A 28-year-old Indian man with a history of recurrent oral ulcers and genital ulcers presents with acute onset of floaters, photopsia, and blurred vision in both eyes. On examination, visual acuity is 6/36 bilaterally. Slit-lamp shows mild anterior chamber cells (1+) in both eyes. Fundoscopy reveals extensive hemorrhagic retinitis with retinal necrosis, branch retinal artery occlusion, and minimal vitritis. Anterior chamber reaction is disproportionately mild compared to posterior involvement. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Behçet's Disease with Posterior Uveitis ### Diagnostic Criteria and Clinical Presentation **Key Point:** Behçet's disease is a chronic, relapsing systemic vasculitis characterized by the triad of oral ulcers, genital ulcers, and ocular involvement. The ocular manifestation is typically a posterior uveitis with retinal vasculitis. ### Behçet's Disease: Diagnostic Criteria (International Study Group) | Criterion | Definition | | --- | --- | | **Recurrent oral ulcers** | Mandatory; minor, major, or herpetiform; ≥3 episodes in 12 months | | **Recurrent genital ulcers** | Scarring or not; observed by physician or patient | | **Eye lesions** | Anterior uveitis, posterior uveitis, or retinal vasculitis | | **Skin lesions** | Erythema nodosum, pseudofolliculitis, papulopustular lesions, acneiform lesions | | **Positive pathergy test** | Papule ≥2 mm at 24–48 hours after needle prick | **Diagnosis:** Recurrent oral ulcers + recurrent genital ulcers + eye involvement = Behçet's disease (meets criteria). ### Ocular Manifestations of Behçet's Disease ```mermaid flowchart TD A[Behçet's Disease]:::outcome --> B[Ocular Involvement<br/>50-70% of patients]:::outcome B --> C[Anterior Uveitis]:::action B --> D[Posterior Uveitis<br/>Most common & severe]:::action B --> E[Intermediate Uveitis]:::action D --> F[Retinal vasculitis<br/>Arteries & veins]:::outcome D --> G[Hemorrhagic retinitis<br/>Retinal necrosis]:::outcome D --> H[Branch retinal artery<br/>occlusion BRAO]:::outcome D --> I[Minimal vitritis<br/>disproportionate to<br/>posterior involvement]:::outcome ``` ### Key Distinguishing Features in This Case **High-Yield:** The hallmark of Behçet's posterior uveitis is **disproportionate posterior involvement with minimal anterior chamber reaction** — the opposite of most other posterior uveitis causes. | Feature | Behçet's | ARN (VZV) | CMV | Toxo | | --- | --- | --- | --- | --- | | **Anterior chamber cells** | Mild (1–2+) | Moderate to severe | Absent/minimal | Absent | | **Posterior involvement** | Severe vasculitis, hemorrhage | Peripheral retinal necrosis | Hemorrhagic retinitis | Focal reactivation | | **Vitritis** | Minimal/mild | Moderate to severe | Minimal | Mild | | **Systemic features** | Oral/genital ulcers, skin lesions | Dermatomal pain, CSF pleocytosis | Immunocompromised | Immunocompromised or reactivation | | **Bilateral involvement** | Common | Unilateral (initially) | Often bilateral | Unilateral | | **Retinal vasculitis** | Yes (hallmark) | No | No | No | | **Branch artery occlusion** | Yes | No | No | No | **Clinical Pearl:** Behçet's disease causes a **vasculitis** affecting both retinal arteries and veins, leading to branch retinal artery occlusion (BRAO), hemorrhagic retinitis, and necrosis. The minimal vitritis despite extensive posterior involvement is pathognomonic. ### Why Anterior Chamber Reaction Is Disproportionately Mild Behçet's posterior uveitis is primarily a **retinal vasculitis** (inflammation of retinal blood vessels), not a true uveal inflammation. The anterior chamber reaction reflects spillover from posterior inflammation, not primary anterior uveal involvement. This contrasts with: - **ARN:** severe anterior chamber reaction + posterior necrosis - **CMV:** minimal anterior chamber reaction but in immunocompromised hosts - **Toxo:** focal reactivation without systemic features ### Management Principles 1. **Confirm diagnosis:** Pathergy test (if available), HLA-B51 (supportive, not diagnostic) 2. **Systemic immunosuppression:** Corticosteroids + azathioprine or mycophenolate mofetil (not topical therapy alone) 3. **Anti-TNF therapy:** Infliximab for severe/refractory cases 4. **Monitor:** Repeated fundoscopy for progression, visual field defects, optic atrophy **Mnemonic: BEHÇET Posterior Uveitis Features — HARVEST** - **H**emorrhagic retinitis - **A**rteries & veins involved (vasculitis) - **R**etinal necrosis - **V**asculitis (hallmark) - **E**xtensive posterior involvement - **S**evere but minimal anterior chamber reaction - **T**riple feature: oral ulcers + genital ulcers + eye [cite:Kanski's Clinical Ophthalmology 9e Ch 10; Harrison 21e Ch 380]