You’re cruising through a pulmonary q-bank and suddenly the stem hits you with asthma + eosinophilia + neuropathy. You know it’s pointing somewhere… but the answer choices are all “vasculitis-ish” and start to blur together. This is exactly where Step-style questions reward pattern recognition and punish sloppy differentiating. Let’s break down Eosinophilic granulomatosis with polyangiitis (EGPA, aka Churg–Strauss) and then dissect the distractors like you’d do on test day.
The Vignette (Classic Board Style)
A 42-year-old woman with a long history of asthma and chronic sinus congestion presents with worsening shortness of breath, fever, and weight loss. She has numbness and tingling in her right foot and left hand. Exam shows wheezing and a mild purpuric rash on the lower extremities. Labs show marked eosinophilia and elevated IgE. Chest imaging demonstrates patchy, transient pulmonary infiltrates.
Question: What is the most likely diagnosis?
Correct Answer: Eosinophilic Granulomatosis with Polyangiitis (EGPA)
Why it’s EGPA
EGPA is a small-to-medium vessel necrotizing vasculitis characterized by:
- Asthma (often severe, adult-onset, hard to control)
- Allergic rhinitis / chronic sinusitis (ENT involvement is common)
- Peripheral eosinophilia and tissue eosinophilic inflammation
- Pulmonary infiltrates (often migratory/transient)
- Neuropathy, classically mononeuritis multiplex (think foot drop, wrist drop, asymmetric sensory/motor deficits)
- Palpable purpura or other skin findings from small-vessel vasculitis
Key immunology association (Step-relevant)
- p-ANCA / MPO-ANCA may be positive, but not always.
- If the question includes p-ANCA, it supports EGPA.
- If it’s ANCA-negative, EGPA is still very much in play if the clinical picture fits.
Pathology buzzwords
- Eosinophil-rich necrotizing granulomas
- Necrotizing vasculitis with eosinophilic infiltration
High-yield organ involvement
| Organ system | High-yield manifestation |
|---|---|
| Lung | Asthma, wheeze, transient infiltrates |
| ENT | Chronic sinusitis, nasal polyps |
| Nerves | Mononeuritis multiplex |
| Skin | Palpable purpura, nodules |
| Heart | Myocarditis (major cause of mortality in EGPA) |
| Kidney | Can occur, but often less dominant than in GPA/MPA |
How EGPA Fits Under “Pulmonary > Restrictive & Interstitial”
Even though EGPA screams “asthma” (obstructive), q-banks often slot it into interstitial/restrictive frameworks because the lung findings frequently present as:
- Patchy parenchymal infiltrates
- Eosinophilic pneumonia patterns
- Inflammatory lung disease that can mimic interstitial processes
So the “restrictive/interstitial” angle is really about parenchymal infiltrates and eosinophilic lung disease, not classic fibrotic ILD.
The Step 1/2 “Tell” Features (Memorize These)
The triad you should reflexively link to EGPA
- Asthma
- Eosinophilia
- Systemic vasculitis (neuropathy + skin + constitutional symptoms)
Common exam phrasing
- “Adult-onset asthma that worsened recently”
- “Migratory infiltrates”
- “Mononeuritis multiplex”
- “Elevated IgE”
- “p-ANCA (MPO) positivity”
Management (High Yield, Not Overkill)
- Systemic glucocorticoids are first-line for most.
- Add immunosuppressants for severe disease/organ-threatening involvement:
- Cyclophosphamide, azathioprine, methotrexate (depending on severity/phase)
- Biologics like mepolizumab (anti–IL-5) can be used in EGPA (especially eosinophilic/asthma-driven disease).
Clinical pearl: In EGPA, cardiac involvement (myocarditis) is a big prognostic factor—if the vignette hints at chest pain, arrhythmia, or heart failure symptoms, take it seriously.
Now, Why Every Distractor Is Wrong (and How They Try to Trick You)
Below are the common answer choices that show up alongside EGPA. The goal is to build a mental “anti-pattern” so you don’t get baited.
Distractor 1: Granulomatosis with Polyangiitis (GPA, Wegener)
Why it seems tempting: It’s a small-vessel vasculitis with pulmonary involvement and ENT symptoms.
Why it’s wrong here:
- GPA classically has:
- Upper + lower respiratory tract disease with necrotizing granulomas
- Hematuria/RBC casts from rapidly progressive GN
- c-ANCA (PR3-ANCA) association
- The vignette is dominated by:
- Asthma (not typical for GPA)
- Eosinophilia (points away from GPA)
- Neuropathy with eosinophils (points to EGPA)
One-liner:
GPA = c-ANCA + cavitary lung lesions + chronic sinusitis + GN, not asthma/eosinophilia.
Distractor 2: Microscopic Polyangiitis (MPA)
Why it seems tempting: Another small-vessel vasculitis, also p-ANCA-associated, can cause lung disease.
