Effect of Low-Level Laser Therapy on Incidence of Postherpetic Neuralgia

Because the increased cytokine levels in the acute phase of herpes zoster are assumed to be a potential mechanism for inducing PHN, the early suppression of these cytokines by LLLT may help prevent the development of PHN.

Low-level laser therapy (LLLT) may help to deactivate the herpes simplex virus, in turn reducing the incidence of postherpetic neuralgia (PHN).

Currently, no treatment exists that reduces the incidence of PHN, which typically affects adults aged 50 to 80 years old.

In this study, Yu-Tsung Chen, MD, of Wan Fang Hospital, Shuang Ho Hospital, and the College of Public Health and Nutrition, all in Taipei, China, and colleagues conducted a retrospective review of herpes zoster cases to evaluate the effectiveness of LLLT for the reduction of PHN incidence at acute and subacute stages of infection.

Overall, 304 patients with herpes zoster were identified, with 139 receiving LLLT and 165 patients serving as controls. Among those who received LLLT, 48 were classified as being in the acute stage, defined as the first 5 days after rash eruption, with another 48 classified as being in the subacute stage, defined as days 6 through 14 after rash eruption. The remaining 43 participants began LLLT treatment more than 14 days after initial rash eruption or received less than 3 sessions of LLLT.

Notably, there was no significant difference in zoster dermatome distribution among the 3 groups, with thoracic spinal nerves, trigeminal nerves, and the ophthalmic branch most often implicated.

One month after eruption, 27.3% of patients in the control group were diagnosed with PHN, while 8.3% and 22.9% of patients in the acute and subacute groups, respectively, developed PHN. Incidence of PHN was significantly different among the 3 groups (=.024), with incidence significantly greater in the control group (=.016). At 3 months after eruption, 14.3% of patients in the control group were still dealing with PHN, compared with 2.1% and 4.2% of the acute and subacute groups.

At 6 months post-eruption, no patients in the acute group had PHN, compared with 9.7% and 4.2% in the control and subacute groups. At this time point, there was still a significant difference in PHN incidence in the control group (=.047).

Further analyses revealed that application of LLLT at the acute stage resulted in lower PHN incidence at 1 month (odds ratio [OR] 0.21, P =.006, 95% CI 0.068–0.632), 3 (OR 0.112, P =.038, 95% CI 0.014–0.886), and 6 months (OR 0.123, P =.021, 95% CI 0–0.606) post-eruption compared with controls. This was also the case in the subacute group, though only at 3 months (OR 0.187, P =.032, 95% CI 0.041–0.865).

The authors noted that older age at time of eruption was associated with a greater incidence of PHN after 1 and 3 months, and that use of famciclovir did not appear to decrease PHN incidence in either the acute or subacute groups.

“This result might be explained by the anti-inflammatory effect, nerve regeneration, and indirect viral deactivation stimulated by LLLT,” the authors wrote. “In addition, LLLT has been demonstrated to decrease proinflammatory cytokine levels, such as tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, which play important roles in the pathogenesis of PHN.”

“Because the increased cytokine levels in the acute phase of herpes zoster are assumed to be a potential mechanism for inducing PHN, the early suppression of these cytokines by LLLT may help prevent the development of PHN,” the authors continued. “It may also explain why early application may reduce the incidence of PHN but is less effective in the subacute group.”

The authors recognized that a placebo effect is a substantial concern in this study due to the fact that it was retrospective and not a double-blind randomized controlled trial; however multivariate analysis revealed a significantly lower PHN incidence only in the acute group, making it “difficult to attribute such an analgesic effect to placebo effect alone, which was still effective even after 6 months,” they wrote.

Ultimately, more randomized controlled trials are needed to confirm the findings as well assess whether LLLT affects acute pain intensity and rash severity, among other factors.

The authors reported no disclosures.

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Chen Y, Wang H, Wang T, Li Y, Chen T. Early application of low-level laser may reduce the incidence of postherpetic neuralgia (PHN). J Am Acad Dermatol.2016;75(3):572-577. doi:10.1016/j.jaad.2016.03.050.

This article originally appeared on Neurology Advisor