**Core Concept:** Erythema multiforme (EM) is a skin reaction characterized by the appearance of target-like lesions, associated with fever, malaise, and mucosal involvement. It is classified into four types: minor, major, drug-induced, and systemic. EM is typically caused by an immune-mediated response to various triggers such as infections, drugs, or allergens.

**Why the Correct Answer is Right:** Type II hypersensitivity reaction is the primary mechanism underlying erythema multiforme. The reaction involves the activation of cytotoxic T-cells that release granzymes and perforin, leading to apoptosis (cell death) of keratinocytes in the basal layer of the epidermis. This results in the characteristic target-like lesions seen in EM. The reaction is also associated with fever, malaise, and mucosal involvement due to the systemic nature of the immune response.

**Why Each Wrong Option is Incorrect:**

A. **Erythema multiforme minor (EM minor):** This is a mild form of EM characterized by macules and papules without mucosal involvement. The incorrect answer is due to the presence of mucosal involvement in EM major.

B. **Erythema multiforme major (EM major):** This is a severe form of EM characterized by mucosal involvement and bullae formation. While the correct answer mentions mucosal involvement, the incorrect answer does not address the bullae formation in EM major.

C. **Erythema multiforme drug-induced:** EM can be triggered by various drugs, but the correct answer does not specify a particular drug as the cause.

D. **Systemic sclerosis:** This is a separate disease characterized by fibrosis and sclerosis of the skin and internal organs, with different pathophysiology and clinical presentation than EM.

**Clinical Pearl:** Erythema multiforme is a crucial clinical entity to recognize as it can be associated with severe complications, including mucosal ulceration, dysphagia, and respiratory distress. Prompt diagnosis and management are essential to minimize these complications and ensure patient safety.