What is the most characteristic histologic feature in alopecia areata?

Updated: Jun 07, 2018
  • Author: Chantal Bolduc, MD, FRCPC; Chief Editor: Dirk M Elston, MD  more...
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Answer

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.


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