Alopecia: histologic diagnosis by transverse sections

Histologic evaluation for alopecia can be difficult and in part can be attributed to confusing categorization and limited information derived from examination of traditionally prepared biopsy specimens. The transverse section technique has many advantages, and with experience is the preferable method for evaluating specimens for alopecia. Using this technique, numerous follicles can easily be seen in one tissue profile allowing evaluation of follicular density, follicular unit morphology, and follicular growth dynamics, ie, anagen-telogen ratio. Specimens are categorized as scarring or nonscarring alopecia, and further diagnostic criteria discussed herein assist the pathologist in making specific diagnoses of nonscarring and scarring alopecias. Scarring alopecia may be primary or secondary, and primary scarring alopecias are further classified as lymphocyte-associated and neutrophil-associated. Although the clinical impression is very important in diagnosing alopecia, transversely sectioned biopsy specimens can greatly aid the diagnosis and management of patients with alopecia.