Histologic features of alopecia areata other than peribulbar lymphocytic infiltrates

Histologic features other than a lymphocytic infiltrate around follicular bulbs are now recognized as helpful clues to the diagnosis of alopecia areata, especially in long-standing lesions where the peribulbar lymphocytic infiltrate may be sparse or absent.

We sought to determine the frequency of peribulbar lymphocytic infiltrates, eosinophils, lymphocytes, and melanin in fibrous tracts, pigment casts in follicles, the presence of catagen/telogen follicles, follicular miniaturization, and dystrophic ("nanogen") follicles in alopecia areata. Secondly, we sought to compare the diagnostic use of transversely sectioned versus horizontally sectioned specimens in those cases for which both were available (15 of 109 cases).

The pathology archives of Geisinger Medical Center (Danville, PA), Wilford Hall US Air Force Medical Center (San Antonio, TX), and Brooke US Army Medical Center (San Antonio, TX) were searched for the term "alopecia areata" in the diagnostic field from the period of 1991 to 2006, which yielded 109 cases with sections suitable for review. Cases from the two military institutions from 1997 or earlier were excluded to avoid any overlap with data previously reported by our group.

A peribulbar lymphocytic infiltrate was present in 92 specimens (84%), eosinophils in fibrous tracts in 48 (44%), lymphocytes in fibrous tracts in 102 (94%), melanin within fibrous tracts in 92 (84%), pigment casts within follicular canals in 46 (44%), catagen follicles in 101 (93%), and miniaturized follicles in 98 (90%). Dystrophic miniaturized follicles were rare (4 cases). In 14 of 15 cases with both vertical and transverse sections, either was diagnostic. One case showed diagnostic features only in vertical sections.

Comparable vertical and transverse sections were only available for a limited number of the cases. We did not correlate duration of disease with individual findings. Our results were correlated with the clinical diagnosis but not with serologic tests for syphilis.

Although most specimens showed evidence of a peribulbar lymphocytic infiltrate (84%), a higher percentage showed evidence of follicles in catagen/telogen phase (93%) and evidence of miniaturization of follicles (90%). This could lead to an incorrect diagnosis of trichotillomania or pattern alopecia. Pigment casts within the hair canal were also found in a significant number of follicles, especially in catagen follicles, creating further potential for misdiagnosis as trichotillomania. A significant percentage showed evidence of eosinophils (44%), melanin (84%), and lymphocytes (94%) in fibrous tracts. These features are particularly helpful when a peribulbar lymphocytic infiltrate is lacking. Vertical and transverse sections appear comparable.