Granulomatosis with polyangiitis (GPA)—formerly Wegener’s—is one of those “looks-like-everything” diseases that USMLE loves because it connects pulm + ENT + kidneys with a single unifying diagnosis. If you can recognize the classic triad, know what c-ANCA (PR3-ANCA) actually means, and distinguish GPA from its closest mimics (Goodpasture, MPA, EGPA), you’ll pick up easy points on both Step 1 and Step 2.
Where GPA Fits in Pulmonary (and Why It Shows Up Under “Interstitial/Restrictive”)
Even though GPA is a small-to-medium vessel necrotizing vasculitis, it commonly presents with pulmonary parenchymal disease (nodules, cavitation, diffuse alveolar hemorrhage) that can clinically resemble “diffuse lung disease” and cause restrictive physiology in some cases—especially when there’s widespread inflammation/hemorrhage.
Big picture: think pulmonary-renal syndrome, plus upper airway involvement.
Definition (The One-Liner You Should Memorize)
Granulomatosis with polyangiitis (GPA) is a necrotizing granulomatous vasculitis of small-to-medium vessels classically involving:
- Upper respiratory tract (sinuses, nose, ears)
- Lower respiratory tract (lungs)
- Kidneys (rapidly progressive glomerulonephritis)
Pathophysiology: What’s Actually Happening?
Immune mechanism (high-yield)
- GPA is strongly associated with c-ANCA, most commonly directed against proteinase-3 (PR3) in neutrophil granules.
- These ANCAs can activate neutrophils → neutrophil adhesion to endothelium → vascular inflammation and necrosis.
What “necrotizing granulomatous vasculitis” implies
- Necrotizing: vessel wall destruction → hemorrhage, ischemia.
- Granulomatous: macrophage/giant cell response, especially in the respiratory tract.
- Small-to-medium vessels: capillaries/venules/arterioles/small arteries—explains multiorgan involvement.
Key pathology patterns you’ll be tested on
- Upper airway: chronic granulomatous inflammation → tissue destruction (e.g., septal perforation).
- Lung: necrotizing granulomas and/or diffuse alveolar hemorrhage.
- Kidney: crescentic (RPGN) that is typically pauci-immune on immunofluorescence.
Clinical Presentation: The Classic Triad + “Sneaky” Clues
Core triad (memorize this)
- ENT: chronic sinusitis, otitis media, nasal ulcers
- Lungs: cough, dyspnea, hemoptysis, pleuritic chest pain
- Kidneys: hematuria, proteinuria, RBC casts → rapidly progressive renal failure
High-yield ENT findings
- Chronic sinusitis that doesn’t respond to routine antibiotics
- Nasal/oral mucosal ulcers
- Saddle-nose deformity (from cartilage destruction)
High-yield pulmonary findings
- Hemoptysis (diffuse alveolar hemorrhage is a major Step trigger)
- Cavitary lung nodules on imaging (another classic clue)
- Shortness of breath, cough, fever, malaise, weight loss
Renal findings (often silent until advanced)
- RBC casts and rising creatinine
- Features of RPGN (rapid decline in renal function over days–weeks)
Other systemic clues
- Palpable purpura (vasculitis)
- Arthralgias/myalgias
- Mononeuritis multiplex (less emphasized than in some other vasculitides, but fair game)
Diagnosis: What Confirms It (and What Doesn’t)
Step approach (what the test wants you to do)
- Suspect clinically (ENT + lung + kidney pattern)
- Support with serology
- Confirm with biopsy when possible
Labs and serologies
- c-ANCA (PR3-ANCA): strongly associated and high-yield
- Important nuance: ANCA supports diagnosis but is not definitive alone.
- Inflammation: ↑ESR/CRP, normocytic anemia, leukocytosis may be present.
- Urinalysis: hematuria, proteinuria, RBC casts
Imaging
Chest X-ray/CT may show:
- Multiple nodules, often cavitating
- Patchy infiltrates
- Signs of alveolar hemorrhage (diffuse opacities)
Histology (favorite board-style descriptions)
- Necrotizing granulomatous inflammation in respiratory tract
- Necrotizing vasculitis
- Kidney biopsy: crescentic glomerulonephritis with pauci-immune IF
- “Pauci-immune” = little to no immune complex deposition on IF.
