Alopecia Areata
On this page
Direct answer
Alopecia areata is an autoimmune disorder in which T lymphocytes, mainly CD8-positive cells, attack anagen hair follicles and cause non-scarring patchy hair loss. Its hallmark is the exclamation mark hair, a broken hair that is narrow at the scalp end and thicker at the tip, and nail pitting is often associated. Treatment ranges from observation for small patches to intralesional steroids, with JAK inhibitors reserved for extensive disease.
What you must remember
- Pathogenesis: CD8-positive T cells and interferon-gamma target the anagen bulb in genetically predisposed people, after loss of immune privilege.
- Exclamation mark hair: a short, broken hair, narrow at the base and thicker towards the tip, seen at the margins of active patches.
- Nail changes: fine regular pitting, trachyonychia and red spots in the lunula, which signal nail matrix involvement.
- Patterns: patch disease, ophiasis (band-like loss at the occipital margin), alopecia totalis (whole scalp) and alopecia universalis (whole body).
- Associations: atopy, autoimmune thyroid disease, vitiligo and Down syndrome.
- Histology: a peribulbar lymphocytic infiltrate, classically described as a swarm of bees around anagen bulbs.
- Prognosis: many small patches regrow, whereas extensive disease, ophiasis and nail changes predict a more difficult course.
- Intralesional therapy: triamcinolone acetonide is the standard intralesional steroid for limited patch disease.
A treatment ladder for alopecia areata
A 22-year-old woman has three coin-sized bald patches on the scalp with exclamation mark hairs at their edges. Treatment is chosen by the extent of hair loss, the pattern and the duration of disease.
- Confirm active disease: Exclamation mark hairs on trichoscopy or a positive pull test confirm active alopecia areata, and biopsy is reserved for atypical cases.
- Assess the extent: Estimate the percentage of scalp loss, and look for ophiasis, totality or nail involvement, since these guide the next step.
- Observe small patches: Limited single patches often regrow spontaneously, so reassurance and observation are reasonable for a defined period.
- Use intralesional steroids: Triamcinolone acetonide is injected into the active edge of patches at dilute concentrations and repeated intervals, which limits the risk of atrophy.
- Add topical and systemic options: Potent topical steroids, minoxidil and topical immunotherapy with diphencyprone or squaric acid dibutylester are used, while systemic corticosteroids are reserved for rapidly progressive disease.
- Consider JAK inhibitors: Agents such as baricitinib are used for severe or extensive disease under specialist supervision, with monitoring for infection and laboratory changes.
Where the exam tries to catch you
Alopecia areata questions test the hair signs, the prognosis and the correct order of treatment.
- Trap: mistaking exclamation mark hairs for traction alopecia or telogen effluvium. Correct: tapered, broken shafts at the edge of a patch are characteristic of active alopecia areata, whereas traction breaks at the scalp margin and telogen effluvium lacks such shafts.
- Trap: treating extensive alopecia areata with minoxidil alone. Correct: minoxidil is only an adjunct, and extensive disease needs immunomodulatory therapy.
- Trap: assuming alopecia areata is always reversible. Correct: alopecia totalis and universalis, ophiasis and nail changes carry a poorer prognosis and a higher risk of recurrence.
Frequently asked questions
What is the exclamation mark hair in alopecia areata?
Exclamation mark hairs are short, broken hairs that are narrow at the scalp end and thicker towards the broken tip, and they are seen at the edges of active alopecia areata patches. They reflect damage to the anagen hair shaft and are a supportive clinical sign.
Which nail changes are associated with alopecia areata?
Fine regular pitting, trachyonychia with a sandpaper-like surface and red spots in the lunula are associated with alopecia areata. Nail involvement is linked with more extensive or longer-standing disease, and it is often used to judge prognosis.
Which intralesional steroid is used in alopecia areata?
Triamcinolone acetonide is the standard intralesional steroid for alopecia areata, given into the active edge of patches. Dilute concentrations injected at repeated intervals reduce the risk of skin atrophy compared with stronger preparations.
Why are JAK inhibitors used in alopecia areata?
JAK inhibitors block the cytokine signalling, including interferon-gamma, that drives the immune attack on hair follicles. They are used for severe or extensive alopecia areata under specialist supervision, given their need for monitoring of infection risk and laboratory parameters.