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 disorders

Disorders 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.

Treatment

Treatment for the keratinization disorder involves treating the underlying cause for the scaling if possible. Topical antiseborrheic shampoos and sprays are useful. Also, fatty acids that contain both omega 3 and omega 6 fatty acids are most beneficial. Topical anti-seborrheic products such as Dermoscent Omega 6 fatty acid and Sogeval Douxo Antiseborrhea products are useful new adjuvant treatment for controlling seborrhea. You should start to see improvement in the skin and hair coat with fatty acid supplementation within 1 to 2 months. If you do not see any improvement in 2 months. In cases of nutritional keratinization disorders, supplementation with the nutrient (i.e. retinol in the case of vitamin A responsive dermatosis and zinc methionine in the case of zinc responsive dermatosis) provides clinical benefit within the first 3 months of starting the treatment.

If allergies are causing the scaling then the allergy needs to be identified and controlled. The offending food ingredient or ingredients need to be avoided in the case of food allergies. Atopic dermatitis is controlled with immunotherapy or steroids or antihistamines or cyclosporine. Contact allergies are treated by identifying and avoided the offending contact allergen. Flea allergies are controlled by using flea medication that prevents the immature and adult stages of the flea cycle. Periodic flare ups of the seborrhea may occur if the allergies are not under control.

If parasites are present and causing the seborrhea then the seborrhea will continue until the parasites are controlled. The parasitic treatment will depend on the parasite being treated. Many of the parasites with the exception of demodex can be treated with lime sulfur dips. However, the odor of this dip is offensive for many owners and most owners would prefer a systemic over a topical treatment. Examples of topical medications to treat mites include: selamectin, fipronil, moxedectin and mitaban. It is important to note that the only topical in this list that treats demodex effectively is the mitaban. Oral antiparasiticidal medications such as ivermectin and milbemycin have also been used.

Fungal skin infections can be treated with topical antifungal medications as well as systemic antifungal medications. The most commonly used antifungal agents are the azoles. Treatment should be continued until a negative culture is obtained. This means that the pet is treated for a minimum of 1 month.

Hormonal causes for seborrhea need to be identified and treated. Levothyroxine is used to treat hypothyroidism. Mitotane, ketoconazole or trilostane have been used to treat pituitary dependent hyperadrenocorticism. Adrenal dependent hyperadrenocorticm is treated by surgically removing the adrenal tumor. These animals are supplemented with mineral corticocoids and glucocorticoids post-operatively. Sex hormone alopecias may need to be treated with mitotane or sex hormones depending on the clinical diagnosis.

Inherited causes for seborrhea are a challenge for pet owners. One of the problems with this type of seborrhea is that these cases often get secondary bacterial and/or fungal skin infections. Bathing with antimicrobial shampoos on a regular basis can be beneficial. It is important to remind the pet owners that since this problem is genetic, offspring of their pet can get a similar dermatologic condition. Therefore, a responsible breeder would have these pets spayed or neutered before they are allowed to breed.

Comments and conclusions

A wide variety of medical conditions cause scaling disorders in dogs. Some of the cases of scaling can be controlled when the underlying cause or reason is addressed (i.e. most cases of secondary seborrhea or keratinization disorders). If the underlying cause for the scaling is primary or idiopathic then several medications can be used to try to control the scaling but the problem for the pet will be lifelong. Therefore, it is important for the pet owner to know which type of scaling disorder are present (primary verses secondary) and the underlying etiology. This is the only way that the owner will be informed of the prognosis for their pet.

Selected readings

Power HT, Ihrke PJ. The use of synthetic retinoids in veterinary medicine. In Bonagura JD (ed): Kirk's Current Veterinary Therapy XII. WB Saunders Co, Philadelphia, 1995, p. 585.

Baker, BB, Maibach, HI. Epidermal cell renewal in seborrheic skin of dogs. Am J Vet Res 48:726, 1987.

Kwochka KW, Rademakers AM. Cell proliferation kinetics of epidermis, hair follicles, and sebaceous glands of Cock spaniels with idiopathic seborrhea. Am J Vet Res 50: 1918, 1989

Muller GH. Ichthyosis in two dogs. J Am Vet Med Assoc 169:1313, 1976.

Scott D. Congenital and hereditary defects. In Scott DW, Miller WH, Griffin CE. Saunders, Philadelphia 2001, pp. 913-1003.