📊 VASI Vitiligo Area Severity Index Calculator Simulator

Hand-Unit Area Measurement — Mapping Depigmented Patches

The patient's own palm defines a one-percent body surface unit.

• ~1%: Hand unit value (of total body surface area)
• Palm span: Measurement tool (patient-specific reference)
• 100: Max area score (hand units across body)
• Clinical exam: Use case (bedside area estimation)

Counting hand units across depigmented patches

Each patch is compared visually against the palm-sized unit.

Placeholder: hand-unit counting standardizes area estimates across examiners.

Body Region Percentage Involvement — Weighted Anatomic Zones

Standard body regions carry fixed maximum surface area weights.

• 5: Regions tracked (face, trunk, arms, legs, extremities)
• ~36%: Trunk weight (largest single region share)
• ~10%: Face/neck weight (smaller region contribution)
• L/R: Symmetry check (compared per region)

Distributing hand units into anatomic regions

Placeholder: each region receives its own hand-unit subtotal.

Placeholder: regional weighting prevents overestimating small body areas.

Degree of Depigmentation Grading — Zero to One Hundred Percent

Each patch receives a pigment-loss grade in ten percent steps.

• 0-100%: Grading scale (pigment loss per patch)
• 10%: Common steps (incremental grading resolution)
• 100%: Full loss grade (completely depigmented patch)
• 0%: Repigmented grade (normal skin tone restored)

Visual grading of residual pigment within patches

Placeholder: examiners estimate remaining pigment fraction by eye.

Placeholder: consistent grading improves treatment response tracking over time.

Region-Weighted Area Calculation — Combining Area and Degree

Regional area is multiplied by its depigmentation degree fraction.

• A × D: Formula (area times degree per region)
• HU score: Output units (weighted hand-unit subtotal)
• Region %: Per-region max (if fully depigmented)
• Sum all: Aggregation (regions combined next stage)

Multiplying area by depigmentation degree per region

Placeholder: this weighting reflects both extent and intensity of loss.

Placeholder: a small fully-depigmented patch can outweigh a large faint one.

Total VASI Score — Final Zero to One Hundred Index

All region-weighted subtotals sum into one severity index.

• 0-100: Score range (total VASI index value)
• <10: Mild threshold (limited disease extent)
• >50: Severe threshold (extensive depigmentation)
• Trials: Clinical use (treatment response endpoint)

Interpreting the final composite VASI score

Placeholder: higher scores indicate more extensive, deeper pigment loss.

Placeholder: VASI tracks treatment response across repeated clinic visits.