How do I calculate the total body surface area involvement in Stevens‑Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN)?

How to Calculate Total Body Surface Area (TBSA) in SJS/TEN

In SJS/TEN, you must calculate and document TWO separate measurements using the Lund and Browder chart: (1) the percentage of body surface area with erythema, and (2) the percentage with epidermal detachment—it is the detachment figure, not erythema, that determines disease classification, prognosis, and management decisions. 1, 2

What to Measure and Why

The Critical Distinction: Erythema vs. Detachment

• Record the extent of erythema separately from epidermal detachment on a body map 1, 2
• The percentage of epidermal detachment has prognostic value, while erythema alone does not 1, 2
• Epidermal detachment includes:
  • Already detached epidermis (visible erosions and blisters) 2
  • Detachable epidermis (areas with positive Nikolsky sign—where gentle lateral pressure causes the epidermis to slide over the dermis) 2, 3

Disease Classification Based on Detachment Percentage

The British Association of Dermatologists guidelines define three categories based solely on the extent of epidermal detachment 1, 2:

• SJS: <10% BSA epidermal detachment plus widespread purpuric macules or flat atypical targets 2, 3
• SJS-TEN overlap: 10-30% BSA detachment plus widespread purpuric macules or flat atypical targets 2, 3
• TEN: >30% BSA detachment with or without widespread purpuric macules or target lesions 2, 3

Step-by-Step Calculation Method

Use the Lund and Browder Chart

• The Lund and Browder chart is the recommended tool for estimating the percentage of BSA involved 1
• This chart accounts for age-related variations in body proportions, making it more accurate than the "rule of nines" (particularly important in pediatric cases) 1

Documentation Process

1. Perform a complete physical examination of the skin, looking for target lesions, purpuric macules, blisters, and areas of epidermal detachment 1
2. Create a body map marking two distinct parameters 1:
   • Areas of erythema (in one color)
   • Areas of epidermal detachment (in another color)
3. For epidermal detachment, include:
   • Visible denuded areas where epidermis has already separated 2
   • Areas where the Nikolsky sign is positive (detachable but not yet separated epidermis) 2
4. Calculate the percentage for each parameter using the Lund and Browder chart 1

Clinical Application and Pitfalls

Why This Matters for Management

• Patients with >10% BSA epidermal detachment require immediate transfer to a burn center or ICU with SJS/TEN experience 2
• The detachment percentage is used in the SCORTEN scoring system to predict mortality 2
• Wound management approach differs based on extent: conservative for limited detachment, surgical for >30% BSA with clinical deterioration 2

Common Pitfalls to Avoid

• Do not use erythema percentage for classification—only the detachment figure determines whether a patient has SJS, overlap, or TEN 1, 2
• Do not overlook detachable epidermis—areas with positive Nikolsky sign must be included in your detachment calculation even if the epidermis hasn't visibly separated yet 2
• Reassess progression—monitor for increasing detachment, as this indicates worsening disease and may change management 2
• Document both measurements within 24 hours of diagnosis to establish baseline and guide prognostic discussions 1

Practical Example

A patient may have 65% BSA with erythema but only 10% BSA with actual epidermal detachment 1. This patient would be classified as SJS-TEN overlap (based on the 10% detachment), not TEN, despite the extensive erythema. The 10% detachment figure is what determines transfer decisions, SCORTEN calculation, and treatment intensity 1, 2.