Alopecia in cats is one of the most frustrating problems I have to deal with as a veterinarian because there are so many things that can cause it. To help narrow down the possible causes, I want to know if the cat actually pulls their hair out while grooming or if the hair falls out by itself. Since some cats are ‘closet groomers’, their humans might not see them in action. So I start the workup by examining hair under the microscope to see if the shafts are broken. This indicates chewing if they are broken or if intact it indicates the hair fell out. In my experience, alopecia in young cats is the former while alopecia in older cats is the latter.
Young cats can react to stress from pain or a constant itch by chewing. The most common causes are mites, ringworm, fleas, abdominal pain, intestinal parasites and food allergies. Many tests including skin scrapes, a fecal analysis, blood work, fungal culture and urinalysis are needed for the proper diagnosis. In older cats where the hair falls out on its own, I worry about paraneoplastic syndrome. That’s a fancy way of saying cancer. For these cases, a biopsy of the hairless area is usually the quickest way to make a diagnosis.
Notice, the cat pictured below has alopecia between its eyes and ears. This is a normal area of alopecia that is not a medical problem.
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http://www.ehow.com/video_12300345_alopecia-cats.html