**Question:** Sub-epithelial humps are characteristic of -

A. Lichen planus
B. Pemphigus vulgaris
C. Erythema multiforme
D. Erythema nodosum

**Core Concept:** Sub-epithelial humps are a histopathological feature observed in certain dermatological conditions, which represent the subepidermal mucin deposition and thickening of the basement membrane zone.

**Why the Correct Answer is Right:**

Sub-epithelial humps are observed in Pemphigus vulgaris, an autoimmune disease characterized by the presence of autoantibodies targeting desmoglein proteins in the epidermal-dermal junction. This leads to subepidermal mucin deposition and blister formation.

**Why Each Wrong Option is Incorrect:**

A. Lichen planus: Though lichen planus is a dermatological condition, sub-epithelial humps are not a characteristic feature of this disease. Lichen planus is characterized by the presence of koilocytes, interface dermatitis, and basal cell layer atrophy.

B. Pemphigus vulgaris is the correct answer, as mentioned earlier, due to subepidermal mucin deposition and autoantibodies targeting desmoglein proteins.

C. Erythema multiforme is a dermatological condition characterized by mucosal involvement and symmetric targetoid lesions. Sub-epithelial humps are not a feature of this condition.

D. Erythema nodosum is characterized by subcutaneous inflammation and nodules, not sub-epithelial humps. Subepithelial humps are not a feature of this condition.

**Clinical Pearl:** Sub-epithelial humps are essential to differentiate between autoimmune bullous diseases, such as pemphigus, and other dermatological conditions. A thorough knowledge of histopathological features is crucial in making an accurate diagnosis in dermatology.

**Correct Answer:**

D. Erythema nodosum

**Why the Correct Answer is Right:**

Erythema nodosum is a type of dermatological condition characterized by subcutaneous inflammation and nodules, which are the key histopathological feature present in this condition. Sub-epithelial humps are not present in Erythema nodosum.

**Why Each Wrong Option is Incorrect:**

A. Lichen planus: Lichen planus is characterized by subepidermal mucin deposition and autoantibodies targeting desmoglein proteins, not subcutaneous inflammation and nodules.

B. Pemphigus vulgaris: Pemphigus vulgaris is characterized by subepidermal mucin deposition and autoantibodies targeting desmoglein proteins, not subcutaneous inflammation and nodules.

C. Erythema multiforme: Erythema multiforme is characterized by symmetric targetoid lesions, not subcutaneous inflammation and nodules.

D. Erythema nodosum is characterized by subcutaneous inflammation and nodules, not sub