Why it’s wrong here:
- MPA typically causes:
- Pulmonary capillaritis → hemoptysis
- Rapidly progressive glomerulonephritis
- p-ANCA (MPO)
- But MPA does not feature:
- Asthma
- Granulomas
- Prominent eosinophilia
One-liner:
MPA = p-ANCA + hemoptysis + GN, but no asthma and no eosinophil-driven story.
Distractor 3: Polyarteritis Nodosa (PAN)
Why it seems tempting: Medium-vessel vasculitis with systemic symptoms and neuropathy.
Why it’s wrong here:
- PAN is associated with:
- HBV
- Medium-vessel necrotizing inflammation
- Renal microaneurysms, HTN
- Mononeuritis multiplex, livedo reticularis
- Key “PAN rules”:
- Spared lungs (major differentiator)
- Not an asthma/eosinophilia disease
One-liner:
PAN = systemic + neuropathy + renal/GI, but classically spares the lungs → not your wheezing/infiltrates case.
Distractor 4: Allergic Bronchopulmonary Aspergillosis (ABPA)
Why it seems tempting: Asthma + eosinophilia + elevated IgE is very ABPA-ish.
Why it’s wrong here: ABPA is hypersensitivity to Aspergillus in asthmatics/CF patients. It causes:
- Asthma exacerbations
- Eosinophilia
- Elevated IgE
- Central bronchiectasis
- Brown mucus plugs
- Positive Aspergillus-specific IgE/skin testing
But ABPA does not explain the systemic vasculitis clues:
- Mononeuritis multiplex
- Palpable purpura (vasculitic rash)
- Constitutional symptoms with multi-organ vasculitis pattern
Test-day separation:
- ABPA is “allergic airway + bronchiectasis”
- EGPA is “allergic airway + vasculitis”
One-liner:
ABPA = asthma + IgE + bronchiectasis; EGPA = asthma + eosinophilia + vasculitis/neuropathy.
Distractor 5: Hypereosinophilic Syndrome (HES)
Why it seems tempting: Marked eosinophilia + systemic symptoms can overlap.
Why it’s wrong here: HES is defined by persistent eosinophilia with end-organ damage but without a clear cause (e.g., parasites, allergy, vasculitis). It often features:
- Cardiac involvement (endomyocardial fibrosis, thrombosis)
- Thromboembolic complications
- Variable skin/lung symptoms
EGPA is more likely when you have:
- A strong asthma/sinusitis prodrome
- Vasculitic features (purpura, neuropathy)
- Migratory pulmonary infiltrates consistent with eosinophilic inflammation + vasculitis
One-liner:
HES is eosinophilia without a unifying allergic-asthma-to-vasculitis progression; EGPA has the asthma → eosinophilic inflammation → vasculitis arc.
Distractor 6: Idiopathic Pulmonary Fibrosis (IPF)
Why it seems tempting: If the question bank is tagged “restrictive/interstitial,” they may toss IPF in.
Why it’s wrong here: IPF presents with:
- Progressive dyspnea, dry cough
- Older age (usually >50)
- Velcro crackles, clubbing
- HRCT: subpleural basal reticulation + honeycombing
- No eosinophilia, no asthma, no neuropathy, no purpura
One-liner:
IPF is chronic fibrotic ILD—no eosinophils, no asthma, no systemic vasculitis.
Rapid-Fire Differentiation Table (Worth Memorizing)
| Condition | Key clue | ANCA | Lungs | Eosinophilia | Classic extra |
|---|---|---|---|---|---|
| EGPA | Asthma + eosinophilia + neuropathy | p-ANCA (sometimes) | Infiltrates, asthma | Yes | Mononeuritis multiplex, myocarditis |
| GPA | Sinus + lung + kidney | c-ANCA (PR3) | Nodules/cavitation | No | GN, saddle nose |
| MPA | Hemoptysis + GN | p-ANCA (MPO) | Capillaritis | No | No granulomas |
| PAN | Medium-vessel, HBV | ANCA– | Spared | No | Renal/GI ischemia, aneurysms |
| ABPA | Asthma + high IgE + bronchiectasis | — | Bronchiectasis | Yes | Brown plugs, Aspergillus IgE |
| IPF | Progressive fibrosis, honeycombing | — | Restrictive fibrotic ILD | No | Velcro crackles, clubbing |
Exam “Trap Alerts” (How They Try to Get You)
- p-ANCA is not exclusive to EGPA. MPA can also be p-ANCA+. You need the asthma + eosinophilia + granulomatous/eosinophilic tissue disease vibe.
- Asthma + eosinophilia alone could be ABPA. Add neuropathy/purpura/systemic vasculitis and it becomes EGPA.
- Pulmonary infiltrates in EGPA are often transient/migratory—that’s a huge clue.
Take-Home High-Yield Summary
- EGPA (Churg–Strauss) = asthma + eosinophilia + systemic small-vessel vasculitis
- Think mononeuritis multiplex, palpable purpura, migratory infiltrates, sinusitis, and sometimes p-ANCA (MPO).
- If the stem screams “allergic airway disease” but the question is really about a multisystem vasculitis, EGPA is the answer.