**Question:** Samitz sign in nails is characteristically seen in

A. psoriasis
B. fungal infections
C. pemphigus vulgaris
D. lichen planus

**Core Concept:** Samitz sign is a clinical feature observed in certain nail disorders, specifically revealing nail dystrophy and nail bed inflammation.

**Why the Correct Answer is Right:** Samitz sign is a clinical feature observed in patients with nail disorders, particularly in cases of pemphigus vulgaris (PV). PV is a group of autoimmune diseases characterized by blistering of the skin and mucous membranes. In PV, there is a loss of adhesion between keratinocytes, leading to blistering and erosions.

**Why Each Wrong Option is Incorrect:**

A. Psoriasis: Although psoriasis can affect nails, Samitz sign is not a characteristic feature in psoriasis. Psoriasis causes nail dystrophy but typically shows nail bed sparing.

B. Fungal infections: Samitz sign is not a common feature in fungal infections affecting the nails. Fungal infections primarily cause nail dystrophy without significant nail bed inflammation.

C. Lichen planus: Samitz sign is not a typical feature of lichen planus (LP). LP is a chronic inflammatory disease affecting skin, hair, nails, and mucous membranes. LP-related nail changes are characterized by onycholysis (separation of the nail from the nail bed) and pitting (indentations in the nail) but typically spares the nail bed.

**Clinical Pearl:** Samitz sign is a helpful clinical clue for the diagnosis of pemphigus vulgaris. It highlights the importance of considering autoimmune disorders like pemphigus vulgaris in the differential diagnosis of nail disorders presenting with dystrophic changes and inflammatory nail bed involvement.

**Correct Answer:** D. Pemphigus vulgaris

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In summary, Samitz sign is a characteristic feature of pemphigus vulgaris, which is an autoimmune disorder causing nail bed inflammation and dystrophic changes. It is essential for clinicians to recognize this sign during the diagnostic process to differentiate it from other nail disorders like psoriasis, fungal infections, and lichen planus. Samitz sign can guide the clinician to consider autoimmune disorders like pemphigus vulgaris in the differential diagnosis of nail disorders presenting with dystrophic changes and inflammatory nail bed involvement.