Distinctive histopathologic findings in linear morphea (en coup de sabre) alopecia

Linear morphea en coup de sabre is a localized form of morphea that presents as paramedian face or frontal scalp depression. The histopathology of alopecia in linear morphea is typically characterized by sclerosis and a reduction in the number of follicular units. We present a 26-year-old Caucasian female with a 1.5-year history of linear morphea and alopecia with unique atrophic follicular remnants on scalp biopsy. Transverse and vertical sections of biopsy specimens showed dense, dermal sclerosis with marked eccrine gland atrophy and replacement of much of the adipose by collagenous tissue. All sebaceous glands had disappeared, but erector pili muscles persisted. Numerous vertical, columnar and epithelial structures were present at the sites of formerly viable hair follicles. Transverse sections of these atrophic follicular remnants had a resemblance to telogen follicles but were microscopically different. The morphology of these follicular remnants indicates an end-stage process or permanent alopecia. Similar follicular remnants have been reported in chemotherapy-induced permanent alopecia but not in alopecia secondary to morphea or other cicatricial alopecias. We discuss the significance of these findings and their relationship to other forms of cicatricial or permanent alopecia based on the literature and case review.