Section: Veterinary Care In-depth
Diagnosis In-depth
History and physical examination are important in the diagnosis of the underlying cause of miliary dermatitis. The veterinarian will ask when the problem started, whether the cat is scratching, chewing or grooming excessively, and whether the cat feels well or feels sick. The physical exam will look at all body systems, but will concentrate on the skin. The distribution of lesions on the body may lend important clues to the underlying cause. A flea comb will be used to look for fleas and flea dirt.
Skin scrapings are very important to assess for parasites. A scalpel blade is used to scrape a sample from the surface of the skin. Deep skin scrapings are needed to find mites, so your veterinarian will scrape until there is mild bleeding. The sample is then examined under a microscope for mites or other parasites.
A fungal culture is often done to rule out ringworm. Hairs are plucked from lesions and are incubated on a special media. The dermatophyte that is most commonly seen in cats will fluoresce sometimes in ultraviolet light, so your veterinarian may examine the cat's hair in a dark room with a special light called a Wood's lamp. A lime-green fluorescence of hair shafts confirms the diagnosis and makes culture unnecessary.
A trichogram is a test where hairs are plucked and examined under a microscope to determine if hairs are falling out, or being broken off. With miliary dermatitis due to an itchy disease, hairs appear broken off due to the self-mutilation. This test may help to determine if a pruritic disease should be pursued.
A food trial should be done if miliary dermatitis continues after the above diseases have been rule out. Food allergy is ruled out by feeding a diet that contains ingredients that the cat has not been previously fed. This diet is fed as the only food source for a period of 6-12 weeks or until the cat stops itching. Individual ingredients from the previous food may then be fed to identify the offending ingredient.
Allergy testing for airborne allergens such as pollens, molds, house dust, and house dust mites may be necessary. The most accurate test in a skin test where different airborne allergens are injected into the skin and the skin is then examine to see if it reacts. A blood test is also available that is more convenient and easier but may not be as accurate.
A skin biopsy may help to narrow down the type of disease causing miliary dermatitis. After general or local anesthesia, one or more sections of skin are taken from the cat using either a special biopsy punch or a scalpel blade. Examination of the biopsy by a veterinary pathologist can categorize the problem as allergic, parasitic, fungal, bacterial, autoimmune or hormonal. More specific tests to confirm the exact diagnosis can then be done.
Blood tests may be needed if the cat is sick to assess the underlying immune problem. Blood chemistry profiles can help rule out diseases of major organs like the liver and kidney. A CBC will assess the health of red blood cells, white blood cells and platelets, and may show evidence of infection or immunosuppression. Viral diseases such as feline leukemia virus and feline immunodeficiency virus should be tested for and ruled out.
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