What are the diagnostic criteria for Stevens-Johnson syndrome (SJS)?

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Last updated: October 24, 2026 • View editorial policy

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Diagnostic Criteria for Stevens-Johnson Syndrome (SJS)

SJS is diagnosed when epidermal detachment is less than 10% body surface area (BSA) plus widespread purple/red macules or flat atypical targets, distinguished from erythema multiforme major by the presence of flat atypical targets rather than typical raised targets. 1

Clinical Diagnostic Criteria

Essential Features for Diagnosis

Cutaneous Findings:

  • Epidermal detachment <10% BSA (including both detached and detachable epidermis)
  • Widespread purpuric macules or flat atypical targets (not typical raised targets)
  • Positive Nikolsky sign (lateral pressure causes epidermis to slide over dermis)
  • Initial distribution: upper torso, proximal limbs, and face
  • Prominent involvement of palms and soles 2

Mucosal Involvement:

  • Erosive and hemorrhagic mucositis affecting at least two mucosal sites
  • Eyes: purulent keratoconjunctivitis, pseudomembrane formation
  • Mouth: erosions, ulcerations
  • Genitalia: erosions, dysuria
  • Nose: crusting, erosions 2

Prodromal Symptoms (preceding rash by several days):

  • Fever and malaise
  • Upper respiratory tract symptoms
  • Cutaneous pain (prominent early feature that should alert clinicians)
  • Ocular inflammation may precede skin signs 2

Spectrum Classification

The British Association of Dermatologists guidelines 1 define the SJS/TEN spectrum as:

  • SJS: <10% BSA detachment + widespread purpuric macules/flat atypical targets
  • Overlap SJS-TEN: 10-30% BSA detachment + widespread purpuric macules/flat atypical targets
  • TEN: >30% BSA detachment

Critical Distinction from Erythema Multiforme Major (EMM)

Key differentiating features:

  • SJS: Flat atypical targets, widespread distribution, primarily drug-induced
  • EMM: Typical targets or raised atypical targets, localized to limbs/extremities, primarily HSV-related
  • EMM does not progress to SJS/TEN and patients remain constitutionally well 1, 2

This distinction has critical causality implications - misclassification may lead to incorrect attribution of drug causation when HSV is the actual trigger.

Confirmatory Investigations

Histopathology (Essential but Should Not Delay Treatment)

Two biopsies required: 2

  1. Lesional skin biopsy (adjacent to blister) for routine histopathology
  2. Periblister lesional skin sent unfixed for direct immunofluorescence to exclude immunobullous disorders

Expected histological findings: 1

  • Variable epidermal damage: individual cell apoptosis to confluent epidermal necrosis
  • Basal cell vacuolar degeneration
  • Subepidermal vesicle or bulla formation
  • Mild perivascular lymphocytic infiltrate in dermis
  • Small numbers of eosinophils may be present

Initial Laboratory Assessment 2

Mandatory investigations:

  • Full blood count, ESR, CRP
  • Urea and electrolytes, magnesium, phosphate, bicarbonate, glucose
  • Liver function tests, coagulation studies
  • Mycoplasma serology (especially in children with predominantly mucosal involvement)
  • Chest X-ray
  • Swabs from lesional skin for bacteriology
  • Photographs documenting lesion type and extent

Documentation Requirements

Body surface area assessment: 2

  • Record extent of erythema separately from extent of epidermal detachment on body map
  • Use Lund and Browder chart for BSA calculation
  • Detachment includes both detached AND detachable epidermis (Nikolsky-positive areas)
  • The detachment figure (not erythema) has prognostic value

Common Diagnostic Pitfalls

  1. Confusing SJS with EMM - Look specifically for flat vs. raised targets and distribution pattern
  2. Underestimating BSA - Must include detachable (Nikolsky-positive) epidermis, not just visibly detached areas
  3. Delaying treatment for biopsy confirmation - Biopsy supports diagnosis but treatment should begin immediately when clinical suspicion is high 1, 3
  4. Missing Mycoplasma-associated cases - Particularly in children with predominant mucositis and minimal cutaneous involvement 2
  5. Attributing to paracetamol/ibuprofen - These are likely confounders used to treat prodromal symptoms, though rare causative cases exist 1

Drug Causality Assessment

Timeline analysis is critical: 2

  • Most likely latency: 5-28 days after drug initiation
  • Shorter latency possible with previous exposure to same drug
  • Consider drug half-life and pharmacokinetics
  • ALDEN algorithm can help define drug causality post-acute phase
  • High-risk drugs: anticonvulsants, antibiotics, allopurinol, NSAIDs (excluding paracetamol/ibuprofen confounders) 1

References

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