Diagnostic Dilemma in an Infant With Sound-Triggered Motor Events: Reflex Epilepsy Versus Exaggerated Startle-A Case...

Auditory-triggered motor events in infancy present a significant diagnostic challenge due to overlap between epileptic and non-epileptic startle phenomena. We report the case of a term female infant with neonatal-onset seizures and subsequent development of reproducible sound-triggered jerky movements, raising diagnostic uncertainty between exaggerated startle reflex and reflex auditory epilepsy. The child initially presented with seizures on the third day of life and was treated with phenobarbital. During early infancy, brief motor events consistently precipitated by sudden auditory stimuli were observed, later accompanied by spontaneous seizures and developmental plateauing. Serial electroencephalography (EEG) revealed evolution from focal frontotemporal interictal epileptiform discharges to multifocal epileptiform activity with marked sleep activation, while repeated brain magnetic resonance imaging remained structurally normal. Over time, global developmental delay with hypotonia and impaired motor milestones became evident. The electroclinical trajectory suggested an evolving epileptic encephalopathy within the epileptic encephalopathy with spike-wave activation in sleep spectrum, despite the absence of a classic continuous spike-and-wave during sleep pattern. Whole-exome sequencing identified a homozygous HEXA gene variant of uncertain significance, without definitive biochemical or clinical evidence of GM2 gangliosidosis. The child was managed with multiple antiseizure medications and supportive neurodevelopmental interventions, resulting in partial seizure control but persistent developmental impairment. This case underscores the importance of longitudinal electroclinical correlation in infants with stimulus-triggered motor events and highlights that reproducible auditory-induced events with evolving epileptiform EEG abnormalities and developmental impact strongly favor reflex auditory epilepsy over non-epileptic exaggerated startle, even in the setting of normal neuroimaging and genetic uncertainty.