**Core Concept**
Leprosy reversal reaction, also known as Type 2 lepra reaction, is a clinical phenomenon where there is an increase in cell-mediated immunity against Mycobacterium leprae, leading to inflammation and worsening of pre-existing nerve damage. It is often seen in borderline lepromatous leprosy (BL) and borderline tuberculoid leprosy (BT) patients.

**Why the Correct Answer is Right**
The treatment of leprosy reversal reaction primarily involves corticosteroids to reduce inflammation and prevent nerve damage. However, the choice of corticosteroid is crucial, and prednisolone is often the preferred option due to its efficacy and safety profile. The use of prednisolone helps to reduce the production of pro-inflammatory cytokines and inhibit the activation of immune cells, thereby alleviating symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a corticosteroid, which is the primary treatment for leprosy reversal reaction.
**Option B:** This option is incorrect as thalidomide is not typically used as a first-line treatment for leprosy reversal reaction due to its potential side effects and teratogenicity.
**Option C:** This option is incorrect as cyclophosphamide is an immunosuppressive agent that is not typically used to treat leprosy reversal reaction.

**Clinical Pearl / High-Yield Fact**
It's essential to recognize that leprosy reversal reaction can be a medical emergency, and prompt treatment is necessary to prevent permanent nerve damage. Corticosteroids should be initiated as soon as possible, and the choice of corticosteroid should be based on the severity of symptoms and the patient's overall health status.

**Correct Answer:** D.