Continuing medical educationAlopecia areata: Disease characteristics, clinical evaluation, and new perspectives on pathogenesis
Section snippets
Epidemiology
Key point 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 Alopecia areata presents most commonly as well-demarcated patches of nonscarring, inflammatory hair loss that can progress to include all scalp or body hairs Exclamation point hairs, dystrophic hairs, and yellow dots are features of alopecia areata that can be identified with trichoscopy 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 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 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 Younger age at initial presentation and severity at onset are the most important prognostic indicators Risk of progression from limited alopecia areata to alopecia totalis or alopecia universalis is approximately 5% 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 The anagen hair follicle is normally an immune privileged site, but this is disrupted in alopecia areata 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 Epigenetic mechanisms may affect susceptibility to alopecia areata Stress and diet may contribute to the development of alopecia areata
References (89)
- et al.
Lifetime incidence risk of alopecia areata estimated at 2.1 percent by Rochester Epidemiology Project, 1990–2009
J Invest Dermatol
(2014) - et al.
Alopecia areata update
J Am Acad Dermatol
(2000) - et al.
The role of scalp dermoscopy in the diagnosis of alopecia areata incognita
J Am Acad Dermatol
(2008) - et al.
Videodermoscopy in the evaluation of hair and scalp disorders
J Am Acad Dermatol
(2006) - et al.
Alopecia areata investigational assessment guidelines–part II
J Am Acad Dermatol
(2004) - et al.
SALT II: a new take on the Severity of Alopecia Tool (SALT) for determining percentage scalp hair loss
J Am Acad Dermatol
(2016) - et al.
Clinical and trichoscopic characteristics of temporal triangular alopecia: a multicenter study
J Am Acad Dermatol
(2016) - et al.
Clinical and histologic findings in temporal triangular alopecia
J Am Acad Dermatol
(1994) - et al.
Acute diffuse and total alopecia: a new subtype of alopecia areata with a favorable prognosis
J Am Acad Dermatol
(2009) - et al.
Incidence of alopecia areata in Olmsted County, Minnesota, 1975 through 1989
Mayo Clin Proc
(1995)
Alopecia areata: a long term follow-up study of 191 patients
J Am Acad Dermatol
Alopecia areata: a statistical study and consideration of endocrine influences
J Invest Dermatol
Immune privilege in hair growth
J Invest Dermatol
A ‘hairy’privilege
Trends Immunol
Molecular signatures define alopecia areata subtypes and transcriptional biomarkers
EBioMedicine
Identification of autoantigen epitopes in alopecia areata
J Invest Dermatol
Alopecia areata in aging C3H/HeJ mice
J Invest Dermatol
A new humanized mouse model for alopecia areata
J Investig Dermatol Symp Proc
Experimental induction of alopecia areata-like hair loss in C3H/HeJ mice using full-thickness skin grafts
J Invest Dermatol
Transfer of CD8(+) cells induces localized hair loss whereas CD4(+)/CD25(-) cells promote systemic alopecia areata and CD4(+)/CD25(+) cells blockade disease onset in the C3H/HeJ mouse model
J Invest Dermatol
Treatment of alopecia areata with anti-interferon-γ antibodies
J Invest Dermatol Symp Proc
Structural abnormalities of the hair shaft
J Am Acad Dermatol
Genomewide scan for linkage reveals evidence of several susceptibility loci for alopecia areata
Am J Hum Genet
Interleukin-21 as a new therapeutic target for immune-mediated diseases
Trends Pharmacol Sci
MHC class I expression in murine skin: developmentally controlled and strikingly restricted intraepithelial expression during hair follicle morphogenesis and cycling, and response to cytokine treatment in vivo
J Invest Dermatol
Maintenance of hair follicle immune privilege is linked to prevention of NK cell attack
J Invest Dermatol
Alopecia areata induced in C3H/HeJ mice by interferon-gamma: evidence for loss of immune privilege
J Invest Dermatol
History of atopy or autoimmunity increases risk of alopecia areata
J Am Acad Dermatol
Comorbidity profiles among patients with alopecia areata: the importance of onset age, a nationwide population-based study
J Am Acad Dermatol
Cardiovascular risk in patients with alopecia areata (AA): a propensity-matched retrospective analysis
J Am Acad Dermatol
Cardiac manifestations of systemic lupus erythematosus
Rheum Dis Clin North Am
Concordance rate of alopecia areata in identical twins supports both genetic and environmental factors
J Am Acad Dermatol
Development of alopecia areata is associated with higher central and peripheral hypothalamic–pituitary–adrenal tone in the skin graft induced C3H/HeJ mouse model
J Invest Dermatol
A healthy gastrointestinal microbiome is dependent on dietary diversity
Mol Metabol
Prevalence of alopecia areata in the first National Health and Nutrition Examination Survey
Arch Dermatol
Profile of alopecia areata: a questionnaire analysis of patient and family
Int J Dermatol
Alopecia areata: an evaluation of 736 patients
Arch Dermatol
The pattern and profile of alopecia areata in Singapore–a study of 219 Asians
Int J Dermatol
Alopecia areata prevalence by gender and age
J Eur Acad Dermatol Venereol
Management of alopecia areata
BMJ
Alopecia areata: clinical presentation, diagnosis, and unusual cases
Dermatol Ther
Guidelines for the management of alopecia areata
Br J Dermatol
Profile of alopecia areata in Northern India
Int J Dermatol
British Association of Dermatologists’ guidelines for the management of alopecia areata 2012
Br J Dermatol
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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