Granulomatous sebaceous adenitis

Granulomatous sebaceous adenitis is an uncommon dermatosis in dogs and very rare in cats.

The origin of this peculiar skin disease is still poorly defined. The strong racial predisposition of the Akita Inu and the Poodle suggests a genetic defect in these breeds. The fact that two healthy parents can give birth to some affected puppies and others not, pleads for an autosomal recessive genetic transmission.

In addition to the two leading breeds, there are other breeds at risk: the Samoyede, the Vizla (Hungarian Pointer), the Dachshund and, more anecdotally, the Shih Tzu, the Bobtail, the German and Belgian Shepherds .... No breed seems to be totally spared....

Etiopathogeny (= factors leading to the disease): several hypotheses are still being considered:

• an immunological, cell-mediated attack on the sebaceous glands leading to their destruction (the most likely cause)
• a defect in keratinisation producing inflammation and atropy of the ducts and sebaceous glands
• an anatomical defect of the sebaceous glands leading to a leakage of lipids into the dermis. These lipids would be considered as foreign bodies in the dermis. They would induce a local inflammatory reaction
• a defect in lipid metabolism producing a cornification anomaly and a destruction of the sebaceous glands

The clinical signs differ according to the breed affected and its coat type (Akita Inu, Vizla, Poodle), but also according to the severity and duration of the disease

In granulomatous sebaceous adenitis, the sebaceous glands are altered and the production of sebum is reduced, resulting in the presence of sometimes thick scales and follicular mantles (the hairs seem to be agglomerated, stuck together by a sort of crust starting from the origin of the hairs on the skin surface).

The lesions are often symmetrical. They mainly affect the dorsal part of the trunk, the face, the temples and the auricles. Involvement of the whole body is also possible.

The lesions take the form of :

• Poor coat quality: dry, fine, brittle hair...
• Squames adhering to the skin forming mantles around the hair (follicular mantles)
• Rat tail: lack of hair on the tail and scales sticking together the remaining hair
• Ring-shaped patches with alopecia and scales adhering to the skin (short-haired breeds)
• Bacterial infection (pyoderma) often accompanies sebaceous adenitis (especially Akita Inu)

The diagnosis is based on :

• Clinical appearance of the skin
• Skin biopsy allowing analysis of the skin structures. It shows hyperkeratosis (excessive horny layer), inflammation targeted on the sebaceous glands or atrophy, sometimes with total disappearance of the latter.

Treatment

A study published in the journal Veterinary Dermatology in 2010 shows that the best results in treating this skin disease are obtained by combining local and systemic (oral) treatments. These treatments should be evaluated on the basis of their results, cost and ease of use.

• Shampoos acting mainly on scales and follicular mantles
• Oil baths
• Moisturisers
• Immunomodulators (ciclosporin)
• Quality diet rich in essential fatty acids (EFA) or EFA supplementation
• (Vitamin A)

Conclusion:

Granulomatous sebaceous adenitis is an uncommon disease producing a very poor coat quality in affected individuals. This entity is often better managed when the diagnosis is made early and the proposed local and general treatments are rapidly initiated.

© Luc Beco