Alternating hemiplegia of childhood (AHC, MIM 104290) is a rare syndrome, characterised by early onset of episodic hemi- or quadriplegia lasting minutes to days. This disorder, first reported by Verret and Steel in 1971,¹ has historically been thought to represent a migraine equivalent¹ or an unusual form of epilepsy or a movement disorder,² as it typically presents with complex and variable clinical features.

In most patients, the earliest manifestations clearly related to AHC are tonic–dystonic attacks and paroxysmal nystagmus associated with autonomic changes and paroxysmal dyspnoea and usually appear between 3 and 6 months of age. The hemiplegic episodes develop before 18 months of age lasting anywhere from minutes to days at a time and involving either side of the body or shifting from one side to the other during the same episode with a period of bilateral weakness when the second side becomes involved.³

Some attacks are characterised by a bilateral involvement, which is apparent from the beginning, and do not follow an hemiplegic episode,³ which determines extreme hypotonia of the whole body with inability to move and a level of consciousness markedly depressed.

A characteristic feature of AHC is the disappearance of all abnormalities when the child falls asleep.³

With increasing age, hemiplegic episodes follow a general pattern of initially increasing frequency and duration, followed by a plateau, and finally by a decrease in the number and duration of attacks. Analogously, the paroxysmal manifestations associated with hemiplegia tend to decrease in frequency and intensity with time and usually disappear after 5–7 years. Development before the onset of hemiplegic episodes may be normal or delayed.

Epileptic seizures are reported in a variable percentage of sporadic patients.^3–5

An association with migraine has also been noticed since the earliest description.¹ Indeed, for …