Rapid response of hyperkeratotic erythema multiforme to oclacitinib in two dogs.

Background Hyperkeratotic erythema multiforme (HKEM) is a clinically distinct dermatosis and poorly characterized syndrome, comprised of hyperkeratotic plaques with variable symmetry and apoptosis similar to "classic" erosive canine EM. Hyperkeratotic EM has a protracted clinical course and, although treatments with glucocorticoids, azathioprine and/or ciclosporin have been tried, rates of remission are low. Objectives To describe successful treatment of HKEM in two dogs using oclacitinib. Animals A 7-year-old, spayed Havanese dog (Case 1) and a 1-year-old, intact cryptorchid Dachshund dog (Case 2). Methods Case characterization and clinical diagnoses were based on lesion character, surgical biopsy, cytological evaluation, culture, direct immunofluorescence (DIF) and expected responses to treatments. Results Both cases exhibited multifocal, often symmetrical hyperkeratotic plaques with adherent scale. Histological findings revealed prominent epidermal hyperplasia, parakeratotic hyperkeratosis, lymphocytic dermatitis and transepidermal apoptosis with lymphocytic satellitosis. DIF revealed fine, patchy IgG, IgM and IgA basement membrane deposits (Case 2). Both dogs exhibited rapid improvement with oral oclacitinib (0.6-0.9 mg/kg twice daily) with a complete remission of clinical signs observed in 12 and seven weeks in cases 1 and 2, respectively. Conclusion and Clinical Importance Oclacitinib could be considered as a fast-acting and effective treatment option for HKEM in dogs.