The infant with Netherton syndrome (NS) typically displays a generalized erythroderma covered by fine, translucent scales, which can be difficult to distinguish clinically from erythrodermic psoriasis, nonbullous congenital ichthyosiform erythroderma, or other infantile erythrodermas. Some infants with NS develop progressive hypernatremic dehydration, failure to thrive, and enteropathy. Such complications can be fatal. Diagnosis is typically delayed until the appearance of a pathognomonic hair shaft anomaly, trichorrhexis invaginata (bamboo hair). To facilitate the early diagnosis of NS, we obtained biopsy specimens from 7 patients with erythrodermic NS and compared their morphologic findings to those of 3 patients with erythrodermic psoriasis and 2 with congenital ichthyosiform erythroderma. Biopsy specimens were processed for light and electron microscopy using postfixation with osmium tetroxide and ruthenium tetroxide.
In NS, and often in congenital ichthyosiform erythroderma and erythrodermic psoriasis, the stratum corneum layer was largely replaced by parakeratotic cells. A distinctive feature—premature secretion of lamellar body contents—occurred only in NS. Furthermore, lamellar body–derived extracellular lamellae and stratum corneum lipid membranes were separated extensively by foci of electron-dense material. Finally, transformation of lamellar body–derived lamellae into mature lamellar membrane structures was disturbed in NS.
Premature lamellar body secretion and foci of electron-dense material in the intercellular spaces of stratum corneum, features not observed in other erythrodermic disorders, appear to be frequent and relatively specific markers for NS. These ultrastructural features could permit the early diagnosis of NS before the appearance of the hair shaft abnormality. These abnormalities could explain the impaired permeability barrier in NS, and account for hypernatremia and dehydration in infants with NS.