Abstracts

Rationale: Hypsarrhythmia is the characteristic EEG pattern associated with infantile spasms (West syndrome). It most commonly occurs between 4 and 12 months of age, but may rarely persist beyond, or even appear after the age of 12 months. This study describes those children with hypsarrhythmia after the age of 12 months.Methods: Patients older than 12 months of age with a hypsarrhythmic EEG were identified from the EEG database of this institution. Patient’s records from the previous 10 years were reviewed for clinical information including underlying aetiology, age of hypsarrythmia, seizure type(s), response to antiepileptic therapy and neuro-developmental outcome. Results: Forty patients (21 male) were identified. In 28 (70%), hypsarrhythmia was identified before, and persisted after the age of 12 months. The mean age at identification of hypsarrhythmia onset was 0.54 months. Twenty two of the 28 patients had pre-existing and severe neurological impairment including perinatal hypoxic ischaemic encephalopathy, Rett syndrome (CDKL5 mutation) and Aicardi syndrome. No cause was identified in six patients. In the remaining 12 patients, hypsarrhythmia was identified after the age of 12 months (mean, 47.7 and range, 15-96 months). Three patients continue to demonstrate hypsarrhythmia. All 12 patients had severe underlying neurological impairments. Two of the 40 patients had not experienced infantile or epileptic spasms. Conclusions: Rarely, hypsarrhythmia can occur after the age of 12 months. This study appeared to identify three groups; (1) patients with symptomatic West syndrome who continue to have a hypsarrhythmic EEG beyond 12 months of age; (2) patients with severe neurological impairment, but not necessarily infantile spasms, who develop hypsarrhythmia after the age of 12 months and (3) a smaller group with cryptogenic/presumed symptomatic West syndrome who have a hypsarrhythmic EEG and persisting spasms well beyond the first year of life.