Abstract

A 47-year-old man presented to the emergency department for evaluation of rectal pain, night sweats and discomfort. On physical examination, the patient had scattered erythematous papules and plaques on the trunk, groin and perianal skin, each with a central hemorrhagic vesicle. Strikingly, the left inguinal fold had massive lymphadenopathy with a hemorrhagic patch. Punch biopsies were performed of the right upper back and left groin. The specimen from the hemorrhagic groin patch demonstrated subtle interface dermatitis with superficial and deep perivascular lymphocytic and neutrophilic inflammation focused on hair follicles and sweat glands. In contrast, the specimen from a vesicle on the back showed focal full-thickness epidermal necrosis with apoptotic keratinocytes and marked superficial and deep perivascular inflammation and eccrine syringometaplasia. Interestingly, the lymphocytes in the infiltrate were distinctly atypical, with large hyperchromatic, angulated nuclei. No viral inclusions were observed on standard light microscopy, but DNA-based polymerase chain reaction for monkeypox (Labcorp) from a swab of a pustule detected the virus. Additionally, we demonstrated abundant monkeypox virus RNA by in situ hybridization, mainly localized in the epidermis and superficial dermis. Electron microscopy detected abnormal structures resembling mature and immature monkeypox virion, localized within the cytoplasm of keratinocytes of the epidermis and eccrine ductal cells. Monkeypox is an emerging zoonotic disease currently causing a worldwide outbreak and dermatopathologists will need to recognize the histopathological spectrum of this potentially life-threatening infection, even in the absence of frank viral inclusions on light microscopy.

Financial Disclosure:
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