Sebaceous Adenitis

Sebaceous adenitis is uncommon in dogs and rare in cats. The cause is unknown, but the strong predisposition of certain canine breeds suggests that genetics plays a role. The proposed pathogenesis includes cell-mediated immunologic destruction of the sebaceous gland; a primary cornification disorder of the glandular duct, resulting in obstruction and secondary inflammation of the gland; an anatomic defect of the sebaceous gland, leading to lipid leakage and a foreign body reaction; or an abnormal lipid metabolism, leading to glandular destruction. Predisposed breeds include Standard Poodles, Akitas, Samoyeds, Vizslas, Havanese, Springer Spaniels, and Lhasa Apsos; however, various other breeds can be affected. Lesions typically affect the pinnae, forehead, face, tail, and dorsal trunk and are characterized by alopecia and adherent scales that cast hair shafts. The severity and characteristics of clinical signs vary among breeds. Pruritus is variable and mostly associated with secondary bacterial infection. Histopathologic findings include diffuse absence of sebaceous glands, granulomatous to pyogranulomatous inflammation at the site of previous glands, and follicular keratosis. Currently, the most efficacious therapy for sebaceous adenitis is oral cyclosporine (5 mg/kg/day) in association with topical therapy. Oral vitamin A (1,000 IU/kg/day) or synthetic retinoids (eg, isotretinoin or acitretin) may be efficacious in some cases. The combination of tetracycline (250 mg, tid, for dogs <10 kg; 500 mg, tid, for dogs >10 kg) or doxycycline (5 mg/kg, bid) and niacinamine (250 mg, tid, for dogs <10 kg; 500 mg, tid, for dogs >10 kg) is an option for milder cases or when owners are concerned about costs and/or adverse effects associated with cyclosporine or retinoids. Topical therapy in the form of medicated shampoos and emollient rinses or sprays should be used in conjunction with systemic therapy. Omega-3 and omega-6 fatty acids can also be used as adjunctive therapy. To help soften the adherent scales, a mixture of 70%–75% propylene glycol in water can be sprayed or used as a rinse on the animal’s coat and allowed to act for 2–3 hr before bathing with a medicated shampoo. Another option is to apply baby oil soaks (undiluted or diluted with water 1:1) for 1–6 hr before bathing with a medicated shampoo.