Hypomelanosis of Ito: clinical syndrome or just phenotype?

The term hypomelanosis of Ito is applied to individuals with skin hypopigmentation along the lines of Blaschko. Even though originally described as a purely cutaneous disease, subsequent reports have included a 33% to 94% association with multiple extracutaneous manifestations mostly of the central nervous and musculoskeletal systems leading to frequent characterization as a neurocutaneous disorder. A number of reports claimed familial occurrence and supported single gene inheritance for hypomelanosis of Ito, but none has been proved. Miscellaneous chromosomal mosaicisms have been demonstrated in some but not all affected individuals. Thus, it has been suggested that hypomelanosis of Ito is not a single condition but rather a nonspecific manifestation (ie, a phenotype) of chromosomal mosaicism and that this term should now be dropped. In this article, we review these developments focusing on the neurologic and genetic aspects of hypomelanosis of Ito. Our personal experience with 41 hypomelanosis of Ito patients and literature review led us to conclude that (1) the term hypomelanosis of Ito has been often misapplied to individuals with nonspecific "patchy depigmentation of the skin" who had several conditions of different etiologies; (2) the white matter involvement seen at neuroimaging in most of our hypomelanosis of Ito patients was similar to that reported in well-defined neurocutaneous disorders, including Sjögren-Larsson syndrome and incontinentia pigmenti; (3) whatever figures we take for associated central nervous system abnormalities in hypomelanosis of Ito, these represent the most frequent extracutaneous findings and, therefore, the use of the term neurocutaneous disorder for hypomelanosis of Ito might well be appropriate.