LLLT, also known as photo biomodulation therapy, involves the use of low-power lasers or light-emitting diodes to alter cellular function. It is used to reduce inflammation, enhance tissue repair, and modulate pain perception.

Post herpetic neuralgia (PHN) is a persistent neuropathic pain condition that can occur after an episode of herpes zoster (HZ), commonly known as shingles (Painful Rash). HZ is caused by the reactivation of the varicella-zoster virus (VZV). After the initial infection, the virus remains dormant in nerve cells. Factors like aging or immunocompromised states can lead to its reactivation, resulting in HZ.

PHN is characterized by prolonged pain and abnormal sensations that persist for 120 days or more after the initial HZ rash. Pathophysiology of PHN involves damage to both peripheral and central nerve systems. This damage leads to spontaneous nerve firing and increased sensitivity to stimuli, contributing to the chronic pain experienced by PHN patients. HZ typically manifests as a painful rash localized to one dermatome (area of skin supplied by a single nerve root). The rash progresses from erythematous maculopapular lesions to vesicles, pustules, and eventually scabs. PHN manifests as ongoing pain and discomfort in the affected area long after the rash has resolved. PHN significantly impacts quality of life due to chronic pain. It can lead to exhaustion, depression, sleep disturbances, appetite loss, weight loss, and cognitive decline in some cases 1, 2.

Treatment strategies for PHN include prevention through vaccination, prompt treatment of acute HZ to reduce the likelihood of PHN, and multimodal approaches involving drugs and interventions to manage PHN symptoms effectively 1, 2, 3.

LLLT is a therapeutic approach used for inflammation and pain reduction, functional restoration, and stimulation of healing. It works by triggering various cellular responses in the skin, such as improved blood circulation, release of nitric oxide, increased ATP production, and activation of stem cells for tissue repair. Beyond pain relief, LLLT has been shown to improve functional outcomes in PHN patients. This includes improvements in range of motion, sensory function, and overall quality of life. Studies are being conducted to evaluate its effectiveness in alleviating PHN symptoms. PHN is a challenging condition characterized by persistent pain following an episode of HZ. Understanding its pathophysiology and employing effective treatment strategies, including emerging therapies like LLLT, are crucial for improving outcomes and quality of life for affected individuals 4.

The Cochrane risk of bias approach was applied for qualitative assessment in the articles that were selected for the purpose of investigation (Figure 2). Some of the strategies used to evaluate bias included creating a random sequence, selective reporting, concealing the allocation, additional sources of bias such as inadequate outcome of data, blinding staff and participants, and blinding outcome evaluation. The reviewer's assessments of High, Low, and Unclear risk of bias are assessed based on each specific article selected for the study by researcher (author 5) (Figure 3).

We pooled the continuous VAS data from each trial to generate a standardized mean difference (SMD) with a 95% confidence interval (CI) using a random-effects model. The heterogeneity between the studies was investigated using the I-squared statistical test, ranging from 0% to 100% and with a P value less than 0.05 as significant. Using RevMan software, a forest plot was generated to produce the quantitative analysis (Figure 4) by the researcher (Author 1).

While the exact physiological pathways of LLLT in treating PHN remain unclear, studies suggest that it may increase local blood flow and induce analgesia through mechanisms such as vasodilation and modulation of pain-modulating chemicals. This increased blood flow, observed through laser Doppler blood flow measurements, correlates with improved clinical outcomes in PHN patients. Numerous studies, including those by Moore et al., 9 and Kemmotsu et al., 8 have demonstrated the effectiveness of LLLT in reducing pain and improving symptoms associated with PHN. For instance, the use of an 830 nm diode laser and GaAlAs diode laser showed significant pain reduction and improvement in neuropathic pain scores (NPS) and Visual Analog Scale (VAS) ratings 10. Clinical trials and pilot studies have consistently reported substantial pain relief and symptom improvement in PHN patients treated with LLLT. Responses have been positive in both acute and chronic stages of PHN, with some studies indicating LLLT's potential to reduce the incidence of PHN when applied early (within five days of Herpes zoster outbreak) 11, 12, 13. Individual case studies, such as the 15-year-old case mentioned, illustrate dramatic reductions in pain scores and resolution of symptoms following LLLT treatment. These cases underscore the potential for LLLT to provide long-lasting relief and improve quality of life in patients resistant to other treatments. The promising results from these studies suggest that LLLT could play a significant role in managing PHN, potentially reducing reliance on analgesic medications, and improving outcomes for patients, including those with unique circumstances such as PHN in COVID-19 patients 14, 15, 16, 17, 18, 19, 20, 21, 22. In conclusion, while further research is needed to fully elucidate the mechanisms and optimize protocols for LLLT in PHN treatment, current evidence strongly supports its efficacy and safety as a therapeutic option. LLLT offers a non-invasive, well-tolerated approach that may provide substantial pain relief for PHN patients, representing a valuable addition to the treatment armamentarium for this challenging condition.

While studies have demonstrated the efficacy of LLLT in reducing pain intensity and improving symptoms in PHN patients, there remains a need to systematically investigate how these improvements translate into broader aspects of quality of life which encompasses physical, psychological, and social well-being, which are all affected by chronic pain conditions like PHN.

In conclusion, the systematic review and meta-analysis provide robust evidence supporting LLLT as a beneficial and safe treatment option for reducing pain in patients with post-herpetic neuralgia. Due to the limited number of studies and variations in study design and intervention application, the study offers a high level of heterogeneity. The absence of reported adverse effects underscores its potential as a well-tolerated therapeutic approach. Therefore, it is recommended for clinicians and policymakers considering and integrating LLLT as a first-line treatment for PHN. Continued research and clinical application of LLLT will further elucidate its role in optimizing outcomes and improving quality of life for individuals living with PHN.