A 35-year-old Indian woman with a 2-year history of recurrent oral ulcers, genital ulcers, and ocular inflammation presents with acute thrombosis of the superior vena cava. Which single feature best distinguishes Behçet's Disease from Polyarteritis Nodosa (PAN)?

## Distinguishing Behçet's Disease from Polyarteritis Nodosa ### Core Discriminating Feature **Key Point:** Recurrent mucocutaneous ulceration (oral, genital, ocular) is the pathognomonic hallmark of Behçet's Disease and is absent in PAN. This is the single best clinical discriminator. ### Comparative Table | Feature | Behçet's Disease | Polyarteritis Nodosa (PAN) | | --- | --- | --- | | **Mucocutaneous ulcers** | Hallmark (oral, genital, ocular) — present in >95% | Absent | | **Vessels involved** | Small and medium vessels (veins and arteries) | Medium and small muscular arteries (sparing lungs, glomeruli) | | **Pathology** | Leukocytoclastic vasculitis, thrombophlebitis | Necrotizing vasculitis without immune complex deposition | | **Ocular involvement** | Uveitis (anterior and posterior), retinitis | Rare; not a feature | | **Genital ulcers** | Recurrent, painful, scarring | Absent | | **Thrombosis** | Common (SVP, DVT, arterial) | Rare | | **CNS involvement** | Neuro-Behçet's (meningoencephalitis, stroke) | Rare | | **Renal involvement** | Glomerulonephritis (IgA, proliferative) | Segmental infarction, no GN | | **HLA association** | HLA-B51 (especially in Mediterranean, Asian populations) | No HLA association | | **Diagnosis** | Pathergy test, clinical criteria (International Study Group) | Biopsy (medium artery necrotizing vasculitis) | ### Why Mucocutaneous Ulceration is Pathognomonic **High-Yield:** The **International Study Group diagnostic criteria for Behçet's Disease** require: 1. Recurrent oral ulcers (mandatory) 2. PLUS two of: recurrent genital ulcers, ocular lesions (uveitis), skin lesions, or positive pathergy test Recurrent mucocutaneous ulceration is **not a feature of PAN** and is virtually diagnostic of Behçet's when present with systemic vasculitis. **Clinical Pearl:** A patient with: - Recurrent oral + genital ulcers - Uveitis - Thrombosis (SVP, DVT) - Elevated ESR/CRP → **Behçet's Disease** (not PAN) A patient with: - Mononeuritis multiplex - Testicular pain - Renal infarction - NO mucocutaneous ulcers → **PAN** (not Behçet's) ### Why Other Features Do Not Discriminate - **Medium-sized artery involvement:** Both conditions involve medium arteries; PAN is *exclusively* medium artery disease, but Behçet's also involves medium vessels - **Systemic vasculitis:** Both are systemic; this is non-discriminatory - **Elevated inflammatory markers:** Both present with elevated ESR/CRP; not specific **Mnemonic:** **BEHÇET = Ulcers** (oral, genital, ocular). If you see recurrent mucocutaneous ulcers + vasculitis → think Behçet's first. **Tip:** In NEET PG, if a vasculitis question mentions recurrent oral AND genital ulcers, the answer is almost always Behçet's Disease, regardless of other features.