Which of the following is the most common metabolic cause of acanthosis nigricans?

Explanation

## Metabolic Causes of Acanthosis Nigricans **Key Point:** Insulin resistance is the most common metabolic cause of acanthosis nigricans, accounting for the majority of non-malignant cases. This is strongly associated with type 2 diabetes mellitus, obesity, and polycystic ovary syndrome (PCOS). ### Classification of Acanthosis Nigricans by Etiology | Type | Cause | Frequency | Key Features | | --- | --- | --- | --- | | Insulin-resistant | Type 2 DM, obesity, PCOS, acromegaly | Most common (90%) | Associated with hyperinsulinemia | | Malignant | Gastric, lung, breast, ovarian cancers | 5–10% | Sudden onset in adults; rapid progression | | Drug-induced | Nicotinic acid, corticosteroids, oral contraceptives | Rare | Resolves with drug withdrawal | | Idiopathic | Unknown | Rare | Benign course | **High-Yield:** The insulin resistance form is by far the most common presentation in clinical practice. Hyperinsulinemia stimulates insulin-like growth factor (IGF-1) receptors on epidermal cells, promoting proliferation and pigmentation. **Clinical Pearl:** In a young obese patient with acanthosis nigricans, metabolic screening (fasting glucose, HbA1c, lipid profile) and evaluation for PCOS should precede malignancy workup. The presence of acanthosis nigricans is a clinical marker of insulin resistance even before overt diabetes develops. **Mnemonic:** **ACANTHOSIS causes** — **A**canthosis from **I**nsulin resistance (most common), **M**alignancy, **D**rugs, **I**diopathic. ### Pathophysiology of Insulin-Resistant Form 1. Hyperinsulinemia → increased IGF-1 signalling 2. Stimulation of epidermal growth factor receptors 3. Keratinocyte proliferation and increased melanin synthesis 4. Papillomatosis and velvety thickening of skin