Relationship between time of treatment of acute herpes zoster with sympathetic blockade and prevention of post-herpetic neuralgia: clinical support for a new theory of the mechanism by which sympathetic blockade provides therapeutic benefit.

BACKGROUND AND OBJECTIVES: Since Rosenak's original report more than 50 years ago as to the efficacy of sympathetic blocks in terminating acute herpes zoster, many investigators have reported that a more important benefit of this form of therapy is the prevention of post-herpetic neuralgia. However, most of these reports have indicated that sympathetic blocks are effective in preventing post-herpetic neuralgia only if applied soon after the onset of the acute phase of the disease; in fact, if applied too late, this form of therapy failed to prevent the development of post-herpetic neuralgia. The present study was carried out to determine more precisely the relationship between the time of treatment of acute herpes zoster and the prevention of post-herpetic neuralgia and to attempt to correlate this time with the authors' previously published theory on the mechanism by which sympathetic blocks provide the therapeutic benefit.
METHODS: The present study was a retrospective review of 122 patients treated at variable intervals after the onset of acute herpes zoster. Data tabulated included the duration of symptoms at the time of treatment, the number of sympathetic blocks required to provide relief, and the efficacy of the sympathetic blockade in terminating the acute phase of herpes zoster and then preventing the development of post-herpetic neuralgia. RESULT: According to the data obtained in this retrospective study, sympathetic blocks terminated the pain of acute herpes zoster and prevented or relieved post-herpetic 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 within the first 2 months after the onset of acute herpes zoster terminated the acute phase of the disease, probably by restoring intraneural blood flow, thus preventing the death of the large fibers and avoiding the development of post-herpetic neuralgia. If sympathetic blocks were to be carried out after 2 months, the damage to the large fibers would be irreversible, and this therapeutic modality would not be able to prevent the development of post-herpetic neuralgia.