RELATIONSHIP BETWEEN TIME OF TREATMENT OF ACUTE HERPES-ZOSTER WITH SYMPATHETIC BLOCKADE AND PREVENTION OF POSTHERPETIC NEURALGIA - CLINICALSUPPORT FOR A NEW THEORY OF THE MECHANISM BY WHICH SYMPATHETIC BLOCKADE PROVIDES THERAPEUTIC BENEFIT

Background and Objectives. Since Rosenak's original report more than 5 0 years ago as to the efficacy of sympathetic blocks in terminating ac ute herpes zoster, many investigators have reported that a more import ant benefit of this form of therapy is the prevention of post-herpetic neuralgia. However, most of these reports have indicated that sympath etic blocks are effective in preventing post-herpetic neuralgia only i f applied soon after the onset of the acute phase of the disease; in f act, if applied too late, this form of therapy failed to prevent the d evelopment of post-herpetic neuralgia. The present study was carried o ut to determine more precisely the relationship between the time of tr eatment of acute herpes zoster and the prevention of post-herpetic neu ralgia and to attempt to correlate this time with the authors' previou sly published theory on the mechanism by which sympathetic blocks prov ide the therapeutic benefit. Methods. The present study was a retrospe ctive review of 122 patients treated at variable intervals after the o nset of acute herpes zoster. Data tabulated included the duration of s ymptoms at the time of treatment, the number of sympathetic blocks req uired to provide relief, and the efficacy of the sympathetic blockade in terminating the acute phase of herpes zoster and then preventing th e development of postherpetic neuralgia. Result. According to the data obtained in this retrospective study, sympathetic blocks terminated t he pain of acute herpes zoster and prevented or relieved postherpetic neuralgia in more than 80% of patients treated within 2 months of the onset of the acute phase of the disease, after which time the success rate decreased drastically. Conclusion. Sympathetic blockade applied w ithin the first 2 months after the onset of acute herpes zoster termin ated the acute phase of the disease, probably by restoring intraneural blood flow, thus preventing the death of the large fibers and avoidin g the development of post-herpetic neuralgia. If sympathetic blocks we re to be carried out after 2 months, the damage to the large fibers wo uld be irreversible, and this therapeutic modality would not be able t o prevent the development of post-herpetic neuralgia.