Ultrastructural study of acquired pili torti-like hair defects accompanying pseudopelade.

Acquired structural hair defects are caused by various physical and chemical manipulations. Plucked hairs and hair follicle biopsy specimens of pili torti-like hairs that arose from pseudopelade scalp were studied. In scanning electron microscopy, the hair shafts had a segmental pili torti-like appearance, accompanied by oblique or longitudinal grooves and ridges. In light microscopy, the hair follicles showed an asymmetric hair bulb and inner root sheath, and a shortened keratogenous zone within sclerosing fibrous connective tissue. In transmission electron microscopy, the numbers and thickness of the hair cuticle cells were different on the opposite sides of the hair shaft. The hair cuticle was irregularly shaped and formed asymmetric waves. The tonofilaments in the hair cortex ran almost parallel to the hair axis. From these findings, it was clear that the grooves and ridges were produced by the deformed hair cuticle and cortex, whose shapes were modulated by the asymmetric inner root sheath. This asymmetry most likely resulted from a dysfunctional dermal papilla, which was affected by fibrosis. The pili torti-like appearance appeared to be caused by the grooves and ridges that ran obliquely on the hair shaft surface.