Novel Potential Histologic Clues to Mechanical Alopecia: A Comparative Study of Traction Alopecia, Trichotillomania, and Approximately Age/Gender Matched Controls.

Mechanical stress on the pilosebaceous unit can contribute to mechanical alopecia (MA) as seen with traction alopecia (TA) and trichotillomania (TTM). While some histological features that point to TA and TTM have been described, these may be absent in biopsies obtained at earlier stages of disease. Additional anomalies of the pilosebaceous unit have been observed that may assist in the histopathological detection of MA. A blinded, retrospective, qualitative, and semiquantitative study was performed comparing horizontally processed scalp biopsy sections of clinicopathologically confirmed TA (n = 16) and TTM (n = 9) to nearly matched controls (n = 15). Translocation of sebocytes into the follicular canal was seen in both TA and TTM, supporting a shared underlying mechanism. Vectorially warped sebaceous lobules were observed predominately in TA (p = 0.0002), while collapse of the inner root sheath of the lower follicular isthmus and surface lichenification were primarily seen in TTM (p < 0.0002). Lateral impingement of the follicular canal was seen in both TA and TTM (p < 0.0001), although more commonly in TA. These alterations were observed in the absence of other previously described features. Further validation studies in larger cohorts are warranted to assess their diagnostic utility in the recognition of MA.