The role of the scalp biopsy in the evaluation of alopecia.

A biopsy should be performed whenever the diagnosis is in doubt. A 4-mm punch biopsy sectioned horizontally at multiple levels is best. In general, noncicatricial alopecia should be sampled where hair is sparsest (most involved area), and cicatricial alopecia should be biopsied in an area of active disease, which is best determined using a dermatoscope and is most often at the margin of a lesion. The goal with cicatricial alopecia is to capture both follicular scars as well as actively inflamed hairs. Information provided by the clinician to the pathologist can be decisive in rendering a definitive diagnosis. The wording of the biopsy report provides a clue to the confidence of the pathologist's diagnosis.