infrared (NIR) light radiation to left forehead at F3, to right forehead at F4, and placebo treatments (light off) at the same sites. Immediately following each treatment, PANAS was repeated, and at 2 and 4 weeks posttreatment, all 3 rating scales were repeated. At 2 weeks posttreatment, 6 of 10 patients had a remission (score ≤10) on the HAM-D, and 7 of 10 achieved remission on the HAM-A. Patients experienced highly significant reductions in both HAM-D and HAM-A scores following treatment, with the greatest reductions occurring at 2 weeks.
This small feasibility study suggests that NIR photobiomodulation (PBM) may have utility for the treatment of depression and other psychiatric disorders and that double-blind, randomized, placebo-controlled trials are indicated.26
Tissue Penetration and Saturation
Chronic low back pain is a complex clinical condition that involves many different tissue levels—from subcutaneous and muscle tissues to the deeper tendons and ligaments, including the intervertebral disc. Laser therapy, if it is to be effective, must be applied in a way that will produce significant biochemical changes in the superficial, medium, and deep tissues. Red light will affect the skin and subcutaneous tissue to an approximate depth of 1 cm. Infrared light will affect deeper tissue structures from 1 to 5 cm depth. Comprehensive laser/light therapy for treating chronic low back pain must therefore include the use of both red and infrared wavelengths.