Pathogenesis in trichorrhexis invaginata (bamboo hair).

The mechanism of formation of trichorrhexis invaginata, which is one of the characteristic hair anomalies seen in Netherton's syndrome, was studied using plucked hairs obtained from 3 patients with the typical clinical features. The biopsy specimens used to examine the hair root were obtained from the scalp of one of the patients and the eyebrow area of the other. The scanning electron microscopic observation of plucked hairs showed trichorrhexis invaginata, tortion nodule, pili torti, and trichorrhexis nodosa. The light microscopic sections of nodules of plucked hairs revealed invaginated hair cuticle into the cortex. Transmission electron microscopy revealed cleavages and electron-dense depositions in the cortex of plucked hair nodules; such changes were not seen in newly formed nodules in follicles in biopsy specimens. In the keratogenous zone, a zigzag pattern of cortical fibers and invaginations of hair cuticle cells into the cortex were observed. Histochemical staining for -SH groups and S-S linkages using N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide (DACM) was performed on frozen sections of plucked hairs from patients and normal controls. Keratinized cortical cells of patients possessed more -SH groups than the controls and a strong fluorescence for -SH was sometimes seen in the cortex of nodules. It is concluded that the invagination of affected hairs is caused by softness of the cortex in the keratogenous zone, which may result from an incomplete conversion from -SH to S-S in proteins in cortical fibers.