Classification Criteria for Polyarteritis Nodosa
The 1990 American College of Rheumatology (ACR) criteria remain the most widely used classification system for PAN, requiring 3 or more of 10 criteria for classification, though newer diagnostic approaches are emerging that may offer better performance. 1
The 1990 ACR Classification Criteria
The traditional ACR criteria include 10 items, with the presence of ≥3 criteria yielding 82.2% sensitivity and 86.6% specificity 1:
The 10 Criteria:
- Weight loss ≥4 kg
- Livedo reticularis
- Testicular pain or tenderness
- Myalgias
- Mononeuropathy or polyneuropathy
- Diastolic blood pressure >90 mm Hg
- Elevated BUN or creatinine
- Hepatitis B virus reactants in serum
- Arteriographic abnormality (aneurysms or occlusions of visceral arteries)
- Biopsy showing granulocyte or mixed leukocyte infiltrate in arterial wall
Important Limitations and Caveats
The 1990 ACR criteria have significant limitations in modern practice because they:
- Were developed before recognition of ANCA-associated vasculitis as a separate entity
- Do not account for microscopic polyangiitis (MPA), leading to misclassification
- Were designed for classification (research), not diagnosis (clinical practice)
- Show poor performance when distinguishing PAN from other vasculitides, particularly MPA 2
Alternative Diagnostic Approaches
French Vasculitis Study Group Criteria (2008)
A more discriminating approach uses 3 positive predictive parameters and 5 negative predictive parameters 2:
Positive predictors:
- Hepatitis B virus antigen/DNA in serum
- Arteriographic abnormalities
- Mononeuropathy or polyneuropathy
Negative predictors (argue against PAN):
- ANCA positivity
- Asthma
- Ear, nose, throat signs
- Glomerulopathy
- Cryoglobulinemia
This approach achieved 70.6% sensitivity and 92.3% specificity for all vasculitides, and 89.7% sensitivity and 83.1% specificity when distinguishing PAN from MPA specifically 2.
Provisional Seven-Item Criteria (2020-2021)
Recent Japanese studies developed simplified criteria with ≥4 of 7 items showing 92.3% sensitivity and 91.7% specificity 3, subsequently validated with 83.7% sensitivity and 96.8% specificity 4. These criteria outperformed both ACR and Japanese MHLW criteria in real-world diagnostic settings.
Modern Diagnostic Confirmation (Per 2021 ACR/VF Guidelines)
Diagnosis is confirmed by either tissue biopsy or angiography 5:
Histologic Findings:
- Mixed-cell inflammatory infiltrates in vessel wall
- Fibrinoid necrosis
- Absence of granulomas and giant cells (distinguishes from other vasculitides)
Angiographic Findings:
- Saccular or fusiform aneurysms
- Stenotic lesions in mesenteric, hepatic, and renal arteries
- Can use conventional catheter angiography (gold standard for resolution) or CT/MR angiography 5
Critical Exclusions
Before diagnosing idiopathic PAN, you must exclude:
- ANCA-associated vasculitis (check ANCA)
- Hepatitis B-associated PAN (separate entity with different treatment)
- DADA2 (Deficiency of Adenosine Deaminase 2) - especially in children and young adults presenting with PAN-like illness 6, 7
- Cutaneous-only PAN (managed differently from systemic PAN)
The absence of glomerulonephritis, ANCA positivity, and granulomas helps distinguish PAN from ANCA-associated vasculitis and granulomatous vasculitides 2.