Clinical and histologic findings in temporal triangular alopecia.

Background: Temporal triangular alopecia (TTA; also called "congenital triangular alopecia") is a common disorder that is assumed to be congenital. Little is known about its histologic features.

Objective: Our purpose was to describe four new cases, review the literature, and present histologic features based on vertical and transverse sectioning.

Methods: The history, clinical features, and histologic findings of four patients with TTA are described and the relevant literature reviewed.

Results: Lesions of TTA are seldom congenital, and most are best described as lancet-shaped. The "bald spot" contains normal numbers of hairs, although virtually all are vellus or indeterminate follicles.

Conclusion: Most cases of TTA appear to develop during the first few years of life, and the designation "congenital" is a misnomer. The appearance of alopecia can be best explained as a focal zone of hair miniaturization leading to vellus hair formation.