Linear and whorled nevoid hypermelanosis versus incontinentia pigmenti: is pigmentary incontinence really a distinctive feature?

This report describes a 3-year-old boy who presented with skin lesions characterized by multiple streaks of hyperpigmentation following Blaschko's lines since 6 weeks of age. The clinical features are consistent with the diagnosis of linear and whorled nevoid hypermelanosis (LWNH), but differ substantially from this entity by the pigmentary incontinence observed on both the paraffin and electron microscopy sections. Despite the presence of pigmentary incontinence, the diagnosis of incontinentia pigmenti (IP) can be ruled out on the basis that the patient is a male, with none of the characteristic anomalies present in this syndrome, and that he never presented with inflammatory or eruptive skin lesions. This observation suggests that pigmentary incontinence may not differentiate IP from LWNH as conclusively as previously reported in the literature.