Urticaria Pigmentosa Treated with Antihistamine in a Mixed Cat

A six-month-old, intact female, 1.18 kg mixed-breed cat was referred because of severe pruritus and an erythematous lesion on both ear margins.The referring veterinarian prescribed systemic antibiotic treatments, including Cephalexin at a dosage of 20 mg/kg twice daily for five days, Doxycycline at 5 mg/kg twice daily for two weeks, and Metronidazole at 10 mg/kg twice daily for two weeks, along with oral prednisolone at 0.5 mg/kg twice daily for five days.However, no improvement was observed.Surgical excision of bilateral ear margins did not help with a resolution.The clinical examination revealed a papulocrustous lesion on the ear pinna and a left medial hind limb.The left popliteal lymph node was slightly enlarged.The cytological samples from the skin lesions on the ear margin and left medial hind limb confirmed a secondary bacterial infection.The cytology of the lymph node revealed neutrophilic lymphadenitis.A skin biopsy was performed on both the right ear margin and the left medial hind limb under sedation.The histopathological examination showed moderate perivascular diffuse infiltrate of well-differentiated, non-malignant featured mast cells with neutrophils and eosinophils in the dermis.A definitive diagnosis of urticaria pigmentosa was made based on the clinical signs and histopathological results.The cat was administrated cetirizine (1.7 mg/kg) once daily.Evident improvement was noted after two weeks of treatment.The same treatment was continued for seven days, resulting in complete remission.No relapse occurred after the medication was withdrawn.