Web Chapter 43 Sebaceous adenitis is an inflammatory disease process directed against the sebaceous glands of the skin and has an unknown cause and pathogenesis (Rosser et al, 1987; Scott, 1986). In standard poodles, the results of pedigree analyses and prospective breeding studies of affected animals suggest that sebaceous adenitis is a heritable, autosomal-recessive skin disease of variable expression (Dunstan and Hargis, 1995), and a similar mode of inheritance has been proposed for Akitas with sebaceous adenitis (Reichler et al, 2001). However, thus far ongoing work by Boursnell and colleagues in the United Kingdom has not identified the genomic region involved in the inheritance of this disease in standard poodles. More recently, this project has been expanded, with collaboration from Dr. Niels Pedersen of the Veterinary Genetics Laboratory at the University of California–Davis; thirty-five affected dogs from the United States and 23 affected dogs from the United Kingdom were examined, with encouraging results (Animal Health Trust website, research on Sebaceous Adenitis). The current theory regarding the alopecia observed in this disease is that the loss of sebaceous glands results in the loss of sebum at the level of the infundibulum. Sebum appears to be required for the subsequent dissolution of the outer root sheath of the growing hair (Gates and Karasek, 1965; Stenn et al, 1999), and this may not be occurring as is observed in mice with the hereditary absence of sebaceous glands. The resultant hair shaft has a less developed cuticle for strength and may simply fracture at the level of the follicular ostia as the hair shaft continues to push outward. This may explain why the various surface lipid therapy treatments are so successful in allowing for the normal regrowth of hair in these dogs, as the hair bulb regions are already predominantly in an anagen phase on histopathologic examination. Sebaceous adenitis occurs primarily in young adult to middle-aged dogs, with no apparent sex predisposition. However, more recent reports have indicated the onset of this disease in older dogs, including those aged 7 to 11 years, and this has been the author’s experience as well more recently with this disease (Linek et al, 2005; Reichler et al, 2001). The disease can be divided into two major forms based on their differences in clinical presentation and histopathologic changes (Rosser, 1992). The first form occurs in long-coated breeds and has been recognized most frequently in the standard poodle, Akita, and Samoyed. Over the past decade the disease has been reported with an increasing frequency and has been diagnosed in several other breeds of dogs including the golden retriever, English springer spaniel, Lhasa apso, Old English sheepdog, miniature poodle (Rosser, 2010); cairn terrier, English pointer, Labrador retriever (Spaterna et al, 2003), and Havanese (Frazer et al, 2010). Another recent study on the incidence of sebaceous adenitis in Swedish dogs included a total of 26 affected breeds (Tevell et al, 2008). This form of the disease is characterized by a dull, brittle haircoat, alopecia, moderate to severe scaling, and the formation of follicular casts. Pruritus and malodor are variable and tend to be mild or absent early in the course of the disease and may become moderate to severe in advanced cases or when a secondary bacterial folliculitis develops. In standard poodles, the lesions most commonly affect the dorsal regions of the body, including the dorsal planum of the nose, top of the head, pinnae, dorsal trunk, and tail. When the disease is progressive, the affected areas develop tightly adherent scales (varying from silver-white to brown, depending on haircoat color), with small tufts of hair matted within the scales. The disease in standard poodles may present in several clinical forms: (1) a subclinical form (detectable only on histopathologic examination of skin biopsy specimens of apparently normal skin); (2) a localized, mild, and self-limiting form; (3) a progressive moderate to severe form; and (4) a cyclic form with periods of spontaneous improvement or worsening independent of any treatment. In Samoyeds, the alopecia, scaling, and follicular casts most commonly affect the entire trunk and pinnae. The disease in the Akita may represent its own variant of sebaceous adenitis in long-coated breeds of dogs, as it differs by the additional presence of greasiness of the skin and haircoat and the frequent presence of papules and pustules. Akitas may also show signs of systemic illness, such as fever, malaise, and weight loss (Power and Ihrke, 1990). However, a more recent study of 23 Akitas reported a progression of the disease similar to that observed in standard poodles, both clinically and histologically, and an absence of any systemic signs (Reichler et al, 2001). Also, 16 of the 23 owners of the affected dogs in this study reported that an illness, glucocorticoid or progestagen treatment, general anesthesia, estrus, molting, neutering, or environmental change preceded the onset of the disease. The second form occurs in short-coated breeds of dogs and has been most frequently recognized in the vizsla. This form of the disease is characterized by “moth-eaten,” annular, or diffuse areas of alopecia and mild scaling, with occasional small firm nodules, affecting the trunk, head, and ears. Dogs usually do not have pruritus, and the development of secondary bacterial folliculitis is rare. Because this form of the disease is quite different from the disease in long-coated breeds of dogs, in both its clinical and its histopathologic features, it is believed that this disease may be more appropriately classified as a granulomatous to pyogranulomatous, nodular, periadnexal, dermal, and pannicular dermatitis than as a subgroup of sebaceous adenitis (Rosser, 2010). The breed affected, historical development of the problem, and physical findings are what first lead the clinician to suspect sebaceous adenitis. The diagnosis is confirmed by the histopathologic examination of several skin biopsy specimens that are representative of the different degrees of lesion severity noted during the physical examination. Sites selected for biopsy should include any apparently normal skin, mildly affected areas, and severely affected areas. The most common histologic finding is a nodular granulomatous to pyogranulomatous inflammatory reaction at the level of the sebaceous glands (Rosser et al, 1987; Dunstan and Hargis, 1995; Gross et al, 2005). In the chronic stages of the disease in long-coated breeds of dogs, there is often a complete absence of sebaceous glands with little or no inflammation, perifollicular fibrosis, and marked follicular and surface hyperkeratosis. This may easily be misinterpreted as being consistent with an underlying endocrine skin disease. For this reason it is suggested that such biopsy samples be submitted to individuals specifically trained in veterinary dermatohistopathology. In contrast, in short-coated breeds of dogs, the periadnexal nodular granulomatous to pyogranulomatous inflammatory reaction is usually present throughout the disease process, extending to all adnexal structures (hair follicle wall and apocrine glands as well as the sebaceous glands), the reticular and deep dermis, and panniculus, with occasional complete obliteration and loss of all adnexal structures.
Therapy for Sebaceous Adenitis
Clinical Features
Diagnosis
