A 35-year-old man with newly diagnosed tuberculosis develops SJS with involvement of oral mucosa, conjunctiva, and anogenital region. Which is the most common site of mucosal involvement in SJS/TEN?

Explanation

## Mucosal Involvement Pattern in SJS/TEN **Key Point:** The oral mucosa is the most frequently affected mucosal site in SJS/TEN, present in >90% of cases, often preceding cutaneous manifestations [cite:Harrison 21e Ch 56]. ### Frequency of Mucosal Involvement | Mucosal Site | Frequency | Clinical Significance | |---|---|---| | **Oral mucosa** | >90% | Severe erosions, difficulty eating/swallowing | | Conjunctiva | 50–80% | Pseudomembrane formation, symblepharon risk | | Anogenital region | 30–50% | Erosions, dysuria, secondary infection | | Respiratory tract | 10–25% | Laryngeal involvement → airway compromise | | Esophageal | 5–10% | Stricture formation (late complication) | **High-Yield:** Oral involvement is so characteristic that absence of oral ulceration should prompt reconsideration of the diagnosis. Severe oral erosions with pseudomembrane formation are a hallmark of SJS/TEN [cite:Robbins 10e Ch 25]. ### Clinical Presentation of Oral Involvement 1. **Early:** Erythema and edema of oral mucosa 2. **Acute:** Painful erosions, pseudomembranes, bleeding 3. **Sequelae:** Microstomia, ankyloglossia (rare), difficulty with oral intake ### Progression of Mucosal Involvement ```mermaid flowchart TD A[SJS/TEN Onset]:::outcome --> B[Oral mucosa involvement >90%]:::action B --> C{Severity?}:::decision C -->|Mild| D[Localized erosions]:::outcome C -->|Severe| E[Extensive pseudomembranes, bleeding]:::urgent E --> F[Nutritional support needed]:::action A --> G[Conjunctival involvement 50-80%]:::action A --> H[Anogenital involvement 30-50%]:::action G --> I[Risk of symblepharon]:::urgent ``` **Clinical Pearl:** The severity of oral involvement often correlates with overall disease severity and prognosis. Patients with extensive oral erosions require careful monitoring for secondary bacterial infection and nutritional support via nasogastric feeding if necessary. **Warning:** Respiratory tract involvement, though less common (10–25%), is a medical emergency. Laryngeal edema can lead to airway obstruction and requires immediate intervention (intubation, tracheostomy).