Cutaneous Epitheliotropic T-Cell Lymphoma in a Young Shiba Inu Presenting with Persistent Focal Crusting and Severe Mixed Dermatitis: A Case Report

Canine cutaneous epitheliotropic T-cell lymphoma (CETL) may be diagnostically challenging when lesions are clinically subtle and inflammatory in appearance. A 5-year-old spayed female Shiba Inu was evaluated for two approximately 1-cm areas of persistent focal crusting with delayed regrowth of previously clipped hair. The lesions failed to improve despite culture-guided antimicrobial treatment. Histopathology of punch biopsies revealed multifocal infiltrates of intermediate-to-large round cells with mild-to-moderate anisocytosis and anisokaryosis, accompanied by severe mixed dermatitis. Multifocal epidermal and adnexal epitheliotropism was present, and immunohistochemistry demonstrated CD3-positive lymphocytes within epithelial structures. Oclacitinib (0.6 mg/kg twice daily) was initiated but discontinued after 15 days because of haematuria of undetermined cause. Nine days later, multiple new crusted lesions developed. Because clinicopathological uncertainty remained, one of the lesions was sampled for PCR for antigen receptor rearrangement (PARR), which demonstrated T-cell clonality without B-cell clonality. After oclacitinib was reintroduced, no further lesions developed during five months of follow-up. This case underscores that persistent or recurrent crusting unresponsive to initial therapy should prompt biopsy, as apparent improvement with immunomodulatory treatment does not exclude neoplasia and may delay diagnosis and management. However, the short follow-up period of five months limits the assessment of long-term treatment outcomes and prognosis.