Comparison between Langerhans cell concentration in lichen planopilaris and traction alopecia with possible immunologic implications.

Lichen planopilaris and long-standing traction alopecia are both traditionally classified as scarring alopecias. The etiology of lichen planopilaris has not been fully elucidated, although an autoimmune mechanism is generally accepted with Langerhans cell involvement implicated in previous studies. The etiology of traction alopecia is generally considered to be the result of mechanical force with subsequent inflammation without an autoimmune component. Langerhans cells in pure traction alopecia have not been previously evaluated nor have Langerhans cell concentrations been compared among the scarring alopecias. We performed double immunostaining with CD1a and CD3 to assess the ratio of Langerhans cells to T lymphocytes in lichen planopilaris and traction alopecia. Sixteen biopsies were evaluated including 9 biopsies of lichen planopilaris and 7 biopsies of traction alopecia. The mean ratio of the concentration of Langerhans cells to T lymphocytes was 1.28 for the lichen planopilaris group and 0.59 for the traction alopecia group. There is a significantly higher ratio of Langerhans cells to T lymphocytes in lichen planopilaris compared with that seen in traction alopecia. This supports previous data recognizing an immune component in lichen planopilaris mediated by Langerhans cells while emphasizing that most traction alopecias are not primarily immune related. Thus, the traditional classification systems for alopecia may need review and revision, especially when looking at etiopathogenesis. However, rare cases of traction alopecia demonstrated ratios similar to those seen in lichen planopilaris. These cases may represent the recently described "traction alopecia" condition, cicatricial marginal alopecia or changes seen in long-standing lesions, emphasizing the need for inclusion of distribution and duration within the clinical information.