Granuloma annulare as an isotopic response to herpes zoster.

BACKGROUND: Wolf's isotopic response is the phenomenon of a new skin disease occurring at the site of another unrelated and already healed skin disorder. Most cases in the literature report herpes zoster (HZ) as the original disease; however, the isotopic responses vary greatly. Including this case, our literature search revealed 32 cases of isotopic granuloma annulare (GA) following HZ. CASE REPORT: An 82-year-old male presented with GA localized to the right T9 dermatome that later appeared at other sites on the trunk and extremities. The patient had an episode of shingles involving the same dermatome 4 years earlier. DISCUSSION: To our knowledge, this is the first case report of GA occurring initially as an isotopic response in an HZ scar and subsequently becoming generalized. Thirty-eight percent (12 of 32) of patients with isotopic GA following HZ were immunocompromised, which is similar to the published rate of immunodeficiency in patients with HZ.