Alopecia areata

Alopecia areata (AA) is a common autoimmune, non-scarring hair loss disorder characterized by sudden, patchy hair loss that is often reversible. It typically presents with circular bald patches due to immune-mediated attack on hair follicles, but follicles remain intact, allowing potential regrowth. It may affect hair on the scalp or any hair-bearing area.

AA occurs in all genders and ages, with a lifetime incidence around 2%. Prevalence appears to be rising due to increased awareness and better diagnostic practices. Typical onset occurs between 15–30 years, and prevalence is slightly higher in children than adults.

• By extent: Patchy AA, Alopecia totalis (scalp hair loss), Alopecia universalis (total body hair loss).
• Severity of Alopecia Tool (SALT): S0=no loss, S1=≤25%, S2=26–50%, S3=51–75%, S4=76–99%, S5=100%.
• Patterns: Patchy, ophiasis (scalp periphery), sisaipho (central scalp), diffuse.
   

AA is a T-cell–mediated autoimmune disease targeting anagen-stage hair follicles. Immune privilege collapse leads to follicular attack by CD4+/CD8+ T cells (NKG2D+), mediated by IFN-γ, IL-17 cytokines. Melanocyte-associated autoantigens may trigger responses. Genetic associations: TRAF1/C5, HLA class II, PTPN22, CTLA4 genes.

Associated conditions: autoimmune thyroid disease (13–20%), vitiligo, diabetes mellitus type 1, atopic dermatitis, asthma. Environmental triggers: stress, infections (EBV, hepatitis, influenza), vaccinations (COVID-19).
 

Hallmark: Sudden patchy non-scarring hair loss. Exclamation mark hairs (proximal thinning hair shart) and upon breaking off black dots commonly seen on dermoscopy. Also yellow dots except when long-standing AA and sebaceous atrophy. Hair pull test positive during active shedding. Special patterns: ophiasis, sisaipho, diffuse, incognita. Nail changes: pitting, trachyonychia, Beau’s lines. Body hair involvement: beard, eyebrows, eyelashes.

Primarily clinical, supported by dermoscopy: exclamation mark hairs, black dots, yellow dots. Scalp biopsy rarely needed ("swarm of bees" infiltrate, follicular Swiss cheese pattern). Laboratory: screen for thyroid dysfunction, vitamin D levels as indicated.

Primarily scalp (90%); also beard, eyebrows, eyelashes, body hair.

Assess rapidity of onset, triggers (stress, illness, vaccination), family and personal autoimmune/atopic history.

Characteristic lymphocytic infiltrate ("swarm of bees"), pigment incontinence, follicular Swiss cheese pattern.

Mainly psychosocial distress, reduced quality of life; secondary sunburn risk, eye irritation from eyelash loss.

No proven prophylaxis; stress management advised.

Unpredictable; spontaneous regrowth common (30–50% within 6–12 months). Poorer prognosis: extensive involvement, young onset, nail changes, autoimmune associations. High relapse rate.

1. King B et al. Two Phase 3 Trials of Baricitinib for Alopecia Areata (BRAVE-AA1 and BRAVE-AA2). New England Journal of Medicine. 2022;386(18):1687–1699.
2. FDA. FDA Approves Pfizer’s Litfulo (Ritlecitinib) for Adults and Adolescents With Severe Alopecia Areata. FDA Press release; June 23, 2023.
3. FDA. U.S. FDA Approves Leqselvi (Deuruxolitinib), an Oral JAK Inhibitor for the Treatment of Severe Alopecia Areata. FDA Press release; July 25, 2024.
4. Yahya A et al. JAK inhibitors for alopecia areata: a systematic review and meta-analysis. Annals of Medicine and Surgery. 2022.
5. Sibbald C et al. Alopecia areata: An updated review for 2023. Skin Therapy Letter. 2023.
6. Vinod M et al. Efficacy and safety of ritlecitinib in adolescents with alopecia areata through 48 weeks. Journal of the American Academy of Dermatology. 2023.
7. Mackay-Wiggan J et al. Long-term follow-up of tofacitinib treatment in alopecia areata. JCI Insight. 2023.
8. Lee HH et al. Epidemiology of alopecia areata: lifetime prevalence and incidence update. Journal of the American Academy of Dermatology. 2023.
9. Gilhar A et al. Melanocyte-associated autoantigens in Alopecia Areata pathogenesis. Journal of Investigative Dermatology. 2023.
10. Petukhova L et al. Genetic markers of Alopecia Areata: PTPN22, CTLA4 and others. Nature. 2023.