Urticaria pigmentosa

A 14-month-old castrated male domestic shorthair cat presented with an 8 month history of severe pruritus, alopecia, papules and excoriations. Initial evaluation and treatment prior to referral included skin scrape, cytology, two strict food trials, dermatophyte culture, and bacterial culture and sensitivity, as well as antibiotic therapy, empiric treatment for mites, steroids and ciclosporin A (Atopica; Elanco). The cat was referred to the Dermatology and Otology Clinic at the University of Illinois Veterinary Teaching Hospital for further diagnostics and treatment. Skin scrapes were unremarkable. Cytology showed rare bacteria and moderate neutrophils. The cat was given an injection of triamcinolone acetonide, which was ineffective. Oclacitinib (Apoquel; Zoetis) was given for 4 weeks with no improvement. A skin biopsy was performed, and histopathology showed large numbers of well-differentiated monomorphic mast cells with fewer eosinophils that diffusely infiltrated the superficial dermis, supportive of urticaria pigmentosa. Oral dexamethasone and cetirizine hydrochloride were initiated, and the cat responded favorably. At the time of writing, the cat continues to do well on cetirizine hydrochloride with only intermittent tapering courses of dexamethasone. To the best of our knowledge, this is the first reported case of urticaria pigmentosa in a domestic shorthair cat. This case also highlights the importance of biopsy after a thorough, systematic work-up in a cat with severe, intractable pruritus to reveal an uncommon disease pattern, as well as the efficacy of oral dexamethasone and cetirizine hydrochloride as a potential management option