Acral Acanthosis Nigricans (AAN) is a rare and typically benign skin condition that presents as hyperpigmented, thickened, velvety patches on the skin — specifically on the acral areas (i.e., the extremities like the hands, feet, fingers, and toes).
Key Features of Acral Acanthosis Nigricans
| Feature | Description |
|---|---|
| Location | Dorsal surfaces of hands, feet, fingers, and toes |
| Appearance | Hyperpigmented (brown to black), thickened, velvety plaques |
| Onset | Usually gradual and asymptomatic |
| Symptoms | Generally asymptomatic, may have mild pruritus (itching) in some cases |
| Histology | Similar to other forms of acanthosis nigricans: papillomatosis, hyperkeratosis, and acanthosis |
Causes and Associations
Acral Acanthosis Nigricans is often classified as benign and is not typically associated with internal malignancies, unlike the malignant form of AN.
Common associations include:
Ethnicity:
More prevalent in individuals with darker skin tones, particularly of African descent.
Genetic Predisposition:
Can be idiopathic or familial.
Endocrine Associations:
Less commonly associated with insulin resistance or metabolic syndrome than other AN variants.
Drug-Induced:
Rarely, can be associated with medications (e.g., nicotinic acid, insulin, or corticosteroids).
Differential Diagnosis
Malignant Acanthosis Nigricans (usually involves mucosa and is more widespread)
Confluent and Reticulated Papillomatosis
Lichen Planus
Tinea nigra
Post-inflammatory hyperpigmentation
Management
Since AAN is often benign and cosmetic, treatment is generally not required unless for aesthetic or symptomatic reasons.
Options include:
Topical keratolytics (e.g., salicylic acid, urea)
Topical retinoids (e.g., tretinoin)
Laser therapy (for cosmetic purposes)
Treating underlying causes (if identified)
Prognosis
Usually benign with a stable or slow progression.
Not considered a marker for malignancy or systemic disease in most cases.