Aspiration pneumonia is common in this population and results in frequent hospitalization. Typically, the onset of these disorders is during the first 3 years of life. This is less frequent than the idiopathic variety, and the age of onset is usually between a few months to 2-3 years. Clinical features include psychomotor retardation, and neuroimaging frequently demonstrates brain atrophy. Myoclonic jerks can occur alone, but they more commonly are associated with generalized clonic seizures.
Rhythmic jerks can occur during sleep, with associated dystonic posturing during wakefulness.
The prognosis for meaningful cognitive function is poor, although the myoclonic jerks may be medically controlled. This group includes all idiopathic cases that primarily display recurrent myoclonic attacks. Some patients may have infrequent generalized tonic-clonic seizures. Most myoclonic seizures are axial, which sometimes results in falls. The outcome in these patients is usually favorable, although about half the patients may have behavioral or cognitive dysfunction.