Postherpetic foot drop in an elderly case: undiagnosed diabetes mellitus?

Postherpetic neuralgia is the most commonly seen complication of herpes zoster, primarily in elderly and immunocompromised patients. However, motor involvement due to herpes zoster is very rare. A 65-year-old male patient presented with left leg pain, numbness and difficulty walking. He was diagnosed with having herpes zoster and treated with valacyclovir. Despite anti-convulsant and physical therapy, the patient developed foot drop and had an unexplained weight loss. Clinical and laboratory findings suggested previously undiagnosed diabetes mellitus. Three weeks after initiation of insulin treatment, he became normoglycemic, his pain was reduced, and foot drop disappeared almost completely. Postherpetic motor involvement as an unusual complication may signal an underlying systemic disease, particularly in elderly.