c-ANCA is positive in
**Core Concept**
c-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) is a type of autoantibody directed against certain enzymes in the cytoplasm of neutrophils, specifically proteinase 3 (PR3). This antibody is closely associated with the pathogenesis of granulomatosis with polyangiitis (GPA), a form of vasculitis.
**Why the Correct Answer is Right**
The presence of c-ANCA is a diagnostic clue for GPA, which is characterized by necrotizing granulomatous inflammation of small to medium-sized vessels. The autoantibody targets PR3, leading to activation of neutrophils and subsequent vascular damage. In GPA, c-ANCA is found in approximately 70-90% of patients, making it a valuable serological marker for diagnosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because c-ANCA is not typically associated with this condition. While other types of ANCA may be present, c-ANCA is not a hallmark of this disease.
**Option B:** This option is incorrect because c-ANCA is not typically associated with this condition. Microscopic polyangiitis (MPA) is more commonly associated with p-ANCA (perinuclear anti-neutrophil cytoplasmic antibodies).
**Option C:** This option is incorrect because c-ANCA is not typically associated with this condition. Eosinophilic granulomatosis with polyangiitis (EGPA) is more commonly associated with p-ANCA.
**Clinical Pearl / High-Yield Fact**
c-ANCA positivity in a patient with GPA suggests a higher likelihood of relapse and more severe disease. Serial monitoring of ANCA titers may help guide treatment decisions and predict disease activity.
**Correct Answer:** C. Granulomatosis with polyangiitis (GPA)