1. What is BSA in Psoriasis?

Body Surface Area (BSA) assessment is a crucial measure in psoriasis to determine disease severity and guide treatment decisions. The palm method (1 palm ≈ 1% BSA) is commonly used in clinical practice for quick estimation.

2. How Does the Calculator Work?

The calculator uses the palm method equation:

Where:

• Head ≈ 9% of total BSA
• Each arm ≈ 9% of total BSA
• Trunk (front and back) ≈ 36% of total BSA
• Each leg ≈ 18% of total BSA

Explanation: The calculator sums the affected percentages from each body region to estimate total BSA involvement.

3. Importance of BSA Calculation

Details: BSA assessment helps classify psoriasis severity (mild <3%, moderate 3-10%, severe >10%) and guides treatment selection, including eligibility for systemic therapies or biologics.

4. Using the Calculator

Tips: Estimate the percentage of each body region affected by psoriasis. One palm (including fingers) represents approximately 1% of total BSA. Enter values for each region to calculate total involvement.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the palm method?
A: The palm method provides a quick estimate. For precise measurement, tools like the Psoriasis Area Severity Index (PASI) may be used.

Q2: What counts as affected area?
A: Only areas with active psoriasis lesions should be counted, not just erythema or residual discoloration.

Q3: How does BSA relate to treatment decisions?
A: Treatment guidelines often recommend systemic therapy for >10% BSA involvement or >3% with significant impact on quality of life.

Q4: Should nails be included in BSA calculation?
A: Nail psoriasis is typically assessed separately, though severe nail involvement may influence treatment decisions regardless of BSA.

Q5: How often should BSA be reassessed?
A: During active treatment, BSA should be reassessed every 3-6 months to evaluate treatment response.