**Question:** A patient presents with respiratory symptoms i.e. a cough, hemoptysis and glomerulonephritis. His C-ANCA levels in serum were found to be raised. The most likely diagnosis is -

A. Pulmonary Vasculitis
B. Systemic Lupus Erythematosus
C. Systemic Sclerosis
D. Rheumatoid Arthritis

**Correct Answer:**

**Core Concept:**

C-ANCA (anti-neutrophil cytoplasmic antibodies) are a type of autoantibody that can be detected in the blood when a patient has a certain type of vasculitis called "Pulmonary Vasculitis". Vasculitis is an inflammation of the blood vessels, and pulmonary vasculitis specifically affects the blood vessels in the lungs. C-ANCA is a specific marker for a type of pulmonary vasculitis called "Wegener's Granulomatosis".

**Why the Correct Answer is Right:**

In this case, the patient presents with respiratory symptoms (cough, hemoptysis, and glomerulonephritis), which are typical signs of Wegener's Granulomatosis. Additionally, elevated C-ANCA levels in the serum support the diagnosis. Pulmonary Vasculitis is the most likely diagnosis due to the patient's symptoms and lab results.

**Why Each Wrong Option is Incorrect:**

A. Systemic Lupus Erythematosus (SLE) is a different autoimmune disorder characterized by inflammation of various organs, not specifically affecting the lungs. The presence of C-ANCA would not be expected in SLE.

B. Systemic Sclerosis (SSc) is a connective tissue disorder causing fibrosis and hardening of the skin and internal organs. It does not involve the lungs in the same way as Wegener's Granulomatosis.

C. Rheumatoid Arthritis (RA) is an autoimmune disorder affecting the joints, not the lungs. C-ANCA levels would not be elevated in RA.

**Clinical Pearl:**

C-ANCA testing is crucial in diagnosing Wegener's Granulomatosis and other vasculitides, as it helps distinguish between these disorders and connective tissue diseases or other autoimmune conditions. A positive C-ANCA test strongly suggests Wegener's Granulomatosis, so physicians should consider this diagnosis in patients presenting with respiratory symptoms and kidney involvement.