Moyamoya disease is a rare condition in which the large arteries at the base of the brain slowly narrow, forcing tiny backup vessels to develop. These smaller vessels look like a “puff of smoke” on imaging, but they cannot carry enough blood, so the brain is starved of oxygen. Symptoms often start in childhood or early adulthood and can build up gradually or appear suddenly.

The earliest warning is usually repeated transient ischemic attacks (TIAs)—brief episodes of weakness, numbness, or trouble speaking that resolve within minutes to hours. Children may complain of a sudden weak arm or leg, slurred speech, or an odd facial droop that goes away quickly. Seizures are also common in kids and may be the first sign. Adults more often experience a full-blown ischemic stroke, with one-sided weakness, language problems, or vision loss that lasts longer than 24 hours. Headaches, especially migraine-like pain with flashing lights, can occur before or after attacks. Some people feel dizzy, have trouble balancing, or notice brief episodes of blurred or double vision.

When the tiny collateral vessels leak or rupture, bleeding into the brain can cause sudden severe headache, vomiting, stiff neck, or loss of consciousness. Because symptoms come and go early on, many patients are not evaluated until a major stroke or bleed occurs. Any repeated, unexplained neurologic event—especially in a young person—should prompt imaging of the brain vessels.