**Question:** All of the following statements about leprosy are true except -

A. Leprosy is a bacterial infection caused by Mycobacterium leprae and Mycobacterium lepromatosis.
B. Leprosy affects primarily the skin, peripheral nerves, and upper respiratory tract.
C. Leprosy can lead to deformities, such as clawing of fingers and toes.
D. Treatment for leprosy involves a single drug, corticosteroids.

**Correct Answer:** D. Treatment for leprosy involves a single drug, corticosteroids.

**Core Concept:**
Leprosy is a chronic infectious disease caused by Mycobacterium leprae and Mycobacterium lepromatosis. This disease primarily affects the skin, peripheral nerves, and upper respiratory tract, leading to specific clinical manifestations and signs.

**Why the Correct Answer is Right:**
Correct answer D states that treatment for leprosy involves a single drug, corticosteroids. However, this is not accurate as the standard treatment for leprosy is a combination of antibiotics, specifically dapsone, rifampicin, clofazimine, and ofloxacin, depending on the disease severity and type. Corticosteroids are sometimes used for nerve pain relief in leprosy patients but are not the mainstay of treatment.

**Why Each Wrong Option is Incorrect:**
Option A is correct as leprosy is indeed caused by Mycobacterium leprae and Mycobacterium lepromatosis.
Option B is incorrect because leprosy is treated with a combination of antibiotics, not a single drug like corticosteroids.
Option C is partially correct as leprosy does lead to deformities, but it is option D that is incorrect due to its mention of corticosteroids as the primary treatment, which is not the case.

**Clinical Pearl:**
Leprosy is a serious infectious disease caused by Mycobacterium leprae and Mycobacterium lepromatosis. Treatment involves a combination of antibiotics, targeting the bacterium and preventing its spread within the body. Corticosteroids might be used for nerve pain relief but are not the primary treatment modality for leprosy.