BSA Assessment — SCE Dermatology MCQ

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EasyInflammatory DermatosesBSA AssessmentSCE Dermatology

A 60-year-old man with severe psoriasis is being assessed using the BSA (body surface area) method. He is asked to use his palm as a reference. The patient's palm (including fingers) represents what percentage of their total BSA?

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Correct answer: B — Approximately 1% of total BSA

The patient's palm (including fingers) represents approximately 1% of their total body surface area. This is the basis of the 'palmar method' used for quick BSA estimation in psoriasis, eczema, and burns assessment. For psoriasis: PASI incorporates BSA assessment within each body region. For burns (Wallace rule of nines): head 9%, each arm 9%, each leg 18%, anterior trunk 18%, posterior trunk 18%, perineum 1%. The palmar method is most useful for estimating small or patchy areas of involvement. It tends to slightly overestimate BSA in adults (true palm-only area is approximately 0.5%, palm + fingers approximately 0.8-1%). Despite this minor inaccuracy, it remains a practical bedside tool.

Reference: BAD 2020 Psoriasis; Burns Guidelines