A clinico-pathological and EM study of a Thai boy with hypomelanosis of Ito, one of the neurocutaneous syndromes, is reported. At birth, typical skin hypopigmentation on the trunk and a hypopigmented streak on the left lower extremity were noted. Associated cutaneous pathology shows a decrease of melanin granules within basal and malpighian keratinocytes. Ultrastructural studies highlight a normal appearance for basal and malpighian keratinocytes, but a lack of melanosomes in the malpighian cells. Melanosomes are also dramatically reduced in the basal keratinocytes, which appear small, single or clustered and surrounded by a membrane. Melanocytic degeneration has been observed and dendritic melanocytes contained various stages of nonmelanised (stage II), partially melanised premelanosome (stage III) and rarely stage 4 melanosomes. The authors observed an increase in the number of Langerhans cell which have not previously been described. There were unmyelinated axon of nerve containing melanosomes at the dermoepidermal junction. The significance of these findings will be worthwhile to note that abnormal nerve termination in close relationship with basal keratinocyte, degenerated melanocyte, premelanosomes and langerhans cell are important in explaining the pathogenesis of Hypomelanosis of Ito.

Keywords: Hypomelanosis of Ito (incontinentia pigmenti achromians), Ultrastructural study