Olfactory epileptic auras

Abstract

Background: Olfactory epileptic auras are rare, constituting about 0.9% of all auras, and are typically described as unpleasant. They have usually been associated with tumors, but in some recent studies they have not.

Methods: We identified 13 patients (7 male, 6 female) with olfactory epileptic auras from 1423 patients with partial epilepsy evaluated for intractable seizures between 1991 and 1996. All had routine EEGs and MRI. Twelve underwent prolonged video-EEG monitoring.

Results: Olfactory sensations were of various types but unpleasant in only seven. Auras evolved to complex partial seizures (automotor, hypermotor, or dialeptic seizures) in 12 patients, with further evolution to generalized tonic-clonic seizures in three and aphasic seizures in one patient. The EEG focus was localized to the mesial temporal region in all. Ten patients had a mesial temporal tumor; in one patient, it extended to the superior temporal gyrus, and in another, the frontal lobe. The tumor involved only the amygdala in two patients and both amygdala and hippocampus in six; none had hippocampal involvement alone. Surgery was performed in nine patients. All except one with partial tumor resection had a seizure-free outcome. This patient also became seizure-free after repeat surgery to remove residual tumor tissue in the amygdala.

Conclusions: Olfactory auras are not necessarily unpleasant. The amygdala is the most likely symptomatogenic zone of olfactory auras. Tumors are the commonest etiology; mesial temporal sclerosis is a relatively rare cause.