Long-Term Effects of Spinal Cord Stimulation on Pain in Postherpetic Neuralgia.

Introduction: Postherpetic neuralgia (PHN) is a pain syndrome that develops within few months after the acute herpetic outbreak. The pain may be accompanied by specific cutaneous signs in the distribution of affected dermatomes and feel unbearable reaching up to 9-10/10 on visual analog scale (VAS). Despite the introduction of new medications, drug resistance develops in at least 50% of cases. Neuromodulation techniques such as spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS) are considered as ones of the last resorts for PHN treatment, especially in pharmacoresistant patients. Recently, several studies with limited number of cases have shown high efficiency of neuromodulation (regression of pain syndrome in more than 82% of cases) after SCS in PHN patients, but these findings require further confirmation and have not been supported by large RCTs.

Methods: Initially, 32 patients diagnosed with chronic drug-resistant PHN underwent a trial of SCS. Based on the trial results, a decision was made whether to implant a permanent SCS system. The condition of all patients implanted with SCS system was assessed using the VAS, SF-36, Patient Global Impression of Change (PGIC), and Medicine Quantification Scale, version III (MQS) questionnaires before the surgery and in the long-term follow-up. We also conducted systematic follow-up of patients who did not pass the test stimulation stage, using them as a control group to track the levels of pain. The hypothesis of normal distribution for quantitative values was tested using Shapiro-Wilk tests.

Results: During the trial period, tonic spinal stimulation was effective in 16 out of 32 (50%) patients with drug-resistant PHN. Among 14 patients with implanted stimulators, a significant pain reduction (more than 50% from the baseline) was observed in 10 patients (71.4%). The pain level in patients with a tonic SCS was statistically lower than in patients receiving conservative therapy. For the entire group of patients with implanted SCS, a significant improvement was also observed in results of SF-36, PGIC, and MQS.

Conclusion: Our clinical series demonstrates that tonic SCS was effective in 50% of patients with refractory PHN undergoing SCS trial. Significant improvement in pain control obtained during the long-term follow-up in patients treated with tonic SCS improves the quality of life and reduces the need for analgesic medications.