Olfactory sensory phenomena as the main seizure type in a child with low-grade glioma: a case report

Olfactory sensory phenomena (OSP) are a rare and often underrecognized descriptor of seizures without observable clinical manifestations, particularly in children. We report a case involving a 7-year and 9-month-old boy who experienced OSP as the sole seizure manifestation for nearly a year, resulting in a delayed diagnosis. Symptoms were initially misattributed to gastroesophageal reflux but gradually progressed to include focal impaired consciousness seizures. Brain magnetic resonance imaging revealed a mass lesion involving the right optic nerve, hypothalamus, and medial temporal lobe, leading to the diagnosis of focal epilepsy owing to a structural etiology. Histopathological assessment confirmed a low-grade glioma (LGG). Because OSP persisted despite lacosamide therapy, perampanel (PER) was introduced based on prior reports of its efficacy in epilepsy associated with glioma; however, instead of reducing, the OSP frequency increased after PER initiation. This case highlights the diagnostic challenge posed by nonmotor seizures with subtle clinical presentations and underscores the importance of considering epilepsy in patients with recurrent, unexplained sensory symptoms such as abnormal smells or nausea. It also contributes to the limited literature on pediatric focal epilepsy associated with LGG, providing educational value for physicians less familiar with atypical seizure semiology.