1. General Considerations

   1. In primary seborrhea, an underlying cause cannot be identified.
   2. Primary seborrhea is an uncommon keratinization disorder.
   3. Seborrhea is rare in cats. Breeds affected include Persian, Himalayan and exotic shorthaired cats.
   4. Many canine breeds have been reported to be at risk to develop primary seborrhea including the American cocker spaniel, English springer spaniel, West Highland white terrier, Irish setter, basset hound, dachshund, Doberman pinscher, German shepherd dog, Chinese shar pei, and Labrador retriever.
   5. Primary seborrhea has been shown to have an autosomal recessive trait in West Highland white terriers and in Persian cats.

2. Pathogenesis

   1. The pathogenesis of primary seborrhea is not completely understood.
   2. Studies in cocker spaniels with seborrhea have demonstrated hyperproliferative changes in the epidermis, hair follicle infundibulum, and sebaceous glands when compared to normal dogs.
   3. The epidermal cell renewal time in seborrheic cocker spaniel dogs has been shown to be approximately 62% faster compared to healthy cocker spaniels (8 days versus 21 days). Similar results have also been reported in Irish setters with seborrhea.
   4. A primary cellular defect is suspected because the hyperproliferative changes of seborrheic skin persist when grafted onto the skin of normal dogs.

3. Clinical Signs

   1. The onset of signs in dogs is usually before 2 years of age and within the first 6 weeks of life in cats.
   2. Depending on the dog breed, clinical signs may range anywhere from dry scaling (i.e. seborrhea sicca) to greasy scaling (i.e. seborrhea oleosa) to scaling and greasiness with inflammation and pruritus (i.e. seborrheic dermatitis) or to any combination of these clinical abnormalities.
   3. Seborrhea sicca:
      1. It is characterized by focal to diffuse accumulations of a dry, non-adhered white to gray scales.

1. 1. 2. The hair coat is usually dull and dry.
      3. Breeds predisposed to seborrhea sicca include Doberman pinchers, Irish setters, German shepherd dogs, and dachshunds.
   4. Seborrhea oleosa:
      1. It is characterized by a generalized, malodorous, greasy skin and hair coat.
      2. There are accumulations of brownish-yellow, greasy material that adheres to the hair (casting) and skin surface.

1. 1. 3. Intertriginous areas, neck, and feet (ventral aspect and interdigital) are the most severely affected regions.
      4. Frequently, there is a concurrent ceruminous otitis and hyperplastic otitis.
      5. Breeds predisposed to seborrhea oleosa include Basset hound, American cocker spaniel, English springer spaniel, Labrador retriever, shar-pei, and West Highland white terrier.
   5. Seborrheic dermatitis:
      1. It is characterized by generalized, malodorous, greasy skin and hair coat (i.e. seborrhea oleosa), along with moderate to severe generalized inflammation, pruritus, and inflamed hyperkeratotic patches.
      2. Secondary bacterial folliculitis and Malassezia and/or bacterial overgrowth are commonly present in seborrhea oleosa cases and will aggravate the primary condition.
      3. Commonly involved areas are the external ear canals, pinnae, ventral neck, chest, intertriginous regions, and perineum.
      4. This presentation of primary seborrhea appears to be a more severe variant of seborrhea oleosa since it is generally seen in the same breeds.
   6. In cats, clinical signs are variable and usually start within the first 6 weeks of life. Severe seborrhea in kittens 2 to 3 days old is characterized by excessive waxy material pasting together groups of hair shafts giving the cat a dirty appearance. Over time, the affected cats develop generalized scaling, alopecia, and oily skin. Ceruminous debris accumulates in facial folds and ears. Cats often have a rancid malodor. In milder cases, the early signs are not apparent until 6 weeks of age.

4. Diagnosis

   1. A definitive diagnosis of primary seborrhea requires a number of supporting factors including age of onset, breed, history, and more importantly, elimination of the various underlying disorders that can trigger an abnormal keratinization process. Skin biopsy can support the presumptive clinical diagnosis and help rule out the diseases in the list of differential diagnoses.
   2. The most important aspect of the diagnostic plan is a thorough investigation to search for an underlying disease or triggering cause.
   3. The primary differential diagnoses are allergic dermatitis, scabies, dermatophytosis, demodicosis, lice infestation, cheyletiellosis, bacterial folliculitis, hypothyroidism, ichthyosis, vitamin A responsive dermatosis, and nutritional deficiencies.

