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Acanthosis Nigricans: Introduction |  |
| Acanthosis nigricans describes a clinical reaction pattern in dogs characterized by axillary and inguinal hyperpigmentation, lichenification, and alopecia. |
| Etiology and Clinical Findings: |
| Acanthosis nigricans is a clinical sign, not a diagnosis. The pathogenesis is poorly understood, but clinical signs are invariably a result of inflammation due to constant friction and the resultant dermatitis. It can be primary (idiopathic) or secondary. Primary acanthosis nigricans is rare, occurs almost exclusively in Dachshunds, and has no sex predilection; it is considered a genodermatosis. Clinical signs are usually evident by 1 yr of age. Secondary acanthosis nigricans
is relatively common and can occur in any breed of dog, most commonly those breeds predisposed to the following common underlying causes: conformational abnormalities, obesity, endocrinopathies (eg, hypothyroidism, hyperadrenocorticism, sex hormone abnormalities), axillary and inguinal pruritus associated with atopy, food allergy, contact dermatitis, and skin infections (eg, staphylococcal pyoderma,
Malassezia
dermatitis). |
| Clinical signs typically consist of bilaterally symmetric axillary or inguinal hyperpigmentation and lichenification. The edges of these lesions are often erythematous; this is a sign of secondary bacterial and/or yeast pyoderma. With time, lesions may spread to the ventral neck, groin, abdomen, perineum, hocks, periocular area, and pinnae. Pruritus is variable and may be caused by the underlying disease or a secondary infection. As the lesions progress, secondary alopecia,
seborrheic dermatitis, and infections (staphylococcal or
Malassezia
dermatitis) develop. |
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| Diagnosis: |
| The physical findings compatible with a clinical diagnosis of acanthosis nigricans are not difficult to recognize. Primary acanthosis nigricans is a diagnosis of exclusion; acanthosis nigricans in a juvenile Dachshund is not always caused by a genodermatosis. A careful history and physical examination should be performed to identify an underlying cause. Skin scrapings should be performed to rule out demodicosis, especially in young dogs. Impression smears are useful to identify
bacterial and
Malassezia
infections. Depending on the nondermatologic signs, endocrine function tests for thyroid and adrenal disease may be useful; endocrine skin diseases are not pruritic unless accompanied by secondary skin infections. Intradermal skin testing, a food trial, or both may be necessary. Skin biopsies are usually nondiagnostic but may be helpful in some cases to identify secondary bacterial infections not previously recognized. The presence of such infections is common but
often overlooked. In most cases, it is useful to treat the secondary bacterial and/or
Malassezia
infections before proceeding with other diagnostic tests. |
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| Treatment: |
| Primary acanthosis nigricans in Dachshunds is not curable. Early cases may respond to shampoo therapy and local topical glucocorticoids, eg, betamethasone valerate ointment. As lesions progress, more aggressive systemic therapy may be useful. The following systemic therapies have been used, alone or in combination, with varying degrees of success: vitamin E, 200 IU, PO, bid, for 2-3 mo; systemic glucocorticoids, 1 mg/kg, PO, sid for 7-10 days, then
on alternate days; melatonin, 2 mg/dog, SC, sid for 3-5 days, then weekly or monthly as needed. The concurrent treatment of secondary bacterial or
Malassezia
infections is helpful and is required before systemic glucocorticoids are administered; antimicrobial therapy is compatible with the other therapies. Antiseborrheic shampoos are often beneficial for removing excess oil and odor. |
| In secondary acanthosis nigricans, the lesions will spontaneously resolve after identification and correction of the underlying cause. However, this will not occur if secondary bacterial and yeast pyodermas are not 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). |
| Clinical signs resolve slowly, possibly over months. |
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