Hypomelanosis of Ito
A similarly named but quite distinct neurocutaneous syndrome was reported by Ito (1952) as 'incontinentia pigmenti achromians' with cutaneous whorls and streaks, zig-zag or marbled areas of hypopigmentation which may increase with age and contrast with the normal, darker skin. The lesions may be unilateral or bilateral, occurringanywhere on the body, except for the palms, soles, scalp mucosae. They often follow the lines of Blaschko. They are best seen with ultraviolet light (Fig. 21.18). Neurological symptoms occur in half the cases. The disorder differs from incontinentia pigmenti in that it affects males and females alike and does not show melanin in the dermis. For these reasons, it seems appropriate to use another name, and the term 'hypomelanosis of Ito' was suggested (Jelinek et al 1973).
Reviews are given by Glover et al (1989), Golden & Kaplan (1986) and Gordon (1994). Of 19 cases diagnosed at the Hospital for Sick Children, London, over 5 years (Glover et al 1989), 14 were developmentally delayed, nine had a history of seizures, two had sensorineural deafness and three had severe ocular abnormalities. Hemihypertrophy was present in four cases, syndactyly in three, and scoliosis in one. Nine out of 17 examined had abnormal CT brain scans, four showing evidence of abnormal neuronal migration. Four children had cutaneous abnormalities only. There were no familial cases in this series.
Biopsy of hypopigmented skin in one patient showed decreased or absent melanin granules in the basal epidermal layers (Hamada et al 1979).
Neuropathological reports are few; that of Ross et al (1982) described macrocephaly and heterotopias of grey matter, while Malherbe et al (1993) reported macrocephaly and neuronal migration defects. Neuronal migration defects are suggested by CT or MRI scan findings in some patients with this syndrome, as in other neurocutaneous syndromes. A disorder of neural crest cell migration in the second trimester may be responsible for the neurological and skin features.
Genetics
Most reported cases appear to be sporadic. Chromosome anomalies have been found in a few patients (Miller & Parker 1985, Golden & Kaplan 1986).Although normal karyotypes have often been found in peripheral blood lymphocytes, chromosomal mosaicism has been shown in skin fibroblasts and/or lymphocytes in many cases (Rott et al 1986, Glover et al 1989). The recurrence risk is low unless a parent also shows mosaicism (Harper 1994).
