Acanthosis Nigricans is a "blackening" of the skin, not just found in dogs, but in humans as well. According to the Merck Vet manual, technically, acanthosis nigricans describes a clinical reaction pattern in dogs characterized by axillary and inguinal hyperpigmentation, lichenification, and alopec.
This skin disease is almost always seen in the Dachshund. Hair loss is a common outcome. Severely affected dogs will have a smelly odor from the progression of the disease. There are many areas on the dog where the disease migrates, such as the stomach, chest, groin, anus, front limbs and hocks.
Signs of acanthosis nigricans are an irregular black thickening and hair loss.
Primary acanthosis nigricans is rare and occurs almost exclusively in Dachshunds. The disease doesn't focus on a particular sex and signs are evident by one year old. Primary acanthosis nigricans in Dachshunds is not curable. Skin scrapings should be performed to rule out demodicosis (red mange), especially in young dogs.
Causes range from conformational abnormalities, obesity, and endocrinopathies (eg, hypothyroidism, hyperadrenocorticism, sex hormone abnormalities) to axillary and inguinal pruritus associated with atopy, food allergy, contact dermatitis, and skin infections.
Secondary acanthosis nigricans is relatively common and can occur in any breed of dog.
The edges of the lesions are often erythematous (an inflammatory, infectious tissue disease). As the lesions progress, secondary alopecia, seborrheic dermatitis, and infections (staphylococcal or Malassezia dermatitis) develop.
Can Acanthosis Nigricans be treated and if so, how?
Usually early in the process injectable, oral, and topical steroids can be effective forms of treatment. According to Go Pets, early cases may respond to shampoo therapy and local topical glucocorticoids, eg, betamethasone valerate ointment.
With the disease the skin can develop a crusty layer and can be treated with antibiotics, weight reduction and medicated shampoos to smooth the skin and remove crusts. Antiseborrheic shampoos are often beneficial for removing excess oil and odor. In addition, the hormone melatonin can be very effective in reversing and preventing the condition.
As lesions progress, more aggressive systemic therapy may be useful, to include vitamin E, 200 IU for 2-3 mo; systemic glucocorticoids, 1 mg/kg for 7-10 days; on alternate days, melatonin, 2 mg/dog for 3-5 days, then weekly or monthly as needed.
In secondary acanthosis nigricans, the lesions will spontaneously resolve after identification and correction of the underlying cause. Secondary bacterial and yeast pyodermas must be treated appropriately. Cephalexin (30 mg/kg, PO, bid) and concurrent itraconazole or ketoconazole (5-10 mg/kg, PO, sid) is an effective treatment regimen. Affected dogs benefit greatly from appropriate antimicrobial therapy and antiseborrheic shampoos (2-3 times/wk).
Other ways to diagnose the disease are smears, endocrine function tests for thyroid and adrenal, intradermal skin testing and food trials.
In addition, skin biopsies may be helpful to identify secondary bacterial infections. The goal of all treatment is to terminate the underlying disease process.
Why is the disease prevalent in Dachshunds?
The disease is usually caused by friction. Since Dachsunds have very short legs and deep chests the skin fold in the armpit can be continuously irritated, eventually turn red, and over time become darker and turn black.
What is the difference between Dermatitis and Ancanthosis Nigricans?
Dermatitis is red, flaky skin, with cracks or tiny blishters and is extremely itchy. In comparison, Ancanthosis Nigricans is brown to black, poorly defined, velvety hyperpigmentation of the skin, usually present in the posterior and lateral folds of the neck, the axilla, groin, umbilicus, and other areas.
Clinical signs resolve slowly, possibly over time. The disease is mainly found in Dachshunds and in human patients with Type 2 Diabetes.
Ackerman, L. Skin and Haircoat Problems in Dogs. Alpine Publications. Loveland, CO; 1994
Scott, D; Miller, W; Griffin, C. Muller and Kirk's Small Animal Dermatology. W.B. Saunders Co. Philadelphia, PA; 1995.