13 Sebaceous adenitis
Sebaceous adenitis is a scaling, variably pruritic skin disorder of uncertain aetiology. The disease results in the inflammation and destruction of sebaceous glands, follicular hyperkeratosis and commonly, secondary pyoderma. Grossly, the disease results in a scaling skin disorder associated with follicular cast formation and variable alopecia.
There are marked breed variations in the way sebaceous adenitis presents, but typically the owner will report a gradual onset of skin lesions with variable scaling, alopecia and pruritus. The head and pinnae are often the first areas to be affected. The earlier signs of the disease may go relatively unnoticed and the dog may be presented with more severe lesions due to secondary pyoderma. There are no systemic signs associated with the disease.
Longer-haired dogs present with variable scaling, alopecia and usually marked follicular cast formation (Fig. 12.4), and a fine silvery scale on the inner aspects of the pinnae is commonly seen in springer spaniels. Lesions can progress to large patches of broken hairs and tightly adherent scale. The pinnae, trunk, temporal region and tail tend to be affected in the early stages, but severe disease can result in generalized involvement.
Feline sebaceous adenitis is a rare disease characterized by multifocal annular areas of alopecia, scaling, crusting and follicular casts. Pruritus can be absent to marked, and tends to be more severe if there is secondary pyoderma.
This was a diffuse, partial alopecia involving scaling and follicular cast formation. Follicular casts are made up of keratosebaceous material, and are literally a cast of the hair follicle lumen that forms a collar around the hair shaft and is extruded from the hair follicle as the hair grows (see Chapter 12). They represent follicular pathology, in particular follicular hyperkeratosis.