M.C. type of cutaneous T.B. is –
**Core Concept**
Cutaneous tuberculosis (TB) is a form of extrapulmonary TB that affects the skin. There are several types of cutaneous TB, each with distinct clinical presentations and pathologies. The most common types are scrofuloderma, lupus vulgaris, and tuberculids.
**Why the Correct Answer is Right**
Mantoux-type cutaneous TB, also known as tuberculid, is a type of cutaneous reaction to an internal focus of TB infection. It is characterized by the appearance of papules, plaques, or nodules on the skin, often in response to a systemic infection. The exact mechanism is not fully understood, but it is thought to involve an immune-mediated reaction to the TB antigens.
**Why Each Wrong Option is Incorrect**
* **Option A:** Scrofuloderma is a type of cutaneous TB that results from direct extension of TB from an underlying bone or joint, typically the cervical spine. It presents as firm, painless nodules or plaques on the skin.
* **Option B:** Lupus vulgaris is the most common form of cutaneous TB, accounting for about 70% of cases. It presents as chronic, progressive lesions on the face, neck, or upper trunk.
* **Option C:** Erythema induratum is a type of tuberculid that affects the lower legs, presenting as painful nodules or plaques.
**Clinical Pearl / High-Yield Fact**
Tuberculids are a type of cutaneous TB reaction that can occur in the absence of any visible skin lesions, making them a challenging diagnosis.
**Correct Answer: D. Mantoux-type cutaneous TB, also known as tuberculid.**