Alternating hemiplegia of childhood: A rare neurological disorder with frequent temporary episodes of paralysis of one side of the body (hemiplegia) usually beginning before the age of 18 months. The eye movements, face, or limbs can be paralysed on either side of the body, but on only one side at a time. The cause is unknown. Abbreviated AHC. Also known as alternating hemiplegia syndrome.

One form of AHC has a favorable outlook. It occurs primarily at night, when a child awakens, and is apparently related to migraine. These children have no other mental or neurological impairments.

Another form of AHC is more serious and may include mental impairment, balance and gait difficulties, excessive sweating, changes in body temperature, and seizures. Treatment with flunarizine , a calcium channel blocker, may help to reduce the severity and duration of attacks of paralysis.