Acanthosis nigricans is hyperpigmentation of a dog's skin. As a secondary disorder, it can appear in any breed at any age.
Causes: Inherited or Acquired
Veterinary science is unsure about the cause of the inherited form of acanthosis nigricans, but it's believed that the inheritance is either autosomal recessive or polygenic, according to the authors of "Muller and Kirk's Small Animal Dermatology." Polygenic inheritance refers to a condition or characteristic that is controlled by two or more genes. Autosomal recessive describes the way many disorders are passed down: A pup who develops acanthosis nigricans has two copies of a defective gene, while a pup with one defective gene is just a carrier. Breeds who develop it as a secondary condition are those with a tendency to develop skin inflammation in the groin, folds between the legs and the trunk, obesity, dermatitis, underactive thyroid and food allergies.
Typically, the condition appears as a darkening of the skin in the creases at the top of the legs or in the groin. The hair eventually falls out, leaving a dark, leathery patch of skin. Such patches usually become inflamed as the condition develops and get worse if left untreated. Yeast or bacterial infections may also take hold and cause itching that the dog scratches, causing the skin problem to get worse. The patches can also be smelly and painful for your pup.
It is fairly easy for a veterinarian to recognize the disease, but he will want to examine the dog and take a full history to find the underlying cause in the case of a dog who has acquired acanthosis nigricans as a secondary condition. The vet may take skin scrapings, test the thyroid and adrenal functions, and do a food allergy test. Dogs who have inherited the condition don't require the same amount of testing as other breeds, and a diagnosis is based on the typical appearance of the disease.
Dogs who have inherited acanthosis nigricans can't be cured, but you can manage the condition with anti-sebhorreic shampoo, vitamin E oil, melatonin and corticosteroids if needed. Your vet will prescribe a treatment regime. Dogs who have acquired the problem also benefit from using antimicrobial shampoo and vet-prescribed topical ointments. Your vet may suggest a regimen of melatonin, vitamin E and systemic glucocorticoids, which are a cortisone-based treatment for both canines and humans with dermatitis. The condition should disappear over time, but it may take months.