Continuing medical education
Alopecia areata: Disease characteristics, clinical evaluation, and new perspectives on pathogenesis

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Alopecia areata (AA) is a common, inflammatory, nonscarring type of hair loss. Significant variations in the clinical presentation of AA have been observed, ranging from small, well-circumscribed patches of hair loss to a complete absence of body and scalp hair. Patients affected by AA encompass all age groups, sexes, and ethnicities, and may experience frustration with the unpredictable nature of their disease for which there is currently no definitive treatment. The cause of AA remains incompletely understood, though it is believed to result—at least in part—from a loss of immune privilege in the hair follicle, autoimmune-mediated hair follicle destruction, and the upregulation of inflammatory pathways. Patients with AA frequently experience marked impairment in psychological well-being, self-esteem, and may be more likely to suffer from psychiatric comorbidities. Part one of this two-part continuing medical education series describes the epidemiology, clinical evaluation, prognosis, and recent advancements in the understanding of the pathogenesis of AA.

Section snippets

Epidemiology

Key point

  1. Alopecia areata affects both sexes equally, affects patients of all ages, and is found in approximately 0.1% to 0.2% of the general population

Among the US population, the cumulative lifetime incidence of alopecia areata (AA) is estimated at 2%, while the prevalence is approximately 0.1% to 0.2%.1, 2 While AA affects both sexes equally, data from the Rochester Epidemiology Project revealed that men tended to be diagnosed earlier compared with women (mean age at diagnosis, 31.5 vs 36.2 years).2

Clinical evaluation

Key points

  1. Alopecia areata presents most commonly as well-demarcated patches of nonscarring, inflammatory hair loss that can progress to include all scalp or body hairs

  2. Exclamation point hairs, dystrophic hairs, and yellow dots are features of alopecia areata that can be identified with trichoscopy

  3. Nail abnormalities, such as regular pitting, brittleness, or striations, are seen in 10% to 20% of patients

AA most commonly presents as a sudden onset of focal well-circumscribed patches of hair loss on the scalp

Differential diagnosis

Key point

  1. Trichotillomania, temporal triangular alopecia, and telogen effluvium are the most important alternative diagnoses to consider

Trichotillomania can be challenging to differentiate from AA, and in some cases the two conditions may coexist. However, in trichotillomania, incomplete hair loss and a significant number of broken hairs will be observed on trichoscopy.16 Temporal triangular alopecia causes a circumscribed triangular-like area of nonscarring hair loss in the frontotemporal area. Patches

Clinical subtypes

Key point

  1. Several subtypes of alopecia areata have distinct presentations, including ophiasis, sisaipho, sudden graying type, and diffuse forms

Patients with the ophiasis subtype of AA (Fig 4) have band-like alopecia usually at the occipital hairline extending toward the temples, or rarely at the frontal hairline, that can be confused with frontal fibrosing alopecia.9 The sisaipho subtype occurs in the opposite distribution, causing hair loss centrally but sparing hairs at the margin of the scalp, and

Prognosis

Key points

  1. Younger age at initial presentation and severity at onset are the most important prognostic indicators

  2. Risk of progression from limited alopecia areata to alopecia totalis or alopecia universalis is approximately 5%

  3. The ophiasis subtype has a poorer prognosis and the acute diffuse and total alopecia subtype has a more favorable prognosis

Factors that may contribute to prognosis include AA subtype, extent of hair loss, duration of hair loss, age at onset, and family history.14 Approximately 5% of

Pathogenesis

Key points

  1. The anagen hair follicle is normally an immune privileged site, but this is disrupted in alopecia areata

  2. Inflammatory immune cells lead to dystrophic hair follicle cycling with premature entry into the telogen phase

The proximal portion of the anagen hair follicle (HF) constitutes an immune privileged site similar to the anterior chamber of the eyes, the pregnant uterus, and the testes.30, 31 This immune privilege appears to be disrupted in AA where an increase in major histocompatibility complex

Other factors contributing to alopecia areata

Key points

  1. Epigenetic mechanisms may affect susceptibility to alopecia areata

  2. Stress and diet may contribute to the development of alopecia areata

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    Funding sources: None.

    Dr Shapiro is a consultant for Aclaris Therapeutics, Applied Biology, Incyte, Replicel Life Sciences, and Samumed. Dr Christiano is a consultant for Aclaris Therapeutics and a principal investigator for Pfizer. The other authors have no conflicts of interest to declare.

    Ms Strazzulla and Dr Wang contributed equally to this article.

    Date of release: January 2018

    Expiration date: January 2021

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