Alopecia areata is sudden patchy hair loss in people with no obvious skin or systemic disorder. It is thought to be a T-cell-mediated autoimmune disease affecting genetically susceptible people. Occasionally, it coexists with autoimmune vitiligo or thyroiditis, such as Hashimoto’s thyroiditis.
Diagnosis is by inspection. Alopecia areata typically manifests as discrete circular patches of hair loss characterised by short broken hairs at the margins, resembling exclamation points. Measures of thyroid-stimulating hormone, vitamin B12, and autoantibodies are indicated only when coexisting autoimmune disease is suspected.