**Core Concept**
Lucio's phenomenon is a rare and severe complication of leprosy characterized by necrotizing vasculitis, leading to ischemic necrosis of the skin. It is often associated with the lepromatous form of leprosy, which is a more aggressive and disseminated form of the disease.

**Why the Correct Answer is Right**
Lucio's phenomenon is caused by the activation of immune cells, such as macrophages and T lymphocytes, in response to the leprosy bacillus (Mycobacterium leprae). This activation leads to the release of cytokines and other inflammatory mediators, resulting in the damage of small and medium-sized blood vessels. The ischemic necrosis of the skin occurs as a result of the impaired blood flow to the affected areas. The phenomenon is often accompanied by fever, malaise, and other systemic symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Lucio's phenomenon is not typically associated with tuberculoid leprosy, which is a less aggressive form of the disease characterized by a strong cell-mediated immune response.
**Option B:** While Lucio's phenomenon can occur as a complication of leprosy treatment, it is not a side effect of treatment per se, but rather a manifestation of the underlying disease process.
**Option D:** Lucio's phenomenon is not known as a type 2 Lepra reaction. Type 2 Lepra reaction, also known as erythema nodosum leprosum (ENL), is a different type of immune-mediated reaction that occurs in leprosy patients, characterized by the formation of tender nodules and other systemic symptoms.

**Clinical Pearl / High-Yield Fact**
Lucio's phenomenon is a medical emergency that requires prompt recognition and treatment to prevent further tissue damage and complications. It is essential for clinicians to be aware of this rare but severe complication of leprosy to provide timely and effective management.

**✓ Correct Answer: C. Ischemic necrosis**