Sebaceous adenitis is an uncommon dermatosis characterised by alopecia and scaling. It can be idiopathic or associated with other diseases such as leishmaniosis. The condition can occur in any breed, but a breed predisposition has been reported in Standard Poodles, Akitas, Samoyeds, Chow Chows, English Springer Spaniels and Vizslas. An autosomal recessive mode of inheritance has been proposed in Standard Poodles and Akitas. There is no sex predilection and mostly young to middle-aged dogs are affected. Sebaceous adenitis has also been reported in cats and rabbits, but rarely.
Pathogenesis
Destruction of the sebaceous glands results in reduced sebum to coat the hair shaft and the hair follicle infundibulum. This subsequently leads to hyperkeratosis, follicular plugging and weakness in the hair shaft, resulting in fracture and subsequent alopecia.
The mechanism for the destruction of the sebaceous glands is unclear, but T-cell mediated destruction of sebaceous glands, genetic factors and defects in lipid metabolism have all been implicated.
Clinical signs
Generally, the condition is non-pruritic, but with time can become pruritic due to secondary pyoderma. The lesions generally progress from the face and ears (Figure 1) to the trunk. Lesions vary between short-haired and long-haired dogs.
Short-coated dogs generally present with a moth-eaten appearance, due to multifocal annular or serpiginous areas of alopecia and fine scaling.
Long-haired dogs present with poor coat condition with varying degrees of alopecia (localised patches to generalised), follicular casts, adherent scaling on the hair shafts and easily epilated hairs.
Apart from the cutaneous signs, the general health of affected dogs is good.
Diagnosis
Skin scrapes, trichography (Figure 2), fungal culture, haematology, biochemistry and hormonal assays to rule in, or out, other causes of scaling, crusting and alopecia, should be undertaken as appropriate depending on the history and other clinical signs.
The diagnosis of sebaceous adenitis is confirmed on histological findings of:
- Nodular to pyogranulomatous inflammation at the mid-dermis and perifollicular regions
- Inflammatory cell infiltrate composed of histiocytes, lymphocytes, neutrophils and plasma cells
- Small, shrunken, or absent sebaceous glands
- Orthokeratotic hyperkeratosis and irregular hyperplasia
- Follicular hyperkeratosis
Treatment
Several options are available for the management of sebaceous adenitis. Treatment is aimed at improving coat condition, attempting to stop the progression of sebaceous gland destruction and removal of excessive scale.
Topical treatments
Salicylic acid and sulphur-containing shampoos are most useful in the management as they are effective in removing the crusts and scale. Following the shampooing, application of a humectant such as 50 to 70 percent propylene glycol helps moisturise the skin.
Good results have been reported from prewashing with a shampoo containing either sulphur and salicylic acid, or ethyl lactate. A contact time of 10 minutes is allowed before rinsing, after which baby oil is rubbed into the skin, allowed to soak for up to two hours and then rinsed off using the same shampoo. Following this, a humectant is applied.
Systemic treatments
Essential fatty acids
Omega-6 and omega-3 fatty acids combined with topical treatment have been reported to be effective in some dogs. Essential fatty acids help replace fatty acids in hair and skin and they also have anti-inflammatory properties and help maintain the epidermal barrier.
Ciclosporin
Ciclosporin at a dose of 5 to 10mg/kg once daily is a useful treatment in the management of sebaceous adenitis (Figure 3). Adverse effects of ciclosporin include vomiting, diarrhoea, abdominal discomfort, gingival hyperplasia and papillomatosis.
Vitamin A
Vitamin A administered at 10,000 IU orally BID may help some dogs. Dosages up to 20,000 to 30,000 IU can be tried. One study reported an 80 to 90 percent improvement within three months. It is, however, important to note that the clinical signs of vitamin A toxicity include reduced tear production, hepatotoxicity, cheilitis, teratogenicity and xerosis.
Isotretinoin
Isotretinoin, a synthetic retinoid, has been used in the past with some success at dosages of 1 to 3mg/kg SID. This is not licensed for veterinary use and is expensive, and in recent years this medication appears to have been replaced by ciclosporin.
Summary
Idiopathic sebaceous adenitis is a non-curable, but non-life threatening, condition that requires lifelong management. It can affect any breed of dog, but genetic predispositions have been reported. The condition is usually managed with a combination of topical and systemic treatments, depending on individual circumstances.
