## **Core Concept**
The question tests knowledge of dermatological conditions that present with specific systemic and cutaneous manifestations, particularly focusing on itchiness, mucosal involvement, and nail changes.

## **Why the Correct Answer is Right**
Psoriasis is a chronic autoimmune skin condition characterized by **hyperproliferation of keratinocytes**, leading to thickened skin, scales, and erythema. It often presents with **pruritus (itchiness)**, and can affect **mucosal surfaces** (e.g., oral, genital) as well as **nails**, causing pitting, onycholysis (separation of the nail from the nail bed), and subungual hyperkeratosis.

## **Why Each Wrong Option is Incorrect**
* **Option A:** While eczematous dermatitis (atopic dermatitis) can be itchy and sometimes affect the nails, it primarily involves the skin and not typically the mucosa in a significant way.
* **Option B:** Lichen planus can involve mucosa and nails and present with itchy skin lesions, but its primary characteristics are **violaceous polygonal papules** and **mucous membrane lesions**.
* **Option C:** Pemphigus vulgaris primarily affects the skin and mucosa with **flaccid bullae** but does not commonly cause itchiness or nail changes as primary features.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **psoriasis** can have a significant impact on quality of life due to its disfiguring skin lesions, itchiness, and systemic associations (e.g., psoriatic arthritis). A classic exam trap is to confuse it with other dermatological conditions like eczema or lichen planus; however, the combination of itchiness, mucosal involvement, and specific nail changes makes psoriasis a standout diagnosis.

## **Correct Answer:** D. Psoriasis.