Confirmation of infantile spasms resolution by prolonged outpatient EEGs

OBJECTIVE: There is no consensus on the type or duration of the posttreatment EEG needed for assessing treatment response for infantile spasms (IS). We assessed whether outpatient electroencephalograms (EEGs) are sufficient to confirm infantile spasms (IS) treatment response. METHODS: Three‐year retrospective review identified new‐onset IS patients. Only presumed responder to IS treatment at 2 weeks with a prolonged (>90 minutes) outpatient EEG to assess treatment response and at least 3‐month follow‐up were included. Hypsarrhythmia, electroclinical spasms, and sleep were evaluated for the first hour and for the duration of the EEG. RESULTS: We included 37 consecutive patients with new‐onset IS and presumed clinical response at 2 weeks posttreatment. Follow‐up outpatient prolonged EEGs (median: 150 minutes, range: 90‐240 minutes) were obtained 14 days (IQR: 13‐17) after treatment initiation. EEGs detected ongoing IS in 11 of 37 (30%) presumed early responders. Prolonged outpatient EEG had a sensitivity of 85% (confidence interval [CI] 55%‐98%) for detecting treatment failure. When hypsarrhythmia and/or electroclinical spasms were not seen, EEG had a negative predictive value 92% (CI: 75%‐99%) for confirming continued IS resolution. Outpatient EEG combined with clinical assessment, however, identified all treatment failures at 2 weeks. Compared with the entire prolonged EEG, the first‐hour recording missed IS in 45% (5/11). While sleep was captured in 95% (35/37) of the full EEG recording, the first hour of recording captured sleep in only 54% (20/37). SIGNIFICANCE: Infantile spasms treatment response can be confirmed with a clinical history of spasm freedom and an outpatient prolonged EEG without evidence for ongoing spasms (hypsarrhythmia/electroclinical spams on EEG). Outpatient prolonged EEG, but not routine EEGs, represents an alternative to inpatient long‐term monitoring for IS posttreatment EEG follow‐up.