What are the characteristic clinical and laboratory findings in eosinophilic granulomatosis with polyangiitis (EGPA)?

Characteristic Findings in EGPA

EGPA presents with a triad of adult-onset asthma (>90% of patients), marked eosinophilia (>10% or >1,500 cells/μl), and multi-organ vasculitic involvement, with the clinical phenotype varying significantly based on ANCA status. 1

Core Clinical Features

Universal Manifestations

• Asthma: Present in >90% of patients, typically adult-onset, non-seasonal, progressive over time 1
• Eosinophilia: Nearly universal finding (>10% or >1,500 cells/μl absolute count), though can be masked by systemic glucocorticoids 1
• ENT involvement: Chronic rhinosinusitis with nasal polyps (60-80% of patients), recurrent even after surgical excision, plus otitis media 1

Common Organ Manifestations

Peripheral Neuropathy (50-70%):

• Mononeuritis multiplex pattern
• Predominantly sensory but may include motor deficits
• Axonal damage pattern on nerve conduction studies 1

Pulmonary Infiltrates (40-50%):

• Multiple and migratory
• Ground-glass opacities on imaging
• Glucocorticoid-responsive 1

Skin Lesions (frequent):

• Heterogeneous presentation
• Palpable purpura is the most vasculitis-specific finding 1

Cardiac Involvement:

• Myocarditis and pericarditis
• More common in ANCA-negative patients
• Critical for prognosis 1

Other Manifestations:

• Gastrointestinal involvement
• Renal disease (proteinuria, hematuria, varying degrees of kidney failure)
• Constitutional symptoms: fatigue, weight loss, myalgia, arthralgia 1

Laboratory Findings

ANCA Status (Critical Distinguishing Feature)

ANCA-Positive (30-40% of patients) 1:

• Predominantly MPO-ANCA (P-ANCA pattern)
• Associated with vasculitic phenotype:
  • Glomerulonephritis
  • Peripheral neuropathy
  • Palpable purpura
  • More frequent relapses

ANCA-Negative (60-70% of patients):

• Associated with eosinophilic phenotype:
  • Cardiac involvement (myocarditis)
  • Lung infiltrates
  • Gastrointestinal manifestations
  • Worse overall survival (due to cardiac complications) 1

Important caveat: Rare PR3-ANCA-positive patients exist and present more like granulomatosis with polyangiitis (GPA) with lung nodules and less active asthma 1

Additional Laboratory Parameters

• Elevated inflammatory markers: ESR and CRP typically elevated 2
• Neutrophil-to-lymphocyte ratio: May be elevated (median 2.29 in recent cohorts) 2
• ANA positivity: Detected in approximately 50% of patients, may correlate with higher disease activity 2

Histopathological Findings

The classic triad (though rarely all present simultaneously) 1:

1. Eosinophilic tissue infiltration
2. Necrotizing vasculitis
3. Extravascular granulomas

Critical point: Histopathological evidence of vasculitis is more common in ANCA-positive patients, though lesions typically show mixed patterns making categorization challenging 1

Diagnostic Approach

There are no validated diagnostic criteria for EGPA 1. Diagnosis should be based on:

1. Highly suggestive clinical features (asthma + eosinophilia + organ involvement)
2. Objective evidence of vasculitis (ideally histopathology)
3. ANCA testing (supportive but not required)

Classification Criteria (Not for Diagnosis)

The 2022 ACR-EULAR criteria provide a framework (≥6 points suggests EGPA) 1:

• Eosinophil count ≥1 × 10⁹/L: +5 points
• Obstructive airway disease: +3 points
• Nasal polyps: +3 points
• Extravascular eosinophilic inflammation: +2 points
• Mononeuritis multiplex/motor neuropathy: +1 point
• C-ANCA/PR3-ANCA positivity: -3 points
• Hematuria: -1 point

Clinical Pitfalls

1. Glucocorticoid masking: Eosinophilia may be suppressed by steroid treatment, complicating diagnosis 1

2. Phase overlap: The classic three-phase evolution (allergic → eosinophilic → vasculitic) often overlaps or occurs out of sequence 1

3. ANCA interpretation: Isolated P-ANCA without MPO-ANCA can occur in non-vasculitic inflammatory conditions (e.g., inflammatory bowel disease) 1

4. Differential diagnosis challenges: Must distinguish from hypereosinophilic syndromes, other small-vessel vasculitides (especially GPA), parasitic infections, and IgG4-related disease 1

5. Cardiac involvement: Often subclinical initially but represents the major cause of mortality in ANCA-negative patients—requires proactive screening 1