Dermatitis associated with the use of primidone in a dog.

A 9-year-old female dog with progressive pruritic dermatitis was examined 9 months after primidone treatment had been initiated. Alopecia, scaling, ulceration, pigmentation, and fissuring were evident over the dorsal trunk, head, perineum, caudal aspect of the thighs, hocks, elbows, and paws. Hydropic degeneration of epidermal basal cells, mononuclear lichenoid infiltrate in the superficial dermis, and marked parakeratotic hyperkeratosis were evident on biopsy. Antinuclear antibody in the serum was not detected and specific patterns of immunoglobulin deposition in the epidermis or basement membrane zone were lacking. Primidone-induced dermatitis was presumptively diagnosed. Successful treatment involved withdrawal of the primidone and administration of corticosteroids and antibiotics to relieve the pruritus and to eliminate the secondary pyoderma.