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.