What is alopecia areata?
Alopecia areata is an autoimmune condition affecting hair follicles causing hair loss. It typically presents with discrete bald patches on the scalp but can cause hair loss from all hair-bearing areas on the body.
Alopecia is a Latin term meaning hair loss, and areata refers to the patchy nature of the hair loss. The term alopecia areata is considered an umbrella term, which encompasses a number of variants including alopecia areata totalis or universalis, ophiasis, ophiasis inversus, and diffuse alopecia areata.
Who gets alopecia areata?
The lifetime risk of alopecia areata is approximately 2%. It affects children and adults of all skin and hair colours. Peak incidence occurs in the second and third decades and most patients experience onset before the fourth decade. Alopecia areata does not carry significant sex or ethnic predominance.
The following may increase the risk of alopecia areata:
- Chromosomal disorders such as Down syndrome
- Polyglandular autoimmune syndrome type 1
- Other autoimmune conditions such as vitiligo and thyroid disease
- A family history of alopecia areata
- Certain susceptibility genes (see below).
What causes alopecia areata?
A normal hair follicle cycles through multiple phases:
- Anagen is the active growth phase lasting one to eight years
- Catagen is a short involution phase lasting several weeks
- Telogen is the resting phase lasting several months
- Exogen is the shedding of the hair.
The exact mechanism responsible for hair loss in alopecia areata remains unclear. It is hypothesised that loss of immune privilege in anagen hair follicles plays a key role in the pathogenesis, and genetic susceptibility is also thought to contribute.
Immune privilege hypothesis
- Normal anagen hair follicles are thought to exhibit immune privilege, rendering them exempt from immune surveillance and protected against autoimmune attack.
- Protective immune privilege may be lost in alopecia areata, allowing hair follicle autoantigens to be presented to autoreactive CD8+ T cells.
- Subsequent autoimmune attack of the anagen follicle causes premature transition of the follicle into the telogen phase with ultimate loss of the hair.
This hypothesis is supported by the observation of a dense perifollicular infiltrate of T cells on histopathological examination of anagen follicles in alopecia areata; an area that is normally sparse of immune cells.
- Alopecia areata has a strong hereditary component.
- At least 16 genetic risk loci have been detected.
- Include numerous human leukocyte antigen (HLA) class I and II alleles, and several alleles of genes involved in immune pathways, hair pigmentation, and response to oxidative stress.
- Mode of inheritance appears to be complex, with environmental influences also at play.
What are the clinical features of alopecia areata?
Acute onset of hair loss may manifest in a number of patterns.
Patchy alopecia areata is the most common pattern, producing:
- Focal hair loss
- Well-demarcated single or several round/oval patches of normal-appearing skin.
The scalp is most commonly affected, but may also affect the:
- Any other hair-bearing areas.
Less common patterns include:
- Alopecia totalis – complete loss of scalp hair
- Affects up to 5% of patients with autoimmune hair loss
- Alopecia universalis – complete loss of body hair
- Affects less than 1%
- Ophiasis — bandlike hair loss on the occipital and temporal scalp margins
- Sisaipho (ophiasis inversus) — hair loss on the frontal, temporal, and parietal scalp which may mimic male pattern hair loss
- Diffuse alopecia areata (alopecia areata incognita) — rapid and widespread hair loss.
- Sudden greying — loss of pigmented hairs, resulting in the unmasking of existing grey hairs (“white overnight”).
Characteristic “exclamation point hairs” may be observed, particularly at the periphery of bald patches. An exclamation point hair is a broken strand with a relatively thick distal portion and thin proximal portion as it enters the scalp. They are the result of anagen arrest and cessation of hair shaft formation, with weakening and tapering of the shaft.
Some patients may experience localised tingling or itching preceding hair loss (trichodynia).
Upon regrowth, hairs may initially lack pigment and so grow back as white or blonde.
Nail changes can be seen in an estimated 10–40% of patients and tend to be associated with more severe disease.
- Nail pitting and ridging are most common.
- Other nail features include koilonychia, trachyonychia, Beau’s lines, onychorrhexis, onychomadesis, onycholysis, and red spots in the lunula.
How do clinical features vary in differing types of skin?
There are no differences in clinical features of alopecia in patients with skin of colour.
What are the complications of alopecia areata?
- Poor health-related quality of life due to distress.
- Higher rates of depression and generalised anxiety disorder; adjustment disorders are also common.
- Other autoimmune conditions may be more commonly observed in patients with alopecia areata e.g. thyroid disease, vitiligo, psoriasis, diabetes mellitus, and atopy.
How is alopecia areata diagnosed?
Alopecia areata is typically diagnosed on clinical features, however additional tests may aid diagnosis.
