**Question:** Acanthosis nigricans histological show –

A. Hyperkeratosis
B. Hyperproliferation of keratinocytes
C. Increased melanin synthesis
D. Collagen deposition

**Core Concept:** Acanthosis nigricans is a dermatological condition characterized by the thickening, darkening, and velvety appearance of the skin, primarily affecting the axillae, neck, and groin regions. It is associated with hormonal disturbances, insulin resistance, or underlying malignancies.

**Why the Correct Answer is Right:** In acanthosis nigricans, the histological changes involve hyperkeratosis (abnormal keratinization), hyperproliferation of keratinocytes (excessive skin cell growth), and increased melanin synthesis (pigmentation). These changes result in the characteristic thickening and discoloration of the affected skin.

**Why Each Wrong Option is Incorrect:** Option D (collagen deposition) is incorrect because collagen is not significantly affected in acanthosis nigricans. Collagen is primarily involved in wound healing and elasticity, while acanthosis nigricans is primarily characterized by hyperkeratosis, hyperproliferation, and melanin overproduction.

**Clinical Pearl:** Acanthosis nigricans is a clinical triad (histological, clinical, and underlying cause) that helps in recognizing the underlying etiology. Histologically, hyperkeratosis and hyperproliferation of keratinocytes are key features. Clinically, it presents as a brownish-black, velvety, macule or plaque on the skin, affecting areas like the axillae, neck, and groin. The underlying cause can be hormonal disturbances (e.g., insulin resistance in obesity), neoplasia (e.g., malignant tumors), or medications (e.g., hormonal therapy). A correct diagnosis requires considering these clinical, histological, and etiological aspects together.

**Correct Answer:** B. Hyperkeratosis and hyperproliferation of keratinocytes (skin cells) are the primary histological features of acanthosis nigricans. Understanding the combination of these histological findings and the clinical presentation helps in identifying the underlying cause, whether hormonal disturbances, neoplasia, or medication use.