Characteristic Findings in EGPA
EGPA diagnosis should be suspected in patients presenting with the triad of asthma, eosinophilia, and end-organ involvement, particularly peripheral neuropathy, lung infiltrates, or cardiomyopathy 1.
Clinical Manifestations
Core Features (Present in Most Patients)
- Asthma: Present in 86.7% of patients, often late-onset and severe, with median duration of 45 months before diagnosis 2
- Chronic rhinosinusitis with nasal polyps: Occurs in 90% of patients 2
- Peripheral blood eosinophilia: >10% in 76.7% of cases 2
Organ-Specific Manifestations
Neurologic (33-50% of patients)
- Mononeuritis multiplex and motor neuropathy are characteristic findings 1
- Peripheral neuropathy is one of the most common vasculitic manifestations 1
Cardiac (26.7% of patients)
- Eosinophilic cardiomyopathy is a critical manifestation, more common in ANCA-negative patients 1
- Represents a poor prognostic factor requiring aggressive treatment 1
Cutaneous (43.3% of patients)
- Palpable purpura is the classic vasculitic skin manifestation 2
- Other skin lesions may include nodules and urticarial lesions 2
Pulmonary
- Migratory infiltrates on chest radiograph 2
- Ground-glass opacities (70% of cases) 2
- Nodular shadows and tree-in-bud pattern 3
Renal (10% of patients)
- Glomerulonephritis, though less common than in other ANCA-associated vasculitides 2
- More frequent in ANCA-positive patients 1
Gastrointestinal (10% of patients)
- Eosinophilic gastroenteritis 2
Laboratory Findings
Essential Tests
- Eosinophil count: Typically ≥1 × 10⁹/L (this finding scores +5 points in ACR-EULAR criteria) 1
- Total IgE: Frequently elevated >300 KU/L 3
- CRP: Often elevated >14.1 mg/L 3
- ESR: Median values around 24 mm/h at diagnosis 4
ANCA Testing
ANCA positivity occurs in only 30-40% of EGPA patients 1. When positive:
- Predominantly MPO-ANCA (perinuclear pattern) 1
- PR3-ANCA (cytoplasmic pattern) is rare and scores negatively in classification criteria 1
Critical distinction: ANCA-positive patients more frequently manifest vasculitic features (glomerulonephritis, neuropathy, purpura), while ANCA-negative patients more commonly present with cardiomyopathy and lung involvement 1.
Additional Laboratory Markers
- ANA positivity: Detected in approximately 50% of patients at diagnosis 4
- FeNO: May be elevated >100 ppb in patients with active asthma 3
- Neutrophil-to-lymphocyte ratio: Median 2.29 at diagnosis 4
Imaging Findings
Chest Imaging
- Ground-glass opacities (most common, 70%) 2
- Migratory pulmonary infiltrates 2
- Nodular shadows 3
- Tree-in-bud pattern 3
Cardiac Imaging
Required in all suspected cases to evaluate for eosinophilic cardiomyopathy, particularly in ANCA-negative patients 1.
Histopathologic Findings
Biopsy is recommended when feasible but not essential for diagnosis 1. The classic triad of histopathologic features includes:
- Tissue eosinophilia: Extravascular eosinophilic infiltration in alveolar, interstitial, and vascular tissues 3
- Necrotizing vasculitis: Affects small and medium vessels 1
- Eosinophil-rich granulomatous inflammation: Less commonly observed 2
Organ-Specific Histopathology
Kidney
- Crescentic necrotizing glomerulonephritis with eosinophilic infiltrates 1
- Granulomatous changes and eosinophil-rich necrotizing vasculitis of arterioles and arteries 1
- Atypical presentations with membranous nephropathy may occur, particularly in ANCA-negative patients 1
Skin
- Leukocytoclastic vasculitis in patients with palpable purpura 1
- Eosinophilic infiltration with perivascular inflammation 5
Lung and ENT
- Eosinophilic tissue infiltration 3
- Necrotizing vasculitis (less common) 2
- Extravascular granulomas (least common) 2
Diagnostic Approach
A multidisciplinary evaluation is mandatory 1. The diagnostic workup should systematically investigate:
Baseline Investigations for All Patients
- Complete blood count with differential (eosinophil count)
- ANCA testing (both MPO and PR3)
- Inflammatory markers (ESR, CRP)
- Total IgE
- Comprehensive metabolic panel with urinalysis
- Chest imaging
- Cardiac evaluation (ECG, echocardiography, troponin)
- Neurologic examination
Targeted Investigations Based on Clinical Suspicion
- Nerve conduction studies if neuropathy suspected
- Cardiac MRI if cardiomyopathy suspected
- Sinus CT if chronic rhinosinusitis present
- Tissue biopsy from accessible affected organs 1
Critical Pitfalls to Avoid
- Do not rely on ANCA positivity: 60-70% of EGPA patients are ANCA-negative 1
- Do not use classification criteria as diagnostic criteria: The 1990 ACR and 2022 ACR-EULAR criteria were developed to distinguish EGPA from other vasculitides, not to diagnose it 1
- Do not miss cardiac involvement: Eosinophilic cardiomyopathy is a life-threatening complication requiring immediate recognition, particularly in ANCA-negative patients 1
- Do not overlook the prodromal phase: Asthma and rhinosinusitis may precede vasculitic manifestations by months to years 1
- Do not assume all three histopathologic features must be present: The complete triad of eosinophilia, vasculitis, and granulomas is rarely seen in a single biopsy 2