1. What is Body Surface Area (BSA) in Psoriasis?

Body Surface Area (BSA) is a measurement used to quantify the extent of psoriasis skin involvement. It's expressed as a percentage of total body surface area affected. 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 two methods:

Where:

• Palm count - Number of palm-sized affected areas
• Large areas - Arms (9% each), Legs (18% each), Chest/Back (18% each), Head (9%)

3. Importance of BSA Calculation

Clinical Significance: BSA assessment helps determine psoriasis severity:

• Mild: <3% BSA
• Moderate: 3-10% BSA
• Severe: >10% BSA

This classification guides treatment decisions and monitors disease progression.

4. Using the Calculator

Instructions:

1. Count palm-sized affected areas (1 palm ≈ 1% BSA)
2. For larger affected areas, select the area type and count
3. The calculator sums all affected areas

5. Frequently Asked Questions (FAQ)

Q1: How accurate is the palm method?
A: The palm method provides a quick estimate. For precise measurement, more detailed methods like the Rule of Nines or digital imaging may be used.

Q2: What if lesions are smaller than a palm?
A: Estimate fractions of a palm (e.g., half palm = 0.5% BSA). Multiple small lesions can be mentally grouped to estimate palm equivalents.

Q3: Does BSA alone determine treatment?
A: No. Treatment decisions also consider lesion location, symptoms, quality of life impact, and treatment history.

Q4: How often should BSA be assessed?
A: At each clinical visit to monitor treatment response, typically every 3-6 months for stable psoriasis.

Q5: Are there digital tools for more precise measurement?
A: Yes, some clinics use digital photography with specialized software for precise BSA calculation, but these are not routinely available.