- Examination of the hair follicle, hair shaft, and scalp with a dermatoscope
- Features of active disease include exclamation point hairs, broken or dystrophic hairs, yellow dots and black dots.
- Hair pull test:
- Can help confirm hair loss and is often positive in alopecia areata
- Involves grasping 40–60 closely grouped hairs and applying gentle traction
- Positive when more than 10% of hairs are easily pulled out.
- Skin biopsy:
- May be required if diagnosis uncertain
- In acute alopecia areata, histopathology reveals a “bee-swarm pattern” of dense lymphocytic infiltrates surrounding anagen hair follicles
- Increase in catagen and telogen relative to anagen follicles, and follicle miniaturisation with progression of disease.
What is the differential diagnosis for alopecia areata?
- Temporal triangular alopecia
- Central centrifugal cicatricial alopecia
- Discoid lupus erythematosus affecting the scalp
- Tinea capitis
- Telogen effluvium (may mimic diffuse alopecia areata)
- Androgenetic alopecia (may mimic sisaipho pattern)
- Secondary syphilis (syphilitic alopecia)
- Lichen planopilaris
- Frontal fibrosing alopecia.
What is the treatment for alopecia areata?
There is no cure for alopecia areata. The hair loss in alopecia areata is associated with minimal harmful physical effects and spontaneous resolution may occur.
However, the psychological impact can be significant, therefore warranting treatment. Numerous therapies have been used with variable response and high quality evidence is lacking.
Treatments for mild alopecia areata (less than 50% scalp involvement)
Intralesional corticosteroid injections
- Injections of triamcinolone into areas of patchy alopecia of the scalp, beard, or eyebrow have an immunosuppressant effect and may speed up hair regrowth.
- Repeated four to six weekly and stopped once regrowth is complete.
- Potent corticosteroid solutions, creams, or ointments
- Most beneficial if used with occlusive dressings
- Minoxidil solution
- Ideally in combination with other therapies
- Anthralin (dithranol) cream or ointment
- Limited use in fair-haired individuals due to brown staining of skin and hair.
Treatments for extensive alopecia areata (greater than 50% scalp involvement, alopecia totalis, or universalis)
- Chemicals such as diphenylcyclopropenone are applied to affected areas to induce an allergic contact dermatitis, which may provoke hair regrowth.
- T-cells are theorised to be “distracted” from attacking hair follicles due to antigenic competition.
- Severe dermatitis, urticaria, lymphadenopathy, and depigmentation are potential side effects and may limit use.
- Generally reserved for short-term use in refractory or severe cases.
- Limited by well-known adverse effects.
- In June 2022, The FDA approved baricitinib use in severe alopecia areata.
- Clinical trials are ongoing, but preliminary results also show promise for other JAK inhibitors.
- JAK inhibitors block the T-cell-mediated inflammatory response that is thought to be responsible for damage to the hair follicle.
- Oral tofacitinib, baricitinib, and ruxolitinib seem to be more effective than topical preparations.
Improvement following numerous other less common and less studied treatments have been reported.
- Systemic examples include:
- Localised examples include:
Education and counselling
Patients should be informed that there is no cure and response to treatments are variable.
- Alopecia areata may spontaneously resolve, persist, relapse, and/or progress. Explaining the various possible disease courses can help manage expectations.
- Some patients may benefit from professional counselling to adjust to the appearance altering aspect of the disorder and regain self-confidence.
- Consider patient support groups.
Camouflaging hair loss can be helpful for patients who decide against pharmacological treatment or in those who have incomplete response.
- A prosthesis can be used to disguise scalp hair loss.
- Options include a full wig, hairpiece (clipped or glued to existing hair), or mesh integration system (custom made unit with hair extensions in the areas of alopecia).
- Styling products such as gels, mousses, powders, and sprays help to keep hair in place, achieve scalp coverage, and add volume.
- False eyelashes or artificial eyebrows
- Eyebrow tattooing or microblading can be helpful.
- Waterproof eyebrow pencil or eyeliner is a less permanent option.
How do you prevent alopecia areata?
We do not yet know how to prevent alopecia areata.
What is the outcome for alopecia areata?
Alopecia areata follows an unpredictable course. Spontaneous hair regrowth and recovery may occur and is common in some reports. Relapse is also common, however, and patients may have several phases of hair loss and subsequent regrowth. The risk of progression to alopecia totalis or alopecia universalis is approximately 5–10%, from which recovery is unlikely.
Response to treatment is highly variable and hair loss may recur when therapy is stopped.
Poor prognostic factors include:
- Younger age at onset
- More extensive disease
- Hair loss of greater than one-year duration
- Nail dystrophy
- Ophiasis pattern
- Family history of alopecia areata
- Presence of atopy or other autoimmune diseases.