Epilepsy & Seizures
Epileptic lesions due to malformation of cortical development
Sep. 06, 2023
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The term “hypomelanosis of Ito” encompasses a heterogeneous group of disorders characterized by hypopigmented skin lesions arranged in whorls, streaks, or both, along the lines of Blaschko (a nonrandom developmental system of cutaneous markings characterizing the distribution of various linear and segmental skin disorders). Even though Ito's original report in 1952 described a purely cutaneous disease, subsequent case reports and case series have recorded a significant association with multiple extracutaneous manifestations, including musculoskeletal and neurologic abnormalities. For hypomelanosis of Ito several models of inheritance have been proposed but not proved, and a number of cytogenetic studies have revealed a wide variety of mosaic chromosomal abnormalities, hence, the heterogeneity of associated systemic features. Thus, it has been suggested that this group of conditions is rather a nonspecific manifestation (ie, a phenotype) reflecting genetic mosaicism. These mosaic phenomena likely disrupt expression or function of pigmentary genes.
• Hypomelanosis of Ito is a sporadic neurocutaneous disorder characterized cutaneously by hypopigmented skin lesions arranged in whorls and streaks along the lines of Blaschko.
• Though multisystem involvement is common, it is heterogeneous in presentation and commonly manifests with involvement of the neurologic and musculoskeletal systems.
• The most common neurologic manifestations include cognitive and behavioral problems in up to 70% and epilepsy in up to 50%.
• Neuroimaging findings can include cerebral or cerebellar atrophy, cerebral dysgenesis, or migrational abnormalities.
Lines of Blaschko. Alfred Blaschko (1858 to 1922) was a private practitioner of dermatology in Berlin whose interests ranged from leprosy to occupational skin diseases (07).
In 1901 he presented his original description on the distribution patterns of linear skin disorders after having examined more than 140 patients with linear lesions such as epidermal nevi, sebaceous nevi, and nevus lipomatosus, and after carefully transposing the pattern in each patient onto dolls and statues (06; 30; 07).
A composite diagram of these distribution patterns was then drawn that has subsequently been referred to as the lines of Blaschko. In 1976, Jackson introduced the concept of the lines of Blaschko into the English-language literature, although it had been well known in the European community for decades (07). Happle added to Blaschko’s original diagram lines (confined to the trunk and limbs) localized to the posterior scalp (24; 07; 26).
Hypomelanosis of Ito. In 1952 Minor Ito described a 22-year-old Japanese girl whose skin of the upper half of her body looked as “if the normal pigment was brushed off.” The depigmented skin lesions were widespread and symmetric, arranged in irregular shapes with “zigzag borders and splash-like spots” on the trunk and in a “linear pattern” down her arms. He defined these lesions as “nevus depigmentosus systematicus bilateralis” (29). No other physical abnormality was reported apart from asymmetry of breast size. At that time, Ito coined the term incontinentia pigmenti achromians (44) because the pattern of color loss was similar to that of the hyperpigmented changes seen in incontinentia pigmenti of the Bloch-Sulzberger type (OMIM #308300). Subsequent observations expanded the phenotype and the name hypomelanosis of Ito was proposed to avoid confusion with incontinentia pigmenti (31). However, this term was criticized because Ito’s original patient was described as having “depigmented,” not hypopigmented lesions (29; 60; 61; 50). Possibly, the original patient by Ito may have had incontinentia pigmenti, as the author himself believed (29). Further terms have been used such as Ito disease, Ito syndrome, and Ito hypomelanosis.
Proposed changes in terminology included the terms pigmentary dysplasia, mosaic dyspigmentation, pigmentary mosaicism, pigmentary mosaicism of the Ito type, or hypopigmentation along the lines of Blaschko to reflect the disease pathogenesis or recall the cutaneous patterns (11; 60; 14; 36; 61; 50; 44). Despite these criticisms the term hypomelanosis of Ito is still used.
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