**Core Concept**
Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by *Mycobacterium leprae*. The disease primarily affects the skin, peripheral nerves, and mucous membranes, but it can also involve other organs, including the kidneys. Renal involvement in leprosy is relatively rare but can manifest in various forms, including glomerulonephritis.

**Why the Correct Answer is Right**
The most common renal lesion seen in leprosy is a type of glomerulonephritis known as membranous nephropathy. This condition is characterized by the deposition of immune complexes and complement components on the glomerular basement membrane, leading to damage to the glomerular filtration barrier. The pathogenesis of leprosy-related glomerulonephritis is thought to involve the activation of the immune system, with the production of antibodies against *M. leprae* antigens. The resulting immune complex deposition and complement activation lead to the characteristic histopathological changes seen in membranous nephropathy.

**Why Each Wrong Option is Incorrect**
* **Option A:** While renal involvement in leprosy can manifest in various forms, the most common lesion is not interstitial nephritis, which is more commonly associated with drugs and other conditions.
* **Option B:** Tubulointerstitial nephritis is a type of kidney injury that can occur in leprosy, but it is not the most common renal lesion seen in this disease.
* **Option C:** Focal segmental glomerulosclerosis (FSGS) is a type of glomerular disease that can occur in various conditions, but it is not the most common renal lesion seen in leprosy.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that renal involvement in leprosy is relatively rare, and when it occurs, it can manifest in various forms, including membranous nephropathy. A high index of suspicion and careful evaluation are necessary to diagnose leprosy-related renal disease.

**Correct Answer: C. Focal segmental glomerulosclerosis is a less common renal lesion seen in Leprosy compared to membranous nephropathy.**