How should eosinophilia be evaluated and managed in a patient with IgA vasculitis (Henoch‑Schönlein purpura)?

Eosinophilia in IgA Vasculitis: Evaluation and Management

Eosinophilia is NOT a typical feature of IgA vasculitis (Henoch-Schönlein purpura), and its presence should prompt immediate investigation for alternative diagnoses, particularly eosinophilic granulomatosis with polyangiitis (EGPA) or other eosinophilic disorders.

Key Diagnostic Distinction

IgA vasculitis does not characteristically present with eosinophilia. In fact, one study found elevated eosinophil cationic protein (ECP) in HSP patients, suggesting some eosinophil activation 1, but this represents immune activation rather than true eosinophilia as a disease feature. The presence of significant peripheral blood eosinophilia (>10% or >1,500 cells/μl) in a patient with suspected IgA vasculitis should raise red flags.

Critical Differential Diagnosis: EGPA

When eosinophilia is present alongside vasculitic features, EGPA must be ruled out. The 2022 ACR-EULAR criteria for EGPA include 2:

• Eosinophil count ≥1 × 10⁹/L (+5 points)
• Obstructive airway disease/asthma (+3 points)
• Nasal polyps (+3 points)
• Mononeuritis multiplex or motor neuropathy (+1 point)
• Extravascular eosinophilic inflammation on biopsy (+2 points)

A cumulative score ≥6 classifies small-vessel vasculitis as EGPA with 85% sensitivity and 99% specificity 2.

EGPA vs IgA Vasculitis: Key Distinguishing Features

Look for these specific clinical clues:

• Respiratory history: EGPA almost always presents with asthma (>90% of cases) and chronic rhinosinusitis with nasal polyps (60-80%) 2. IgA vasculitis does not.
• Age and presentation: IgA vasculitis predominantly affects children with benign course; EGPA affects adults (~50 years mean age) with more severe organ involvement 2, 3.
• Cardiac involvement: Myocarditis and pericarditis are common in EGPA, particularly in ANCA-negative patients 2. This is not typical of IgA vasculitis.
• Renal patterns: While both can cause glomerulonephritis, EGPA with MPO-ANCA positivity shows necrotizing glomerulonephritis, whereas IgA vasculitis shows IgA-dominant mesangial deposits 4.

Systematic Evaluation Algorithm

Step 1: Confirm True Eosinophilia

• Absolute eosinophil count >1,500 cells/μl or >10%
• Critical caveat: Glucocorticoids can mask eosinophilia 2. If the patient is already on steroids, eosinophilia may be suppressed.

Step 2: Assess for EGPA-Specific Features

Mandatory investigations 2:

• Pulmonary: Chest imaging for infiltrates (migratory, multiple), obstructive pattern on spirometry
• ENT: Evaluate for chronic rhinosinusitis, nasal polyps, sinus abnormalities
• Neurologic: Nerve conduction studies if peripheral neuropathy suspected (mononeuritis multiplex pattern with axonal damage)
• Cardiac: ECG, troponin, echocardiography (myocarditis/pericarditis more common in ANCA-negative EGPA)
• ANCA testing: MPO-ANCA by ELISA (30-40% of EGPA patients are positive) 2

Step 3: Rule Out Other Eosinophilic Disorders 5, 6

Secondary causes to exclude:

• Parasitic infections (stool ova and parasites, serology)
• Drug hypersensitivity reactions (medication review)
• Allergic conditions (allergic bronchopulmonary aspergillosis)
• Hematologic disorders: Peripheral smear, flow cytometry, consider bone marrow biopsy if atypical features
• FIP1L1-PDGFRA fusion gene testing for myeloproliferative hypereosinophilic syndrome

Step 4: Tissue Diagnosis When Feasible

Biopsy targets 2:

• Skin: Look for necrotizing vasculitis with extravascular eosinophils (EGPA) vs leukocytoclastic vasculitis with IgA deposits (IgA vasculitis)
• Nerve/muscle: If neuropathy present
• Kidney: If significant renal involvement to distinguish patterns

Direct immunofluorescence (DIF): IgA vasculitis shows IgA deposits; EGPA shows no immune deposits 7. However, negative DIF does not exclude IgA vasculitis 7.

Management Implications

If EGPA is confirmed rather than IgA vasculitis:

• Severity stratification is essential 2
• Organ-threatening disease: Cyclophosphamide plus high-dose glucocorticoids for remission induction 8
• Non-organ threatening: Methotrexate plus glucocorticoids 8
• Refractory disease: Consider rituximab, mepolizumab (anti-IL-5), or other biologics 8, 2
• Maintenance: Azathioprine, leflunomide, or methotrexate with low-dose glucocorticoids 8

If IgA vasculitis is confirmed despite eosinophilia:

• The eosinophilia likely represents a secondary phenomenon or concurrent condition
• Treat IgA vasculitis according to severity: supportive care for mild disease, corticosteroids for severe GI or renal involvement 3, 9, 10
• Address the eosinophilia based on identified underlying cause

Critical Pitfalls to Avoid

1. Do not assume eosinophilia is part of IgA vasculitis - it is not a recognized feature and demands alternative explanation
2. Do not delay ANCA testing - MPO-ANCA positivity strongly suggests EGPA over IgA vasculitis 2
3. Do not overlook cardiac evaluation - cardiac involvement in EGPA carries significant mortality risk and requires urgent assessment 2
4. Do not rely solely on DIF negativity to exclude IgA vasculitis, but use it to support EGPA (which lacks immune deposits) 7
5. Do not miss the asthma history - virtually all EGPA patients have asthma; its absence makes EGPA unlikely 2