Fibrosing alopecia in a pattern distribution is a primary lymphocytic cicatricial alopecia characterized by overlapping features of androgenetic alopecia and lichen planopilaris within an androgenetic pattern of hair loss. The androgenetic alopecia component is reflected histologically by follicular miniaturization, an increased proportion of vellus-type hairs, a reduced terminal-to-vellus hair ratio, and fibrous streamers. The lichen planopilaris component is characterized by lymphocyte-mediated injury of the upper follicle with perifollicular fibrosis, outer root sheath damage, loss of sebaceous glands, and eventual follicular destruction and scarring. In advanced or “burnt-out” lesions, the inflammatory infiltrate may be sparse, leaving predominantly perifollicular fibrosis and fibrosed follicular tracts. Clinically, the scarring alopecia follows a patterned distribution rather than the irregular multifocal distribution typical of classic lichen planopilaris.
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