Alopecia areata means “an area of hair loss.” The condition is presumed to be due to an immune-mediated attack on growing hair follicles. This is most often seen as a patch of hair loss on smooth skin that doesn’t seem to be inflamed. In people, there is at least circumstantial evidence that the disorder is autoimmune in nature, and this theory has been extended to dogs (rightly or wrongly). Actually, alopecia areata is not a dangerous disorder at all and it really represents a patch of baldness with no health risk.
The diagnosis can be confirmed by biopsy if the samples are sent to a pathologist with expertise in disorders of the skin. The biopsies show a collection of white blood cells (lymphocytes) preying on growing hair follicles. Once the hair follicle goes into a resting stage, any inflammation that might have occurred subsides. This leaves a patch of smooth skin without hair. Biopsies are important, because other diseases (e.g., ringworm, bacteria, rabies vaccination sites) may look quite similar yet are treated quite differently. Interestingly enough, after the inflammation has subsided, the lack of growing hair follicles is very similar to conditions produced by hormonal disorders such as hypothyroidism, and this mistaken diagnosis may be made if the pathologist is not provided with accurate clinical information.
For the most part, alopecia areata is not treated, since it really doesn’t affect the health of the dog. Since increasing the blood supply to the hairless patch of skin may cause the follicles to go back into a growth phase, using a mildly abrasive brushing technique (for many weeks or months) may stimulate the hair to grow in the affected areas. Injections of corticosteroids may also cause hair to grow, but treatment must not be excessive or the side affects may be more troublesome than the disease itself. Minoxidil (Rogaine), used in the treatment of male pattern baldness, has also been used for alopecia areata but is not licensed for treatment of dogs.”
To learn about other Immune-mediated skin diseases, read Lowell Ackerman’s informative book, Guide to Skin and Haircoat Problems in Dogs .