The Utility of the Hypsarrhythmia Paroxysm Index and Sleep Spindles in EEG for Predicting Cognitive Outcomes in a Case Series of Infantile Spasms

Objectives: Among patients with West Syndrome (WS), the underlying brain dysfunction is considered to be the major determinant of cognitive outcome. However, regardless of whether the WS type is symptomatic or cryptogenic, patients with infantile spasms may have a favourable or grim prognosis. The purpose of this study was to utilize electroencephalography (EEG) to guide treatment, and to assess cognitive outcome. Methods: We retrospectively reviewed the clinical and sleep EEG data in 16 patients who received adrenocorticotropic hormonal therapy between 2002 and 2014. The hypsarrhythmia paroxysm index (HPI), the frequency or duration of hypsarrhythmia paroxysms in non-rapid eye movement (NREM) sleep, and sleep spindles were evaluated in groups constituted according to etiology. Results: Cryptogenic patients whose onset of spasms began after 3 months of age and who experienced a shorter treatment delay had preserved spindles and favourable cognitive outcomes. Sleep spindles disappeared in cryptogenic patients with an early onset of spasms, long treatment delay, and high HPI at referral; their neurodevelopmental prognosis was unfavourable. In symptomatic cases in which the age of onset of spasms was earlier than 3 months and there had been a short treatment delay, sleep spindles never fully evolved, and the prognosis was poor. Patients with corpus callosum hypogenesis, a relatively mild malformation, had high HPI values at referral. While two of these patients did not display spindles during the follow-up, three had reappearing spindles as HPI values diminished, and the outcome was less severe in these patients. Conclusion: This study highlights the significance of EEG in studies of the prognosis of infantile spasms and demonstrates an objective approach that utilizes concurrent evaluation of sleep spindles and HPI.