5. Treatment

   Dogs:

   1. Before considering a  seborrhea case as primary or idiopathic, it is important to look for an underlying disease that can be causing the seborrhea.
   2. Because in primary seborrhea an underlying disease or triggering cause cannot be identified, the primary goal should not be to cure the disease but to control the abnormal epidermal keratinization as well as possible.
   3. Topical therapy is always indicated in primary seborrhea.
   4. The specific type and frequency of topical therapy will vary with the severity of clinical signs.
   5. Mild seborrhea sicca cases will respond to frequent applications of moisturizers shampoos and rinses containing one or more of the following ingredients: propylene glycol, glycerin, colloidal oatmeal, urea, sodium lactate, carboxylic acid, and lactic acid.
   6. Keratolytic and keratoplastic shampoos containing sulfur and salicylic acid may be needed to remove heavier dry scales.
   7. Stronger keratolytic, keratoplastic, and degreasing agents (e.g. benzoyl peroxide, tar, sulfur, and selenium sulfide) are needed to control the greasy scales, crusts, and odor associated with seborrhea oleosa.
   8. Moisturizing rinses are often recommended after shampooing.
   9. Initially, shampoos and rinses may be used two to three times a week until the excessive scaling is controlled. Then, a maintenance-bathing program is continued as needed, often at least weekly.
   10. Topical therapies containing ceramides, phytosphingosine, ophytrium, seboliance, and essential fatty acids, with potential for restoring the skin barrier may be used as adjunctive therapy.
   11. Ceruminolytic ear flushes may be used in cases of ceruminous otitis externa.
   12. Seborrhea sicca may respond partially to systemic essential fatty acids.
   13. Vitamin A (retinol) at 10,000 IU can be given orally and once daily with a fatty meal. The effect, if any, may take as long as 8-10 weeks to be noted. The dose based on body weight (1,200 IU/kg) has shown to be safe. Potential side effects such as, keratoconjunctivitis sicca, liver toxicity etc. can occur during treatment; therefore, the patient has to be closely monitored.
   14. A synthetic retinoid named etretinate has been an effective therapy for some cases of primary seborrhea, especially, in American cocker spaniels. The recommended dose is 1 mg/kg orally every 24 hours.
       1. Response to etretinate may take as long as 2 months. Maintenance alternate-day therapy may be required for the life of the animal. It is important to monitor closely for potential side effects associated with synthetic retinoids (e.g. keratoconjunctivitis sicca and liver toxicity).
       2. This treatment option should be reserved for severe cases refractory to other treatment modalities.
   15. Bacterial infection and/or Malassezia and bacterial overgrowth can complicate cases of primary seborrhea and should be identified and treated properly.

Cats:

1. 1. As for dogs, the treatment is symptomatic.
   2. No effective treatment has been reported for severely affected cats.
   3. The condition may be controlled in mildly affected cats with frequent grooming and baths with antiseborrheic shampoos.
   4. The hair coat should be kept short.

References

Kwochka KW: Primary Keratinization Disorders of Dogs.  In: Griffin CE, Kwochka KW, MacDonald JM (eds).  Current Veterinary Dermatology.  St Louis, Mosby Year Book, 1993; p 176-190.

Kwochka KW: Overview of normal keratinization and cutaneous scaling disorders of dogs.  In: Griffin CE, Kwochka KW, MacDonald JM (eds).  Current Veterinary Dermatology.  St Louis, Mosby Year Book, 1993; p 167-175.

Miller, Griffin and Campbell.  Chapter 14. Keratinization defects. In: Muller & Kirk’s Small Animal Dermatology. 7th ed., W.B. Saunders, Missouri, 2013; p 630-646.

Power HT, Ihrke PJ.  Synthetic retinoids in veterinary dermatology.  Vet Clin North Am: Small Anim Pract, Philadelphia, WB Saunders, 1990; p 1525.