A 26-year-old woman is evaluated for headaches, which began when she was 14 years old. She states that she initially sees bright zig-zag bands, which expand in the shape of a horseshoe in her right visual field. Twenty minutes later, she develops a throbbing headache over the left frontal area, associated with photophobia and nausea. The headaches last 1–3 days and they occur once a month. There is no medical history, and she takes only multivitamin supplements. Her sister has been diagnosed with migraines. Her examination is normal, including equal and reactive pupils, full extraocular movements, and normal strength and sensation. A magnetic resonance scan of the brain shows no abnormalities.