title: Alopecia areata update: part I. Clinical picture, histopathology, and pathogenesis.
abstract: Alopecia areata (AA) is an autoimmune disease that presents as nonscarring hair loss, although the exact pathogenesis of the disease remains to be clarified. Disease prevalence rates from 0.1% to 0.2% have been estimated for the United States. AA can affect any hair-bearing area. It often presents as well demarcated patches of nonscarring alopecia on skin of overtly normal appearance. Recently, newer clinical variants have been described. The presence of AA is associated with a higher frequency of other autoimmune diseases. Controversially, there may also be increased psychiatric morbidity in patients with AA. Although some AA features are known poor prognostic signs, the course of the disease is unpredictable and the response to treatment can be variable. Part one of this two-part series on AA describes the clinical presentation and the associated histopathologic picture. It also proposes a hypothesis for AA development based on the most recent knowledge of disease pathogenesis.
  
  
  OBJECTIVE
  After completing this learning activity, participants should be familiar with the most recent advances in AA pathogenesis, recognize the rare and recently described variants of AA, and be able to distinguish between different histopathologic stages of AA.
authors.affiliation: Department of Dermatology and Skin Science, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Abdullah
authors.initials: A
authors.lastname: Alkhalifah
authors.forename: Adel
authors.initials: A
authors.lastname: Alsantali
authors.forename: Eddy
authors.initials: E
authors.lastname: Wang
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: McElwee
authors.forename: Jerry
authors.initials: J
authors.lastname: Shapiro
mesh_terms: D000328:Adult; D000506:Alopecia Areata / Q000150:complications / Q000209:etiology* / Q000473:pathology; D000818:Animals; D001327:Autoimmune Diseases / Q000209:etiology* / Q000473:pathology; D002648:Child; D004195:Disease Models, Animal; D005260:Female; D018859:Hair Follicle / Q000276:immunology / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D009260:Nail Diseases / Q000209:etiology; D051381:Rats