## Diagnosis: Stevens-Johnson Syndrome (SJS) ### Histopathological Confirmation **Key Point:** The biopsy findings are diagnostic: - **Full-thickness epidermal necrosis** — hallmark of SJS/TEN - **Subepidermal blister formation** — due to epidermal-dermal separation - **Scattered apoptotic keratinocytes** — reflects TNF-α and Fas-mediated apoptosis - **Minimal dermal inflammation** — distinguishes SJS/TEN from erythema multiforme (which shows dense dermal infiltrate) This patient has **SJS** (not TEN) because the rash involves <10% BSA, but the pathology is identical to TEN—just less extensive. ### Clinical Context: Why TMP-SMX in an HIV Patient? **High-Yield:** Patients with advanced HIV (CD4 <200 cells/μL) are at **markedly increased risk** of SJS/TEN from TMP-SMX: - Impaired immune tolerance and altered drug metabolism - Slower acetylation of drug metabolites - Increased formation of reactive metabolites (arylamine) - TMP-SMX is the **most common cause of SJS/TEN in HIV-positive patients** ### Differential Diagnosis Table | Feature | SJS | DRESS | Acute HIV Exanthem | EM Major | | --- | --- | --- | --- | --- | | **Onset** | 1–3 weeks post-drug | 2–8 weeks post-drug | Days to weeks | Variable | | **Mucosal involvement** | Yes (>90%) | Rare | Rare | Yes | | **Target lesions** | True targets (3 zones) | Absent | Absent | True targets | | **Histology** | Full-thickness epidermal necrosis | Perivascular infiltrate, eosinophils | Superficial perivascular infiltrate | Dermal infiltrate, minimal epidermal necrosis | | **Systemic symptoms** | Fever, malaise | Fever, lymphadenopathy, hepatosplenomegaly | Fever, lymphadenopathy | Usually absent | | **Eosinophilia** | Absent or mild | **Present (>1,500/μL)** | Absent | Absent | | **Liver involvement** | Rare | Common (hepatitis) | Rare | Absent | | **Management** | Drug withdrawal, supportive care ± IVIG | Drug withdrawal, systemic corticosteroids | Supportive care | Topical/systemic corticosteroids | ### Management Algorithm for SJS ```mermaid flowchart TD A[SJS confirmed by biopsy]:::outcome --> B[Discontinue offending drug<br/>TMP-SMX]:::urgent B --> C{BSA involved<br/>and severity?}:::decision C -->|<10% BSA, stable vitals| D[High-dependency unit<br/>or ICU admission]:::action C -->|≥10% BSA| E[ICU admission<br/>Burn unit consultation]:::action D --> F[Fluid/electrolyte management<br/>Nutritional support<br/>Infection prevention]:::action E --> F F --> G{Consider adjunctive<br/>therapy?}:::decision G -->|Early presentation| H[IVIG 2 g/kg over 3-5 days<br/>OR Systemic corticosteroids]:::action G -->|Late presentation| I[Supportive care alone<br/>Monitor for complications]:::action H --> J[Ophthalmology consult<br/>Monitor for blindness]:::action I --> J ``` ### Immediate Management Steps 1. **Discontinue TMP-SMX immediately** — no exceptions 2. **Admit to ICU or high-dependency unit** — even with <10% BSA, SJS requires close monitoring 3. **Fluid resuscitation** — use Parkland formula: 4 mL × %BSA × weight (kg) over first 24 hours 4. **Ophthalmology consultation** — conjunctival involvement can lead to symblepharon and blindness if not managed urgently 5. **Nutritional support** — enteral feeding preferred; avoid unnecessary antibiotics 6. **Consider IVIG** — 2 g/kg IV over 3–5 days if within 48 hours of rash onset; may halt disease progression 7. **Alternative PCP prophylaxis** — once stable, switch to dapsone or atovaquone-proguanil (avoid sulfonamides permanently) ### Why NOT DRESS? **Warning:** DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms) is a common distractor: - DRESS typically presents 2–8 weeks after drug initiation; this patient developed rash at 10 days (earlier) - DRESS features hepatosplenomegaly, lymphadenopathy, and **eosinophilia >1,500/μL** — not mentioned here - DRESS histology shows perivascular infiltrate with eosinophils, NOT full-thickness epidermal necrosis - DRESS is managed with drug withdrawal + systemic corticosteroids; SJS requires drug withdrawal + supportive care ± IVIG ### Why NOT Acute HIV Exanthem? **Clinical Pearl:** Acute HIV exanthem (part of acute retroviral syndrome) is a maculopapular rash without mucosal involvement, target lesions, or systemic toxicity. Histology shows superficial perivascular infiltrate, not epidermal necrosis. This patient's presentation is far too severe. ### Why NOT Erythema Multiforme Major? **Key Point:** EM major and SJS are **distinct entities** despite superficial overlap: - **EM major:** Typically triggered by HSV recurrence (not drugs); lesions are true targets with 3 zones; histology shows **dermal infiltrate with minimal epidermal necrosis**; mucosal involvement is present but less severe - **SJS:** Drug-triggered; full-thickness epidermal necrosis on biopsy; severe mucosal involvement; systemic toxicity - **Management differs:** EM major responds to topical corticosteroids and HSV prophylaxis; SJS requires drug withdrawal and ICU-level care This biopsy showing **full-thickness epidermal necrosis** rules out EM major. ### Special Consideration: HIV + TMP-SMX **High-Yield:** TMP-SMX is the **most common cause of SJS/TEN in HIV patients**, especially with CD4 <200 cells/μL. The risk is 100–1,000 times higher than in immunocompetent individuals. Once SJS/TEN develops from TMP-SMX, the patient must **never receive sulfonamides again**. Alternative PCP prophylaxis options: - **Dapsone** (if no sulfonamide allergy) - **Atovaquone-proguanil** - **Pentamidine** (inhaled or IV) - **Clindamycin-primaquine** 
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