Without any clinical information, I hesitate to make this diagnosis. The dermatologist said this elderly patient presented with a cluster of erythematous slighlty indurated lesions in a unilateral dermatomal distribution on the right flank. He said if there were vesicles, it would be perfect for herpes zoster/shingles. The patient was otherwise healthy. This biopsy had a superficial and mid-dermal granulomatous infiltrate, with multinucleate histiocytes and lymphocytes predominating. Some areas looked granuloma annulare-like, although without increased mucin. Special stains were negative for fungal and acid fast organisms and I did not identify herpes viral cytopathic changes. Focusing on the dermal changes, I almost brushed past the vasculitis in the subcutis, which appears primarily lymphocytic. I did not see any vasculitis in the dermis. Carlson noted one case of lymphocytic vasculitis in a post-herpes infection case, but typically the vasculitis is more often reported to be granulomatous in post-herpes zoster infection. The vessel went away on deeper levels so I couldn’t evaluate it further. I think it’s important to rule out other possible causes of vasculitis and other sources of infection, but I think given the clinical presentation and the histology, this was a nice case of post herpes zoster granulomatous dermatitis with vasculitis.
Cutaneous Vasculitis Update: Neutrophilic Muscular Vessel and Eosinophilic, Granulomatous, and Lymphocytic Vasculitis Syndromes J. Andrew Carlson and Ko-Ron Chen, MD, PhD. Am J Dermatopathol 2007;29:32–43