What diagnostic tests are recommended for a patient suspected of having Stevens-Johnson (SJS) syndrome?

Diagnostic Tests for Stevens-Johnson Syndrome (SJS)

For patients with suspected Stevens-Johnson syndrome, a skin biopsy is the critical diagnostic test that should be performed immediately to confirm the diagnosis, as it reveals characteristic histopathological features including epidermal damage and subepidermal vesicle/bulla formation. 1

Initial Clinical Assessment

• Complete examination of skin and all mucous membranes (oral, ocular, genital) to assess:

  • Extent of skin involvement (% body surface area affected)
  • Presence of target lesions, purpuric macules, blisters
  • Positive Nikolsky's sign (epidermis separates from dermis with gentle lateral pressure)
  • Mucosal involvement (eyes, mouth, genitalia)

• Document all medications taken in the previous 2 months, including over-the-counter preparations and complementary therapies 1

Essential Diagnostic Tests

1. Skin Biopsy:

   • Most important diagnostic test
   • Histopathological features: epidermal damage, subepidermal vesicle/bulla formation
   • Shows satellite cell necrosis in early stages progressing to full thickness necrosis of the epidermis 1

2. Ophthalmological Examination:

   • Must be performed within 24 hours by an ophthalmologist
   • Assesses for conjunctival hyperemia, pseudomembrane formation, and epithelial defects 1

3. Laboratory Tests:

   • Complete blood count with differential
   • Comprehensive metabolic panel (liver and kidney function)
   • Blood cultures if infection is suspected 1
   • Consider investigating potential infectious triggers (e.g., mycoplasma) especially in mild cases with predominant mucositis 1

SCORTEN Score Calculation

Calculate the SCORTEN score within the first 24 hours to predict mortality risk:

• Age >40 years (1 point)
• Heart rate >120 bpm (1 point)
• Cancer/hematological malignancy (1 point)
• Epidermal detachment >10% body surface area (1 point)
• Serum urea >10 mmol/L (1 point)
• Serum glucose >14 mmol/L (1 point)
• Serum bicarbonate <20 mmol/L (1 point) 1

Additional Considerations

• Drug Hypersensitivity Testing: Routine drug hypersensitivity testing is not recommended following an episode of SJS/TEN 2

• In Vitro Tests: In specific cases where the culprit drug cannot be identified with confidence, specialized testing may be considered:

  • Lymphocyte drug-induced IFN-γ assay can be part of the investigative work-up
  • Drug-induced lymphocyte cytokine production tests may be useful 2

• Provocation Tests: Oral provocation studies are contraindicated due to risk of life-threatening reactions 3

Important Clinical Pitfalls

1. Delayed Diagnosis: SJS can progress rapidly, and delayed diagnosis increases mortality risk. Early skin biopsy is crucial even if clinical presentation is not fully developed.

2. Incomplete Medication History: Failing to document all medications taken in the previous 2 months may miss the culprit drug.

3. Overlooking Mucosal Involvement: Comprehensive examination of all mucous membranes is essential as mucosal involvement may precede skin manifestations.

4. Failure to Monitor Progression: Serial assessment and photography are important to document disease progression and response to treatment 2.

5. Misdiagnosis: SJS/TEN can be confused with other conditions like erythema multiforme, staphylococcal scalded skin syndrome, or autoimmune bullous diseases.

By following this diagnostic approach, clinicians can rapidly confirm SJS diagnosis and initiate appropriate management to reduce morbidity and mortality in this life-threatening condition.