New observations on the fine structure of lamellar ichthyosis and the effect of treatment with etretinate.

Light and electron microscopy were used to study specimens from four patients suffering from lamellar ichthyosis. Three of these patients had been treated with etretinate for 10 months. Biopsy specimens taken from the patients before treatment showed hyperkeratosis with focal parakeratosis, a thickened granular layer in which the cellular content of tonofibrils and keratohyalin was moderately diminished, and acanthosis with increased cellular activity. During treatment with etretinate there was moderate clinical improvement. The most conspicuous microscopic change was thinning of the cornified layer. The intercellular spaces of the epidermis showed increased amounts of fine and coarse granular substance. The number of keratinosomes was increased. Stimulation of Langerhans' cells was observed. Two new ultrastructural findings in lamellar ichthyosis were discovered. First, the marginal band of the cornified layer was absent in conventional glutaraldehyde-osmium tetroxide fixation. Second, the corneocytes contained electron-lucent crystals. The treatment with etretinate did not influence these structures. The mechanism of action of retinoids in lamellar ichthyosis is discussed.