Scaling or keratinization disorders in dogs (Proceedings)
Scaling or keratinization disorders are a common dermatologic condition in dogs. This dermatologic problem can be described in two methods (i.e. clinical signs and etiology). Clinical signs associated with scaling or seborrhea can be described as seborrhea sicca or seborrhea oleosa. Seborrhea sicca is a condition where loose white dry scales are present in the hair coat. The hair coat is also usually dull and dry. Seborrhea oleosa is a condition where greasy, yellow brown scales occur with an oily hair coat. Often times, the keratin deposits are adhered to hairs and the dog have a rancid fat odor. Secondary Malassezia or bacterial infections are common when seborrhea oleosa is present.
Possible etiologies for keratinization disorders in dogs include primary and secondary causes. Examples of primary keratinization disorders include hereditary, idiopathic and nutritional. A long variety of differential diagnoses exist for secondary causes for seborrhea. Each of these differentials will be discussed along with possible treatment options.
Primary keratinization disordersDisorders of primary keratinization can be classified into hereditary, idiopathic and nutritional. Hereditary dermatologic conditions usually initially are noticed around 6 months to 3 years of age. Examples of hereditary keratinization includes: color dilution alopecia, follicular dystrophy, icthyosis, lichenoid psoriasiform dermatosis, sebaceous adenitis, Schnauzer comedo syndrome, epidermal dysplasia and primary idiopathic seborrhea. Examples of idiopathic keratinization disorders include: acne, ear margin seborrhea and nasodigital hyperkeratosis. Nutritional keratinization disorders in dogs are: zinc responsive dermatosis, vitamin A responsive dermatosis and a fatty acid deficiency. The most effective way to diagnose hereditary and nutritional keratinization disorders is with a skin biopsy. Idiopathic keratinization disorders are ruled in or out by clinical findings and lack of a definitive diagnosis on skin biopsies.
Primary keratinization disorders are controllable but not curable. Topical antiseborrhea shampoos, sprays and lotions are useful. Vitamin A can help cases of Vitamin A responsive dermatosis and some cases of icthyosis and sebaceous adenitis. In the past, isotretionoin was used but it has been recalled by the FDA. Instead, some veterinarians have used acitretin at a dose of 1 to 2 mg/kg every 24 hours. Some of the more commonly seen side effects for Systemic vitamin A compounds have been associated with hepatotoxicity, keratoconjunctivitis sicca or dry eye, and GI upset.
Secondary keratinization disorders
Seven different secondary keratinization disorders exist. These disorders include: parasitic, allergic, endocrine, pyoderma, autoimmune, dermatophytosis and neoplasia. Examples of parasitic causes include: Cheyletiella, Demodex, and Sarcoptes. Examples of allergies that cause scaling include atopic dermatitis, food allergies, flea allergies and contact allergies. Hypothyroidism, Cushing disease and sex hormone dermatoses are the differential diagnoses for endocrine induced scaling. Pyoderma or bacterial skin infection with epidermal collarettes can result in scaling as the epidermal collarettes break off and try to heal. Autoimmune skin diseases such as pemphigus foliaceous have also been associated with scaling. Dermatophytosis or fungal skin infection is associated with scaling. The most common neoplastic condition that causes scaling is mycosis fungoides or the cutaneous form of lymphoma.