The early lesions include alopecia (hair loss) with excess scaling and brittle hairs. The top of the head, the dorsal planum of the nose, dorsal neck and dorsal midline are commonly affected areas.
Sebaceous adenitits has a cyclic pattern in some dogs with periods of improvement and worsening. Symptoms are slightly different according to the type of hair coat: In short coated breeds (Vizlas), circular areas of alopecia with fine, white, non-adhering scaling are commonly the first manifestation of the disease. Infections are not common in these dogs and itchiness is usually not present.
In poodles, the scales are tightly adherent and follicular casts – accumulations of keratinous debris around the hair shaft seen protruding from the follicle – are visible.
In Akitas, seborrhea oleosa is usually the first sign. Greasy, yellow follicular casts are common. These animals tend to get systemically ill. Concurrent epilepsy has been reported in some dogs. Secondary bacterial infection is common, causing itchiness.
In Samoyeds the most severe sign is alopecia on the trunk with follicular casts.
Diagnosis of sebaceous adenitis is made by histopathology, and several biopsies may be needed to make a final diagnosis. Biopsies should be taken from affected and non-affected skin. Subtle early lesions are most useful to document active inflammation.
Secondary bacterial infection and Malassezia dermatitis are commonly present at the time of initial evaluation. Cytology is important to determine the type and severity of the infection. Infections should be cleared before skin biopsies are taken to minimize secondary non-specific changes.
Pathological changes of the tissue vary according to the stage of the disease.
At the beginning, a nodular inflammation targeting the sebaceous glands is evident. Discrete nodules of histiocytes, neutrophils and lymphocytes are seen at the site of sebaceous glands. One disease that can appear similar to the inflammatory stage of sebaceous adenitis is the sterile pyogranuloma syndrome. However, in the latter, the inflammation is less focused on the sebaceous glands and clinically it has raised firm nodules rather than with scaling and alopecia.
As the disease progresses, the inflammation decreases until sebaceous glands are no longer evident.
When biopsy samples are submitted, pathologists should be made aware of the suspicion of sebaceous adenitis so that multiple biopsy sections are prepared and special attention is paid to the number and shape of the sebaceous glands.