Linear whorled naevoid hypermelanosis (LWNH) is a rare skin condition, characterized by swirls and whorls of hyperpigmented macules distributed in a reticulate pattern along the lines of Blaschko. We report a 2-year-old boy who presented with linear and whorled hyperpigmentation on his trunk and limbs, following the lines of Blaschko. Hyperkinesia and developmental speech-language impairment were also present. A biopsy specimen showed increased pigmentation within the basal keratinocytes without incontinentia pigmenti. No chromosomal abnormality was found in peripheral blood samples. Chromosomal analysis of skin fibroblasts detected trisomy 4 mosaicism. This case shows for the first time an association of LWNH with trisomy 4 mosaicism. LWNH should not be considered a single entity, but a cutaneous expression of mosaicism.
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