Case: Linear and whorled hypopigmentation

• What's the diagnosis?

• How would you treat her?

Hypopigmentation and hyperpigmentation along the lines of Blaschko is characterized by asymmetrical or symmetrical and localized or widespread dyschromia, usually noted at birth or within the first year of life. The defect in skin color may appear in clusters of small macules or patches forming whorls or streaks, and is most commonly seen on the trunk and extremities. Vesiculation or other signs of inflammation do not precede the pigmentary changes. Although there are reports of familial occurrence, most cases are sporadic.

Lines of Blaschko

In 1901, Dr. Alfred Blaschko noted a distinctive linear and whorled pigmentary pattern of the skin in over 100 patients. In incontinentia pigmenti, this pattern was attributed to X-chromosome inactivation. Dr. Rudolf Happle later expanded this concept to reflect disorders with genetic mosaicism, either due to functional mosaicism resulting from lionization or due to somatic gene mutation or chromosomal non-disjunction.¹

Hypomelanosis of Ito?

The patient's mother had been reading about hypomelanosis of Ito, which represents a select subset of patients with pigmentary mosaicism. Three-quarters of children in this subset were noted to develop systemic manifestations involving the central nervous system, musculoskeletal system, viscera, eyes, hair, or nails.^2,3 Neurological symptoms including seizures, mental retardation, and developmental delay occurred in over 70% of patients during the first decade of life. Autism and microcephaly were also described in these patients.

More recent series suggest that terms like hypomelanosis of Ito are antiquated, and the reported high incidence of anomalies generate unnecessary anxiety among practitioners and parents.^4,5 Over a decade ago, investigators emphasized that the 75% incidence of associated systemic anomalies was a bias of reporting. In 1996, Nehal et al showed that the risk of extracutaneous anomalies was usually less than a third in a series of 54 children with pigmentary features of hypomelanosis of Ito, linear and whorled hypermelanosis, and nevus depigmentosus.⁴ The authors of a more recent series suggested that there is little or no risk in localized lesions, and minimal risk in more widespread lesions.⁵

Differential diagnosis