1. What is BSA in Psoriasis?

Body Surface Area (BSA) affected by psoriasis is a key measure of disease severity. It estimates the percentage of skin covered by psoriatic lesions, with one palm area representing approximately 1% of total BSA.

2. How Does the Calculator Work?

The calculator uses either the palm method or visual estimation:

Where:

• 1 palm = patient's palm including fingers ≈ 1% of total BSA
• Visual estimation divides body into regions with known BSA percentages

Explanation: The palm method is simple and practical for clinical use, while visual estimation may be more accurate for experienced clinicians.

3. Importance of BSA Measurement

Details: BSA assessment helps determine psoriasis severity (mild: <3%, moderate: 3-10%, severe: >10%), guide treatment decisions, and monitor treatment response over time.

4. Using the Calculator

Tips: Count how many palm-sized areas are affected or visually estimate the percentage coverage. Enter the total number of palms affected (can use decimals for partial palms).

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the palm method?
A: It provides a reasonable estimate (±1-2%) for most adults, as palm size generally correlates with body size.

Q2: What about children?
A: Children's palms represent a larger percentage of their BSA (about 1.5-2% in infants). Age-specific charts should be used.

Q3: How is BSA used in treatment decisions?
A: Many guidelines use BSA thresholds (e.g., >5% or >10%) to determine eligibility for systemic therapies or biologics.

Q4: Should erythema be included in the measurement?
A: Only clearly demarcated, thickened plaques should be counted, not just erythematous areas.

Q5: Are there digital tools to help measure BSA?
A: Yes, some apps use photographs with body maps to estimate BSA, but the palm method remains the clinical standard.