Sweat testing in hypomelanosis of Ito: divergent results reflecting genetic heterogeneity.

Sweat testing using a modified version of the method described by Minor was performed in 5 children affected with hypomelanosis of Ito. In 4 cases the areas of hypopigmentation were arranged in patterns following the lines of Blaschko, whereas in one case a phylloid pattern was observed. In 4 cases the hypomelanotic areas were shown to be anhidrotic. In one case of hypomelanosis following Blaschko's lines, sweat testing was normal and did not reveal any functional difference between the normally pigmented and the hypopigmented areas. These results provide a clinical illustration of the fact that hypomelanosis of Ito is not an entity but constitutes a cutaneous manifestation of various states of mosaicism.