Alopecia Areata Workup

Updated: Jun 27, 2023
  • Author: Chantal Bolduc, MD, FRCPC; Chief Editor: Dirk M Elston, MD  more...
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Diagnosis usually can be made on clinical grounds; a scalp biopsy seldom is needed, but it can be helpful when the clinical diagnosis is less certain.


Histologic Findings

A histologic diagnosis of alopecia areata can be made when characteristic features are present. Horizontal sections usually are preferred to vertical sections because they allow examination of multiple hair follicles at different levels.

The most characteristic feature is a peribulbar lymphocytic infiltrate, which is described as appearing similar to a swarm of bees. The infiltrate often is sparse and usually involves only a few of the affected hairs in a biopsy specimen. Occasionally, no inflammation is found, which can result in diagnostic difficulties. A significant decrease in terminal hairs is associated with an increase in vellus hairs, with a ratio of 1.1:1 (normal is 7:1). Other helpful findings include pigment incontinence or the presence of eosinophils in the follicular stellae, multiple catagen hairs, hyperkeratosis of the infundibulum, and pigment casts in the infundibulum.

A shift occurs in the anagen-to-telogen ratio, which is not specific. The normal ratio is approximately 90% anagen phase to 10% telogen phase hair follicles; in alopecia areata, 73% of hairs are found to be in the anagen phase and 27% in the telogen phase. In long-standing cases of alopecia areata, the percentage of telogen-phase hairs can approach 100%. Degenerative changes of the hair matrix can be found but are uncommon.