MRI diagnosis of muscle denervation from herpes zoster with discordant distribution of the skin rash.

Herpes zoster is a common disorder characterized by a painful rash along a dermatome caused by reactivation of the varicella zoster virus (VZV). Muscle denervation injury from motor involvement is an uncommon phenomenon. Discordant distribution of the skin rash and motor nerve involvement, presenting as a skin rash in one body part and muscle weakness or pain from nerve involvement in another body part is an even more uncommonly reported finding. We present an unusual case of muscle denervation injury resulting from motor involvement of a peripheral nerve by VZV diagnosed by magnetic resonance imaging with cutaneous manifestations in a different dermatomal distribution. To the best of our knowledge, there has been no similar case reported in the English radiology literature. We suggest that whenever a radiologist notices MRI findings suggesting denervation injury and a cause not readily identified, VZV-related denervation injury should be included in the differential diagnosis, especially in an older immunocompromised patient.