**Core Concept**
The Lucio phenomenon is a rare, life-threatening complication of leprosy characterized by severe hemophagocytic syndrome, which can lead to multi-organ failure. This condition is caused by a severe immune response to the leprosy bacillus, resulting in the destruction of infected macrophages and the release of pro-inflammatory cytokines.

**Why the Correct Answer is Right**
Exchange transfusion is the primary treatment for the Lucio phenomenon because it involves the removal of infected and activated macrophages from the circulation, thereby reducing the severity of the immune response and preventing further organ damage. This procedure is particularly effective in patients who are at risk of developing multi-organ failure. The removal of infected macrophages also helps to reduce the levels of pro-inflammatory cytokines, which contribute to the pathogenesis of the Lucio phenomenon.

**Why Each Wrong Option is Incorrect**
**Option A:** Steroids are not effective in treating the Lucio phenomenon because they can actually worsen the condition by suppressing the immune response and allowing the leprosy bacillus to replicate further.
**Option B:** Lenalidomide is an immunomodulatory drug that is used to treat certain types of cancer and autoimmune diseases, but it is not effective in treating the Lucio phenomenon.
**Option C:** Clofazimine is an antimicrobial agent that is used to treat leprosy, but it is not effective in treating the Lucio phenomenon, which is a complication of leprosy rather than the disease itself.

**Clinical Pearl / High-Yield Fact**
The Lucio phenomenon is a medical emergency that requires prompt treatment to prevent multi-organ failure. Early recognition of the condition and prompt initiation of exchange transfusion can significantly improve outcomes and reduce mortality.

**✓ Correct Answer: D. Exchange transfusion**