Seborrhea in Dogs
Dr. Rosanna Marsalla
Cytology provides information regarding the secondary skin infections, which are present in the majority of cases at time of presentation. Swabs or tape impressions can be prepared and stained.
Differentiation between primary and secondary seborrhea is an important step in the approach of a case of seborrhea. This comes from the history, the distribution of the lesions and exclusion of concurrent disease.
Dogs should be re-evaluated for scaling and pruritus after resolution of skin infections. If scaling is not present any longer, seborrhea was secondary. At that stage the underlying cause for skin infections should be pursued. This is done by evaluating the level of pruritus (itching). If, on the other hand, scaling is still present, then it should be considered whether this is secondary to pruritus or not. If no pruritus is present then diseases like demodicosis, endocrine, autoimmune disease or diseases of keratinization are possible. A biopsy would be indicated to rule in/out diseases.
Treatment of seborrhea includes treatment of secondary skin infections and of the underlying disease of keratinization. Glucocorticoids should not be used during the time in which the diagnostic evaluation is done as they may affect the ability to control the pyoderma and they interfere with the evaluation of pruritus.
Topical therapy rarely works when used alone. However, it is a very effective adjunct therapy to get faster resolution of a skin problem. In general, bathing should be continued over at least a 10 to 15 minute period for proper hydration of the skin and to allow the active ingredients to work.
Shampoos. Best results are obtained by shampooing frequently to control the dermatosis (skin problem) initially and then decreasing the frequency for maintenance of remission. Topical therapy is not a substitute for managing the dermatosis by establishing a definitive diagnosis as soon as possible.
Humectants and emollients. If the seborrhea is dry, humectants and emollients are indicated. Contact time of 10 to 15 minutes should be allowed to properly hydrate the stratum corneum. If contact time is too short or if baths are given too frequently, the effect will be opposite. The application of bath oil when the skin is still wet will help to hold externally applied water to prolong hydration.
Humectants are agents that work by being incorporated in the stratum corneum and by attracting the water that is in the lower layers of the epidermis. These agents include urea, sodium lactate, lactic acid and propylene glycol and work even if applied in between baths. Lactic acid has hygroscopic activity at low concentration and keratolytic activity at higher concentrations. It has been incorporated into liposomes to ensure a slow release over time and thus a longer residual activity (Microperl Humectant Spray®).
Emollients are agents that soften the skin because they decrease transepidermal water loss. They are usually oils and work if applied after a bath. They fill the spaces between dry flakes with droplets of oil.
Degreasers. If the seborrhea is greasy then degreasers are more appropriate. Keratolytic agents cause cell shedding while keratoplastic agents cause a normalization of the epidermal cell kinetics. Most agents used in veterinary dermatology for the treatment of seborrhea have both properties. These products have to be used quite often in order to be effective (two to three times/week).
Tar is keratolytic, keratoplastic, antipruritic, degreasing and drying. It may be irritating and cause photosensitivity. It may stain a white hair coat. It is indicated for cases of greasy seborrhea (cocker spaniel seborrhea).
Sulfur is keratolytic, keratoplastic (0.5 to 2 percent), antipruritic, antibacterial, antiparasitic and antifungal (2 to 5 percent). It is not a good degreaser.
Salicylic acid is keratolytic, keratoplastic, antipruritic and bacteriostatic. In the veterinary formulations, it is usually in the same percentage of sulfur (0.5 to 2 percent).
Selenium sulfide (Selsun Blue®) is keratolytic, keratoplastic, degreasing and effective against yeasts (Malassezia). It can be irritating and drying.
Benzoyl peroxide (2.5 to 3 percent Benzoyl Plus®, OxyDex®, Pyoben®) is keratolytic, antimicrobial, degreasing and very useful in severe cases of greasy seborrhea. It reduces sebaceous glands secretions and has a flushing activity on the bacteria in the hair follicles. Human products should not be used because of irritation (10 percent).
Clipping. A thick hair coat, like the one of a cocker spaniel, will prevent the shampoo from reaching the skin, therefore it is crucial to the success of therapy that the hair is always kept very short. This will reduce the amount of shampoo, will allow better contact with the skin surface and thus enhance efficacy.
Most cases require systemic treatment for secondary skin infections. Antibiotics and antifungal therapy are usually used for three to four weeks.
Systemic therapy for primary diseases of keratinization includes the use of retinoids and Vitamin A derivatives. Retinoids have been tried for the management of this disorder (retinol, isotretinoin, etretinate).
These compounds have the ability to regulate the proliferation and differentiation of epithelial tissues. Isotretinoin seems to work better in cases where the disease is the hair follicle and sebaceous glands (Schnauzer comedo syndrome and sebaceous adenitis), while etretinate works better in hyper proliferative epidermal disorders (idiopathic seborrhea of cocker spaniels, English springer spaniels, Irish setters).
Response to therapy should be seen within the first two months of therapy. Synthetic compounds have a long half-life and are stored for a long time in the body fat.
Toxicity in animals seems to be less of a problem than in humans; however, keratoconjunctivitis secca (dry eye), increase of triglycerides, cholesterol, liver enzymes, pruritus, vomiting, diarrhea and stiffness have been reported. All these compounds are to be avoided in pregnant animals due to potential fetal malformations.