Role of impaired glucose metabolism in the postherpetic neuralgia.

Background: Postherpetic neuralgia (PHN) is one of the most common and debilitating sequela of herpes zoster. The etiology of PHN is not completely understood. Several studies showed that diabetes mellitus may increase the risk of infectious diseases, including herpes zoster. Instead, the relationship between PHN and prediabetes has never been described.

Objective: To evaluate glucose metabolism abnormalities in patients with PHN.

Methods: We studied 87 consecutive patients with PHN and normal fasting glycemia and 108 pain-free controls. In both groups we evaluated glucose and insulin levels after a 2-hour oral glucose tolerance test and insulin resistance. In addition, in all patients we performed skin thoracic biopsy to exclude a small fiber neuropathy.

Results: After a 2-hour oral glucose tolerance test, the prevalence of glucose metabolism abnormalities was significantly higher in patients than in controls (P<0.001): impaired glucose tolerance was found in 36 (38%) patients and in 16 (15%) controls, whereas a newly diagnosed diabetes mellitus was found in 9 (9%) patients and in 6 (5%) controls. The insulin resistance showed no significant differences between patients and controls.

Conclusions: Our study suggests that PHN may be a marker for impaired glucose tolerance. A glucose tolerance test should be considered in patients presenting with PHN.