Histopathology of peripheral nerves in cutaneous herpesvirus infection

Cutaneous herpesvirus infection is a common viral disorder manifest by epidermal and/or mucosal vesicle formation. Though it is believed that the virus most likely resides in regional sensory ganglia following primary infection and that cutaneous involvement represents reactivation of a latent infection, the histopathology of cutaneous nerves in sites of disease has not been well characterized. In order to assess and characterize the pathologic changes of these nerves, we retrospectively examined 54 cases of cutaneous and mucosal herpesvirus infection as defined by the presence of diagnostic multinucleate epithelial giant cells that demonstrated viral cytopathic effect. Dermal nerves were evaluable in 48 of 54 cases. All cases showed perineural inflammation that consisted of a dense mixed lymphocyte-polymorphonuclear cell infiltrate. Twenty-six cases exhibited intraneural infiltrations accompanied by Schwann cell hypertrophy with nuclear eosinophilia and pyknosis. Frank neuronal necrosis was present in 21 cases, with viral cytopathic effect evident within neurons of four cases. The degree of peri- and intraneural inflammation correlated with the severity of the inflammatory response within the dermis in most cases; however, in eight cases there was inflammatory involvement of neurovascular structures distant from and out of proportion to dermal and epidermal changes. Immunoperoxidase staining using a polyvalent antibody to human herpesvirus was performed in two cases and demonstrated viral antigen within nerve twigs. This pattern of peripheral nerve twig inflammation, along with the occurrence of more distant neural involvement, may prove to have diagnostic implications and serve as a clue in the recognition of cutaneous herpesvirus infection, particularly in cases with subtle or absent epidermal alteration. Furthermore, the presence of inflammation within and around nerves as well as degenerative changes suggest that nerve twigs are not passive conduits for viral spread but may be directly involved in infection.