**Question:** Which is associated with vasculitis of medium size vessels -

A. Rheumatoid Arthritis
B. Polyarteritis Nodosa
C. Granulomatosis with Polyangiitis (formerly known as Wegener's Granulomatosis)
D. Churg-Strauss Syndrome

**Correct Answer: B. Polyarteritis Nodosa**

**Core Concept**: Vasculitis is a group of clinical syndromes characterized by inflammation of blood vessels. Vasculitis can affect different sizes of blood vessels, including large, small, and medium vessels. Vasculitis of medium size vessels is primarily associated with specific autoimmune diseases.

**Why the Correct Answer is Right**: Polyarteritis Nodosa (PAN) is a systemic necrotizing vasculitis that primarily involves medium-sized arteries, particularly the muscular arteries, leading to inflammation and damage of the vessel walls. This condition is characterized by the involvement of multiple organ systems, causing a wide range of clinical manifestations.

**Why Each Wrong Option is Incorrect**:

A. Rheumatoid Arthritis (RA) primarily affects small joints and is an autoimmune disorder characterized by inflammation of the synovial membranes, not the vasculature. While RA can involve medium-sized vessels in rare cases, it is not the primary cause of vasculitis of medium-sized vessels.

B. Granulomatosis with Polyangiitis (GPA) and Churg-Strauss Syndrome (CSS) are both characterized by vasculitis affecting small and medium-sized vessels, not just medium-sized vessels.

C. Granulomatosis with Polyangiitis (GPA) and Churg-Strauss Syndrome (CSS) are classified as ANCA-associated vasculitides, which are autoimmune disorders with a characteristic presence of antineutrophil cytoplasmic antibodies (ANCA). They primarily affect small and medium-sized vessels, not just medium-sized vessels.

**Clinical Pearl**: Vasculitis can manifest in various clinical scenarios, and understanding the specific type of vasculitis is crucial for proper diagnosis and treatment. Adequate knowledge of these conditions will enable the physician to identify the correct diagnosis and initiate appropriate management strategies for patients with suspected vasculitis affecting medium-sized vessels.