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The management of common dermatological problems in older dogs (Proceedings)

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Aug 01, 2010

To the owner, integument changes are the most obvious sign of aging. Aging of the skin and adenexa is a complex subject influenced by a combination of interrelated causative factors including wear and tear, cumulative cell damage from ionizing irradiation, and genetically preprogrammed cell changes.

The decrease in the number of active hairs and the follicular atrophy results in a thinner hair coat. Graying of the hairs especially on the muzzle is a result of the decrease in melanocyte replication. The nails become longer, malformed and more brittle. There is a progressive hyperkeratosis of the skin and hair follicles. This is especially obvious on the patient's foot pads and nose. The application of keratolytic agents or softeners is usually helpful in managing this problem. The altered sebum production and cystic dilation of the apocrine glands results in a dry, lack luster hair coat and dry skin. The dryness of the skin and coat can be helped with increased grooming, less bathing, post bathing conditioners, topical emollient (oils) and/or humectants (moisture) sprays, and essential fatty acid nutritional supplements.

Senior patients are to be more prone to food allergies, endocrine-related skin changes, pressure point calluses, adult onset Demodecosis, and cutaneous neoplasia. Sebaceous gland tumors "senile warts" account for up to 35% of all canine skin tumors but are rare in cats. They can be single but are usually multiple and occasionally ulcerate. Rarely they do they become malignant. Clinical management options include surgical excision, crysotherapy, electro surgery, laser surgery and topical chemotherapy agents including 5 FU.

Because of decreases in cellular immunity, except for fleas and ticks, infectious diseases of the skin continue to be the most common skin disease of older pets. Recurrent bacterial folliculitis, pyoderma, or otitis externa can be problematic in the older pet. The use of antiseptic shampoos, antiseptic rinses, and long term / low dose chronic antibacterial therapy is often required to manage the problem.

In older patients, Demodecosis is not usually considered in the differential diagnosis of a skin problem, but adult-onset demodex does occur and is often missed because of omitting a skin scraping in the work up. Remember demodex is a great imposer and can look like a pyoderma, an allergy, a dermatophytes infection, and even an auto-immune skin disease. The decreased cell mediated immunity may also suppress the usual inflammatory changes. With generalize adult-onset Demodecosis cases, some underlying immunosuppressive systemic disease such as Hyperadrenalcorticism, hypothyroidism, renal failure, diabetes mellitus, or neoplasia should be ruled out.

In an older dog with a late onset of pruritic skin disease, food should be strongly considered. Food allergy and food hypersensitivity are terms used to describe the immunological mediated disease reaction induced by food ingestion. Conversely food intolerance is the term used for an abnormal physiological response of foods or food additives that does not have an immunological basis. In a clinical setting, food hypersensitivity and food intolerance are rarely differentiated and refer to a non-seasonal pruritis skin disorder associated with ingestion of a substance usually found in the diet. Numerous dietary allergens exist including beef, pork, chicken, cows' milk, horsemeat, chicken egg, wheat, oats, fish, corn, and soy protein. Although any dietary protein is capable of causing pruritis, beef, dairy products, wheat and soy proteins are the most common cause of adverse cutaneous reactions. Dogs and cats can react to one or more dietary allergens.

Non-seasonal pruritis is the most common clinical sign in dogs with food-related dermatitis. In dogs the age of onset of food-related dermatitis is variable, however if the onset is in a senior dog with no previous "allergic" history, food-related allergy is much more likely that atopy. Unfortunately, the onset of food-related dermatitis is not usually associated with a recent change in diet. In one study 68% of dogs had been fed the offending diet for at least two years before onset of clinical signs. Dogs with food-related dermatitis generally will not respond as well to conventional anti-inflammatory doses of glucocorticoids, cyclosporine, antihistamine therapy, or essential fatty acid supplements as dogs with most other allergic diseases (i.e. atopy, FAD). Therefore the lack of response to these medications in a dog with mild to moderate pruritis would make Atopic dermatitis less likely than food-related dermatitis.