ANCA is positive in
**Core Concept**
Infectious and inflammatory diseases of the kidneys can be associated with the presence of antineutrophil cytoplasmic antibodies (ANCA). ANCA are a group of autoantibodies directed against various cytoplasmic components of neutrophils, and their presence is often used as a diagnostic marker for certain conditions.
**Why the Correct Answer is Right**
The correct answer is associated with Granulomatosis with Polyangiitis (GPA), formerly known as Wegener's granulomatosis. GPA is a systemic vasculitis characterized by the presence of ANCA, particularly c-ANCA (cytoplasmic ANCA) directed against proteinase 3 (PR3). The presence of ANCA in GPA is thought to play a role in the pathogenesis of the disease, contributing to the activation and damage of neutrophils.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the specific disease associated with ANCA positivity is not mentioned. While some diseases may have a higher prevalence of ANCA positivity, they are not as strongly associated with ANCA as GPA.
* **Option B:** This option is incorrect because the disease discussed is not typically associated with ANCA positivity. While some forms of vasculitis may have a higher prevalence of ANCA positivity, they are not as strongly associated with ANCA as GPA.
* **Option C:** This option is incorrect because the disease discussed is not typically associated with ANCA positivity. While some forms of vasculitis may have a higher prevalence of ANCA positivity, they are not as strongly associated with ANCA as GPA.
**Clinical Pearl / High-Yield Fact**
It is essential to note that ANCA positivity is not exclusive to GPA and can be found in other conditions, such as Microscopic Polyangiitis (MPA) and Eosinophilic Granulomatosis with Polyangiitis (EGPA). However, the presence of c-ANCA (PR3-ANCA) is highly suggestive of GPA.
**Correct Answer:** C.