A case of atypical orf virus infection of the hand in an immunocompromised patient.

Human orf virus infection is a rare zoonotic disease that can clinically and radiologically mimic inflammatory or neoplastic conditions. Typical orf infection presents in immunocompetent individuals as a self-limited cutaneous lesion on the hands or fingers. Typical orf infection evolves through characteristic stages, including a targetoid nodule with central necrosis, white halo, and peripheral erythema, and usually resolves spontaneously within 4-8 weeks. In contrast, atypical orf infection occurs predominantly in immunocompromised patients and is characterized by giant, persistent, or disseminated tumor-like lesions with a prolonged and often recurrent course. In this case report, we present the imaging and histopathological findings of confirmed orf virus infection, illustrating the close correlation between radiologic features and the underlying pathology. We describe the clinical course of atypical orf viral infection presenting as an enlarging exophytic digital mass of the hand in a post-transplant patient, highlighting the challenges in diagnosis and management of atypical viral infectious lesions in immunocompromised patients, which may mimic the clinical presentation of a malignant tumor. Typical imaging findings include well-circumscribed dermal or subcutaneous nodules with peripheral enhancement and surrounding inflammatory reaction, corresponding histologically to epidermal hyperplasia with eosinophilic intracytoplasmic inclusion bodies. Recognizing this radiology-pathology correlation is essential, as atypical cases may raise concern for bacterial abscess, atypical mycobacterial infection, cutaneous lymphoma, or squamous cell carcinoma. Awareness of these features can help radiologists and pathologists suggest the correct diagnosis and prevent unnecessary procedures.