Clinical presentation

There seem to be two forms of sebaceous adenitis. In the focal form, there are localized areas of alopecia, erythema, and excessive scaling (the scale is charac­teristically very adherent to hairs). The head and extremities appear to be more consistently involved. Inflammation and pruritus are variable but may be present, especially with a superficial pyoderma. This form is more common in short-coated breeds (e.g., Viszla), and often starts with head or facial involvement and progresses caudally.

A generalized form presents with dramatic amounts of scale on the skin, scale ad­herent to hairs (follicular casting) and the coat and skin often dry to the touch. As the disease progresses (often caudally from the face or head), there is a generalized thinning of the coat. The dorsal back, medial aspect of the pinnae and the ear canals usually are the most affected. Pruritus is vari­able but may be marked, especially if a secondary bacterial pyoderma present. Breeds that are pre­disposed to this form include the Standard Poodle, Samoyed, Akita, Old English Sheepdog, and the Lhasa Apso.

In the past, these problems (especially the generalized form) were likely diag­no­sed as idiopathic seborrheas or endocrinopathy.­

Etiology

An inflammatory process appears to be responsible for destroying the sebaceous glands in the affected areas. The cause for initiation of the inflammatory process is unknown at present. Marked orthokeratotic hyperkeratosis is also noted. This derangement in keratinization may at least in part be a product of the lack of sebaceous glands and their secretions. These patients appear to be prone to the development of secondary bacterial infections, which may contribute significantly to pruritus and hair loss.

Differential diagnoses

For the focal form, differentials are: Infestations (Demodex), infections (bacterial, dermatophyte, Malassezia), zinc-responsive dermatosis, pemphigus foliaceus; for the generalized form: endocrinopathy, idiopathic seborrhea, Leishmaniasis.

Diagnosis

Biopsy of the skin is usually diagnostic. Affected areas show a pyogranulomatous inflam­mation (with neutrophils and macrophages) around the sebaceous glands. Seba­ceous glands are in various stages of being destroyed. Marked ortho­keratotic hyperkeratosis is present (thickening of stratum corneum). In late stage disease, the inflammation resolves, leaving an absence of sebaceous glands.

Treatment

A number of regimens have been used and the response has been variable. Listed below are the regimens used by this author, with preference given to the ones listed first. Treatments may be used in combination, with the exception of using the vitamin A with retinoids (because they are essentially the same type of medication). Treatment of secondary pyoderma is a necessity.

 Vitamin A, oral: small to medium dogs 10,000 IU q12h; large breeds (Akitas, Standard Poodles) 20,000 IU q12h.

 Fatty acid supplementation (double strength); evening primrose oil, 500 mg twice daily.

 Two hour application of bath oil, followed by five to seven shampoos. Repeat twice monthly. Hair loss is seen initially followed by hair regrowth.

 50%–100% propylene glycol sprays applied once daily followed by anti­seborrheic shampoos every three to four days initially. Slowly reduce the frequency of sham­poos initially, and then the frequency of the propylene glycol sprays to the least frequent application that helps to control the problem.

 Isotretinoin (Accutane^®) or acitretin (Soriatane^®) 1–3 mg/kg every 12 hours until remission; then the lowest, most infrequent dose required to control clinical signs.

Other species

Sebaceous adenitis has been reported in cats and rabbits. Treatment protocols are not well established.

References

1.  Rosser EJ, Jr. Sebaceous Adenitis, in Kirk and Bonagura (eds), Current Veterinary Therapy XI, 1992 pp 534-536.

2.  White SD, Rosychuk RAW, Scott KV, et al. Sebaceous adenitis in dogs and results of treatment with isotretinoin and etretinate : 30 cases (1990-1994). J Am Vet Med Assoc, 297: 197-200, 1995.

3.  White SD, Linder, K, Shultheiss P et. al. Sebaceous adenitis in four domestic rabbits (Oryctolagus cuniculus). Vet Dermatol; 11: 53-61, 2000.