Skin care: Acanthosis Nigricans

Breeds affected: Dachshund. This is a rare disease of unknown cause seen exclusively in Dachshunds. It begins with subtle symmetrical hyperpigmentation in the armpits. The early lesions then progress slowly to hair loss. Greasy, smelly debris accumilate in more severely affected dogs. The abdomen, groin, chest, anal area, forelimbs and hock may all be involved.

Acanthosis nigricans describes a clinical reaction pattern in dogs characterized by axillary and inguinal hyperpigmentation, lichenification, and alopecia.
Acanthosis nigricans is a clinical sign, not a diagnosis. The pathogenesis is poorly understood, but clinical signs are dachshund_skin_probleminvariably 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.

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.
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.
Treatment:
– The main aim of treatment of Acanthosis Nigricans lies in terminating the underlying disease process.
– Treatment of the lesions of acanthosis nigricans is for cosmetic reasons only.
– Correcting hyperinsulinemia may also help control the condition.
– If the condition is caused due to an external cause like the side effect of a medication, it will go away once the medicine is stopped.

Primary acanthosis nigricans
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.

Secondary acanthosis nigricans
The secondary form of the disease is much more common. The darkening of the skin occurs because of one of three underlying conditions. 1) Friction caused by obesity or conformational abnormalities. 2) Endocrine imbalances including hyperthyroidism, Cushing is disease, or sex hormone imbalances. 3) Hypersensitivities due to food, inhalant (atopy), or contact allergies.
In addition to blackening of the skin, secondary acanthosis nigricans is often associated with chronic hair loss and/or itching and other skin problems. If an owner sees these skin conditions developing, she should have the dog examined by a veterinarian and the underlying cause of the condition should be identified.
The treatment for secondary acanthosis nigricans usually consists of treating the underlying condition, e.g., through weight loss, thyroid medication or allergy relief. In more severe cases, steroid therapy at low doses has helped to reduce inflammation in the skin. In addition, Vitamin E supplementation has shown to help in the recovery of some cases,  but offers a relatively-nontoxic aid to therapy. The majority of time the condition will improve once the underlying condition has been identified and properly treated.

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