c-ANCA is characteristic for –
**Core Concept**
c-ANCA (cytoplasmic antineutrophil cytoplasmic antibodies) is a type of autoantibody targeting proteinase 3 (PR3), a serine protease found in the azurophilic granules of neutrophils. This autoantibody is closely associated with granulomatosis with polyangiitis (GPA), a form of vasculitis affecting small vessels in various organs.
**Why the Correct Answer is Right**
The presence of c-ANCA is a hallmark of GPA, which typically involves the upper and lower respiratory tracts, kidneys, and sometimes the skin. The autoantibody reacts with the PR3 enzyme, leading to neutrophil activation and subsequent inflammation in affected tissues. This process results in the characteristic manifestations of GPA, such as pulmonary nodules, renal failure, and skin lesions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because c-ANCA is not typically associated with microscopic polyangiitis (MPA), which is usually characterized by p-ANCA (perinuclear antineutrophil cytoplasmic antibodies) positivity.
**Option B:** This option is incorrect because c-ANCA is not the primary autoantibody found in eosinophilic granulomatosis with polyangiitis (EGPA), previously known as Churg-Strauss syndrome. EGPA is more commonly associated with p-ANCA or MPO-ANCA.
**Option C:** This option is incorrect because c-ANCA is not a characteristic feature of systemic lupus erythematosus (SLE), which is a different autoimmune disease that can present with a wide range of autoantibodies.
**Clinical Pearl / High-Yield Fact**
When encountering a patient with symptoms suggestive of GPA, such as pulmonary nodules or renal failure, prompt testing for c-ANCA can aid in the diagnosis. A positive result can guide the initiation of immunosuppressive therapy to prevent further organ damage.
**Correct Answer:** C.