Unique Use of Near-Infrared Light Source to Treat Pain

Pilot study using cosmetic device shows promise in reducing musculoskeletal pain in the foot, ankle, wrist, and knee joints.
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Debilitating foot and ankle pain are the bane of many patients. The sufferer often restricts their activity, limits exercise, changes their footwear, and seeks multiple remedies, often without reducing their symptoms. Decreased activity/exercise can result in weight gain and added burden on the foot. The causes of foot and ankle pain are numerous, with many treatments offering varying degrees of invasiveness and effectiveness.

One potential less-invasive treatment option is the use of low-energy light. Low-energy lightwaves have been used successfully for 40 years to speed healing of wounds, decrease pain, and decrease inflammation.1-19 This article evaluates the use of a near-infrared (IR) light source (StarLux-IR Deep Dermal, Fractional Heating from Palomar Medical Technologies, Inc., Burlington, Massachusetts) in ameliorating non-fracture foot and ankle pain (see above image).

Study Design
Forty patients with acute and/or chronic foot (n=36), ankle (n=1), hand/wrist (n=2), or knee (n=1) pain underwent between 1 to 10 treatments with the near-IR device. The time interval between treatment sessions was variable and determined by patient availability. Treatments were ended when a patient was pain free or had significant pain reduction, or when the patient simply decided to stop.

The device produces a non-coherent light source that was developed as a “skin-tightening” cosmetic device with output wavelengths of 850 to 1,350 nm and contact cooling (See Glossary of Terms, page 47). For this study, it was used at its lowest setting, 2.5-second pulse and fluence of 30 J/cm2. The device has aggressive contact cooling and will not fire or will stop firing if good skin contact is not maintained. Thin contact oil is used on the treated area of skin as a coupler for the contact cooling and for better light transmittance. Non-overlapping pulses were used, but for each treatment session multiple passes were performed, usually 3 or 4.

Patients were followed for up to 9 months. Conditions treated included acute and chronic non-fracture musculoskeletal injuries, plantar fasciitis, tendonitis, shin splints, acute hand and wrist sprain, carpal tunnel syndrome, and chronic knee injury pain. Pain assessment used the Wong-Baker FACES Pain Rating Scale, a subjective patient pain assessment conducted before and after each treatment using a scale of 0-5 (5 being worst).20 Pain reduction was deemed as the percentage reduction from baseline on this scale.

Seven patients were treated only with the IR device. Thirty-three patients had other treatment modalities before the course of near-IR treatments. Previous treatment modalities were only partially effective and in most cases these treatment modalities had been used for months. All other treatment modalities were stopped seven or more days before the commencement of near-IR treatment except for non-steroidal anti-inflammatory drugs (NSAIDs; n=8), which had been ineffective monotherapy prior to the near-IR.

The IR treatments were not covered by insurance and patients paid separately for each treatment.

Results
All but one patient reported a significant decrease in pain, ranging from 40% to 100% reduction. In most cases, the pain reduction started within hours after the first treatment (34 patients) or second near-IR treatment (39 patients) (Figure 1 and Table 1, pages 40-41). Two patients had significant pain reduction two weeks after the first treatment, but dropped out of the study.

Pain reduction appeared to be long lasting. Weeks and even months later, all patients with pain reduction were still either pain free or had markedly reduced pain. Many were able to return to exercise or wearing high heels. No complications occurred during or after any treatment. No patient stopped treatment because of discomfort during treatment.

Discussion
Low-level visible light has been used safely and effectively for more than 40 years to decrease pain, reduce inflammation, and promote tissue regeneration.1-19 The mechanism of “photobiostimulation” by low-level visible and/or IR “light” is still not completely resolved and higher-level irradiation can have the opposite effect at the same wavelength—a biphasic dose response.5 Near-IR wavelengths have been shown to accelerate wound healing in fibroblast cell cultures, without measurable temperature change.8

Numerous parameters can influence the efficacy and safety of “phototherapy.”5 Results can be evaluated with various objective and subjective parameters. More fluence can be better or worse depending on the condition being treated and confounding factors. Although, by definition, fluence = J/cm2, the identical fluence may be the product of a short pulse and high intensity or a long pulse and lower intensity—the effects may be very different.In our choice of the near-IR for an off-label use, we had a reasonable expectation that it might be beneficial for pain reduction and even facilitation of healing based on photobiostimulation-type effects of these wavelengths.5 We expected and found no complications at the low setting used.

The near-IR laser was developed for and approved by the FDA as a skin-tightening device through soft tissue coagulation and collagen remodeling. Typical treatment parameters for skin tightening are 10-second pulse duration and fluence of 60 to 120 J/cm2. The near-IR spectrum has an expected penetration depth shown in Figure 2. About 1% of the light is present at a depth of 3 cm.21-23

Cosmetic treatment parameters are very different from the use of the near-IR in this study, in which it was used at its lowest setting, 2.5-second pulse and fluence of 30 J/cm2. For pain reduction, the areas of injury being treated may be more than 1 cm deep, but the effect we need is not based on heating and thermal injury, so for this effect minimal penetration, with minimal light intensity, may not only be sufficient, but desirable. Although the optimal setting and wavelengths are to be determined, it is reasonable to expect that a very low fluence might be sufficient.2,5,9,10,15-17 The expected fluence at the required depths to decrease inflammation, decrease pain, and possibly speed healing in the affected areas was hoped to—and based on the results appears to have been sufficient to—at least decrease pain, with a significant reduction in pain scores seen in all but one patient.

While it is simple to maintain good contact between the device and the skin surface on flatter and padded areas of the body, the flat contact surface of the hand piece is less congruent in curved areas with less soft tissue such as a bony protuberance as on the back of the hand. In these cases, additional care must be used; the device has an attachment that blocks the light from one half of the hand piece, facilitating contact in difficult areas.

First published on: March 31, 2012