Hyperpigmentation is a darkening and thickening of the skin seen in dogs. It is not a specific disease but a reaction of a dog’s body to certain conditions.
Hyperpigmentation appears as light-brown-to-black, velvety, rough areas of thickened, often hairless skin. The usual sites are in the legs and groin area. It can be primary or secondary. Primary diseases that cause hyperpigmentation can occur in any breed but especially Dachshunds. Signs are usually evident by 1 year of age. Secondary hyperpigmentation is relatively common and can occur in any breed of dog, most commonly those breeds prone to obesity, hormonal abnormalities, allergies, contact dermatitis, and skin infections. Secondary hyperpigmentation is triggered by inflammation and/or friction. Inflammation leads to additional skin changes, such as thickened skin, hair loss, odor, and pain.
The edges of inflamed areas are often red, a sign of secondary bacterial or yeast infection. With time, it may spread to the lower neck, groin, abdomen, hocks, eyes, ears, and the area between the anus and the external genital organs. Itching is variable. When it occurs, it may be caused by the underlying disease or by a secondary infection. As the condition progresses, secondary hair loss, fluid discharge, and infections develop.
Diagnosis is by appearance of signs on the animal. In a young Dachshund, your veterinarian will want to eliminate other causes of the signs. A careful history and physical examination will be performed to identify an underlying cause. The presence of secondary hyperpigmentation always suggests an underlying disease. Skin scrapings are taken to exclude other causes (parasites, for example), especially in young dogs. Impression smears are used to identify bacterial infections. Depending on other signs, endocrine function tests for thyroid and adrenal disease may be used to check for underlying hormonal abnormalities. Skin testing, a food trial, or both may be necessary to test for allergies. Skin biopsies may be made to check for a condition called seborrhea. In most cases, your veterinarian will want to treat any secondary bacterial infections before proceeding with other diagnostic tests.
Primary hyperpigmentation in Dachshunds is not curable. In some dogs, the condition is only cosmetic and does not require treatment. If inflammation is present, early cases may respond to shampoo treatment and steroid ointments. As signs progress, other treatment, such as medication given by mouth or injection, may be useful. The concurrent treatment of secondary infections is helpful and is required before steroids are administered. Medicated shampoos are often beneficial for removing excess oil and odor but must be used regularly.
In secondary hyperpigmentation, the affected areas will go away on their own after identification and treatment of the underlying cause. However, this will not occur if secondary bacterial and yeast infections are not treated and controlled. Many affected dogs benefit greatly from appropriate antibiotics and medicated shampoos (2 to 3 times per week). Thus, many veterinarians will prescribe such treatments. Owners need to be patient with these treatment programs. The signs of hyperpigmentation resolve slowly; it may take months for the dog’s skin to return to normal.
Also see professional content regarding acanthosis nigricans.