## **Core Concept**
The patient's presentation and renal biopsy findings are indicative of an immune complex-mediated glomerulonephritis. This condition occurs when antibodies bind to antigens in the glomeruli, leading to inflammation and kidney damage. The granular pattern seen on immunofluorescence is characteristic of immune complex deposition.

## **Why the Correct Answer is Right**
The correct answer, **C. Systemic Lupus Erythematosus (SLE)**, is a classic cause of immune complex-mediated glomerulonephritis. SLE is an autoimmune disease that can affect multiple organs, including the kidneys, and is known for its immune complex deposition. The granular pattern on immunofluorescence is consistent with the immune complex deposition seen in SLE. The patient's symptoms of decreased urine output, leg edema, and facial swelling are also consistent with nephritic syndrome, which can be a presentation of SLE.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Post-streptococcal glomerulonephritis (PSGN) typically presents with a nephritic syndrome and is caused by immune complex deposition following a streptococcal infection. However, the immunofluorescence pattern in PSGN is usually described as "starry sky" or "speckled," and it is more commonly seen in children.
* **Option B:** Goodpasture's syndrome is an autoimmune disease that affects the lungs and kidneys, caused by antibodies against the glomerular basement membrane. It does not typically present with a granular pattern of immune complex deposition on immunofluorescence.
* **Option D:** Minimal change disease is a common cause of nephrotic syndrome, particularly in children, and is characterized by the loss of foot processes of podocytes on electron microscopy. It does not typically present with immune complex deposition on immunofluorescence.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that SLE can present with a wide range of renal manifestations, from mild proteinuria to severe nephritic syndrome. The presence of a granular pattern on immunofluorescence suggests immune complex-mediated glomerulonephritis, and SLE should be considered in the differential diagnosis.

## **Correct Answer:** C. Systemic Lupus Erythematosus (SLE)