Acanthosis Nigricans
A skin condition characterized by areas of dark, velvety hyperpigmentation in body folds and creases. It is frequently a cutaneous marker for underlying systemic disease.
Key Clinical Features
- Appearance: Hyperpigmented, “velvety” plaques.
- Distribution: Most commonly found on the back of the neck, axillae, groin, and intermammary folds.
Etiology: The “Big Two”
| Type | Associations |
|---|---|
| Benign | Insulin resistance (Type 2 Diabetes, Obesity, PCOS, Metabolic Syndrome). |
| Malignant | Rapid onset, extensive distribution (including palms/mucosa). Classically associated with gastric adenocarcinoma. |
High-Yield Exam Pearl:
- Pathophysiology: High levels of insulin (or IGF-1 in malignancies) bind to fibroblast growth factor receptors (FGFRs) on keratinocytes, promoting cellular proliferation.
- Red Flag: Any sudden, extensive appearance of Acanthosis Nigricans in a patient who is *not* obese or diabetic should trigger an immediate workup for internal malignancy.