**Question:** In pauci immune glomerulonephritis, immunofluorescence of renal biopsy specimens do not reveal any evidence of immunoglobulin or complement deposition. Pauci immune necrotizing glomerulonephritis is seen in:

A. Systemic lupus erythematosus (SLE)
B. IgA nephropathy
C. Membranous nephropathy
D. Thrombotic thrombocytopenic purpura (TTP)

**Correct Answer:** C. Membranous nephropathy

**Core Concept:**
Pauci immune glomerulonephritis is a type of glomerulonephritis characterized by the absence of immunoglobulin and complement deposition in the renal biopsy specimens. Glomerulonephritis is a group of kidney disorders characterized by inflammation of the glomeruli, which are the tiny blood vessels found in the kidneys responsible for filtering blood.

**Why the Correct Answer is Right:**
In membranous nephropathy, there is deposition of immune complexes (mainly immunoglobulin G, IgG) on the glomerular basement membrane (GBM). This leads to a thickening of the GBM, which results in proteinuria, hematuria, hypertension, and sometimes renal failure. Membranous nephropathy is often associated with autoimmune diseases like systemic lupus erythematosus (SLE) and other autoimmune disorders (e.g., Giant cell arteritis). In pauci immune glomerulonephritis, there is minimal immune complex deposition, hence the term "pauci immune". This leads to minimal histological changes and less severe clinical manifestations.

**Why Each Wrong Option is Incorrect:**
A. Systemic lupus erythematosus (SLE) typically presents with more severe immune complex deposition and shows membranous nephropathy, not pauci immune glomerulonephritis.
B. IgA nephropathy is characterized by deposition of IgA immune complex in mesangium, not GBM. It is not a correct answer.
D. Thrombotic thrombocytopenic purpura (TTP) is a disorder caused by deficient ADAMTS13 activity, leading to unregulated von Willebrand factor multimers, platelet aggregation, and microangiopathic hemolytic anemia. It is not related to glomerulonephritis.

**Clinical Pearl:**
Membranous nephropathy is a common cause of nephrotic syndrome in adults and is associated with autoimmune disorders like SLE. In contrast, pauci immune glomerulonephritis is a rare entity with minimal immune complex deposition and milder clinical manifestations. Membranous nephropathy and pauci immune glomerulonephritis are two distinct entities, and their clinical presentations and histopathological findings are different. Membranous nephropathy is more common and presents with nephrotic syndrome, while pauci immune glomerulonephritis is rare and presents with milder clinical manifestations. Membranous nephropathy often has a positive antinuclear antibody (ANA) test, while pauci immune glomerul