Congenital Nevi: Accuracy of Relative Area Index Measurements

To the Editor.— In the November 1986 issue of theArchives, Rhodes1emphasizes that the growth rate of a congenital nevocytic nevus (CNN) must be compared with the growth rate of the skin in general. I agree fully with Rhodes, and I have previously2criticized the division of CNN into small, medium, and large, based on nevus size alone and without regard to body surface area (BSA). In an attempt to improve classification of CNN, I have suggested the use of a relative area index (RAI)2RAI = 100 × Nevus Area/BSA where nevus area and BSA are expressed in square meters. The value of BSA is obtained using DuBois' formula.2,3However, when BSA is less than 0.6 m2, Boyd's formula2,4is preferred. However, RAI has an obvious disadvantage, and that is (as pointed out by Rhodes1) that different parts of the body grow at different rates. The surface area of the head expands less and the thighs and legs