The correct answer is b) Positive ANCA is characteristic in cases of renal involvement
Based on the most recent and highest quality evidence, ANCA positivity is strongly associated with renal involvement in Churg-Strauss syndrome (now called eosinophilic granulomatosis with polyangiitis, EGPA) 1.
Analysis of Each Statement:
a) CNS is typically affected - INCORRECT
The central nervous system is rarely affected in EGPA 1. While CNS involvement can occur (reported in 4-17% of cases across different cohorts), it is not a typical feature 1. The disease predominantly affects peripheral nerves, not the CNS 1.
b) Positive ANCA is characteristic in cases with renal involvement - CORRECT
This is the correct answer. The 2013 Chapel Hill Consensus Conference specifically incorporated the concept that ANCA positivity is associated with renal involvement in EGPA 1. Multiple high-quality studies confirm this association:
- MPO-ANCA positivity is strongly associated with glomerulonephritis 1
- ANCA-positive patients have a 5-fold higher risk of renal involvement (OR 5.097) compared to ANCA-negative patients 2
- Renal disease occurs in 27-51% of ANCA-positive patients versus only 12-16% of ANCA-negative patients 1, 3, 4
- ANCA positivity correlates with biopsy-proven vasculitis and necrotizing glomerulonephritis 3, 4
c) Peripheral neuropathy presents with stocking-glove distribution - INCORRECT
This is a critical pitfall to avoid. Peripheral neuropathy in EGPA presents as mononeuritis multiplex, NOT stocking-glove distribution 1. The pattern is:
- Mononeuritis multiplex (asymmetric, multifocal nerve involvement)
- Usually sensory but may cause motor deficits
- Axonal damage pattern on nerve conduction studies
- Occurs in 50-70% of patients 1
The stocking-glove pattern suggests a length-dependent polyneuropathy, which is not characteristic of EGPA vasculitis.
d) Peripheral blood eosinophilia is 5% - INCORRECT
This dramatically understates the eosinophilia in EGPA. Eosinophilia >10% or >1,500 cells/μL is observed in almost all patients 1. The 1990 ACR criteria specify eosinophilia >10% 1, and the 2022 ACR-EULAR criteria use a threshold of ≥1 × 10⁹/L 1. Eosinophilia of only 5% would be insufficient for diagnosis.
Key Clinical Pearls:
ANCA-positive versus ANCA-negative phenotypes differ significantly:
- ANCA-positive (30-40% of patients): Higher risk of renal involvement, peripheral neuropathy, purpura, and biopsy-proven vasculitis 1, 2
- ANCA-negative: More frequent cardiac involvement, pulmonary infiltrates, and generally worse overall survival 1, 2
Common pitfall: Don't confuse the peripheral neuropathy pattern in EGPA (mononeuritis multiplex) with diabetic or other metabolic neuropathies (stocking-glove distribution).