Treatment: Induction vs Maintenance (Think Like a Clinician)
Induction of remission (severe organ-threatening disease)
- High-dose glucocorticoids (often IV initially if severe)
- Plus one of:
- Rituximab (anti-CD20), or
- Cyclophosphamide
When it’s truly emergent: diffuse alveolar hemorrhage and/or rapidly progressive GN → treat aggressively and early.
Maintenance of remission
After induction:
- Azathioprine, methotrexate, or rituximab (depending on severity, renal function, and regimen)
Supportive care pearls (Step 2 flavor)
- Infection prophylaxis may be needed depending on immunosuppressive regimen (e.g., PJP prophylaxis with some protocols).
- Monitor for medication toxicities (see table below).
High-Yield Associations and “Do Not Confuse” Differentials
GPA vs similar diseases (exam favorite)
| Disease | Key Clues | Antibody | Lung Findings | Kidney IF |
|---|---|---|---|---|
| GPA | ENT + lung + kidney; cavitary nodules; granulomas | c-ANCA (PR3) | Nodules/cavitation, hemoptysis | Pauci-immune |
| Microscopic polyangiitis (MPA) | Pulmonary-renal syndrome without granulomas/ENT classically | p-ANCA (MPO) | Alveolar hemorrhage possible | Pauci-immune |
| EGPA (Churg-Strauss) | Asthma + eosinophilia + sinusitis, neuropathy | p-ANCA (MPO) sometimes | Transient infiltrates | Variable |
| Goodpasture | Hemoptysis + hematuria; no sinus disease | Anti-GBM | Alveolar hemorrhage | Linear IF (IgG/C3) |
Board tip:
If you see sinusitis + cavitary lung lesions + hematuria, your default should be GPA until proven otherwise.
Classic Vignette Templates (What It “Looks Like” on USMLE)
Vignette 1: ENT + lungs
- Young/middle-aged adult with chronic sinusitis, epistaxis, cough, and hemoptysis
- CT shows multiple cavitary nodules
- Labs show c-ANCA positive
Vignette 2: Pulmonary-renal syndrome
- Hemoptysis + dyspnea + anemia (alveolar hemorrhage)
- UA with RBC casts, rising creatinine
- Biopsy: crescentic GN, pauci-immune
First Aid–Style Cross-References (What to Link in Your Head)
Use these as mental cross-links to your First Aid sections (wording varies by edition, but the concepts are consistent):
-
Vasculitides:
- GPA = necrotizing granulomatous vasculitis + c-ANCA (PR3)
- Contrast with MPA (p-ANCA) and EGPA (asthma/eosinophils)
-
Renal—RPGN:
- GPA causes pauci-immune crescentic glomerulonephritis
- Contrast with anti-GBM (Goodpasture) = linear IF
-
Pulmonary—hemoptysis/diffuse alveolar hemorrhage:
- GPA/MPA/Goodpasture are your main “pulmonary hemorrhage + kidney” bucket
- ENT involvement pushes you toward GPA
Medication Toxicity Mini-Table (Quick Step 2 Add-On)
| Drug | Why Used | High-Yield Toxicities |
|---|---|---|
| Glucocorticoids | Rapid anti-inflammatory for induction | Hyperglycemia, osteoporosis, infection risk, psych changes |
| Cyclophosphamide | Induction (severe disease) | Hemorrhagic cystitis, infertility, malignancy risk (also myelosuppression) |
| Rituximab | Induction/maintenance alternative | Infusion reactions, infections, HBV reactivation |
| Methotrexate | Maintenance (non-severe, adequate renal function) | Hepatotoxicity, marrow suppression, teratogenic |
| Azathioprine | Maintenance | Myelosuppression (TPMT-related), hepatotoxicity |
Ultra–High-Yield Takeaways (If You Only Memorize 6 Things)
- ENT + lung + kidney = think GPA.
- c-ANCA (PR3) is the classic association.
- Cavitary pulmonary nodules are a major imaging clue.
- Renal disease is RPGN with pauci-immune immunofluorescence.
- Confirm with biopsy showing necrotizing granulomatous vasculitis (when feasible).
- Treat severe disease with high-dose steroids + rituximab or cyclophosphamide, then transition to maintenance therapy.