Alternating hemiplegia of childhood (AHC)
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A 6-month-old infant presents with recurrent episodes of hemiplegia that alternate sides. Episodes are triggered by stress, bathing, or temperature changes and resolve with sleep. Over time, the child develops developmental delay, dystonia, and epilepsy.
AD (usually de novo); ATP1A3 (Na+/K+ ATPase alpha-3 subunit)
- ~75% have ATP1A3 pathogenic variants
- Almost always de novo (recurrence risk is low)
- Allelic with rapid-onset dystonia-parkinsonism (RDP): same gene, different phenotype
- Onset before 18 months
- Recurrent episodes of hemiplegia that alternate sides (hallmark)
- Episodes resolve with sleep (characteristic)
- Triggers: stress, bathing, temperature changes, exertion
- Progressive developmental delay and intellectual disability
- Dystonia, choreoathetosis
- Epilepsy (develops in most patients)
- Episodic oculomotor abnormalities (nystagmus, strabismus)
- Clinical diagnosis based on characteristic episodes
- ATP1A3 gene testing
- EEG during episodes (may be normal, since episodes are not seizures)
- Brain MRI typically normal early, may show cerebellar atrophy later
- Flunarizine (calcium channel blocker): may reduce episode frequency and severity
- Avoidance of known triggers
- Prompt induction of sleep during episodes (can abort attacks)
- Antiepileptic drugs for seizures (episodes themselves are not epileptic)
AHC = Alternating + Hemiplegia + Childhood: the name is the diagnosis. Episodes alternate sides and present in childhood.
"ATP1A3 = A Terrible Pump": the Na+/K+ ATPase pump doesn't work properly, causing episodic neurological dysfunction.
"Sleep is the cure": episodes resolve with sleep, distinguishing AHC from most other causes of hemiplegia in children.