Heal House Vitiligo Research 49 · Original Article
How can you accurately measure the area of vitiligo on the face?
Development and validation of the fingertip unit for assessing Facial Vitiligo Area Scoring Index.
In short
Using the concept of a 'fingertip unit' used when squeezing ointment as a ruler, we developed a method to accurately measure the area of facial vitiligo without special equipment.
Vitiligo on the face is the area that concerns patients the most. However, accurately measuring its area has always been a challenge. This is because when assessed as part of the total body surface area, small changes on the face can easily be overlooked. Therefore, I wanted to create a simple ruler that could be used directly in the clinic without special equipment. This study began with the idea of borrowing the concept of the 'fingertip unit' used when applying ointment.
Q1 What does it mean to measure the face area using the tip of one finger?
The fingertip unit originally refers to the amount of ointment squeezed out along the length of one fingertip segment. We used this as a reference ruler for measuring area. Measurements from 98 healthy volunteers (ages 2 to 69) showed that one entire hand corresponds to approximately 32 fingertip segments. This value was remarkably consistent regardless of age, sex, or ethnicity. Therefore, by counting and adding up how many fingertip segments a facial lesion covers, you can express the area of facial vitiligo as a number without any equipment. This number is the facial vitiligo area score, which ranges from 0 to 112. Since your own hand becomes the ruler, the greatest advantage is that anyone can use it intuitively in the clinic.
Q2 Is this measurement reliable in practice?
Yes, it was very accurate and consistent. Six raters measured 11 patients with facial vitiligo twice, at two-week intervals. The results showed that the measured values matched the actual area almost perfectly. The results were consistent whether the same person measured again or a different person measured. In the table below, a number closer to 1 means 'reliable.' Also, a change of only about 2.2 fingertip units can be recognized as a real change, allowing sensitive detection of how much the face has improved with treatment. The fact that this level of reliability was achieved without complex equipment is the true value of this tool.
Validation results of the accuracy and reliability of the facial vitiligo area score measurement
| Item | Value | In simple terms |
|---|---|---|
| Accuracy (Concordance Correlation Coefficient, CCC) | 0.946 | Near-perfect agreement |
| Intra-rater reliability (ICC) | 0.903 | Consistent when the same person measures again |
| Inter-rater reliability | 0.903 | Consistent when a different person measures |
| Minimum detectable change | 2.2 FTU | A change of this amount is recognized as a real change |
Closing remarks
Thanks to this tool, I can now quickly and consistently record changes in facial vitiligo in the clinic using just one hand. In clinical trials, it also allows the face to be evaluated separately and in the same way, making it much easier to compare different studies. After all, in actual clinical practice, a 'simple ruler that anyone can use in the same way' is more powerful than fancy equipment.
