Lateralizing value of the auditory aura in partial seizures.

PURPOSE

To describe the semiological features of auditory aura and to assess their possible lateralizing value in partial epilepsy.

METHODS

Out of a series of 8,000 patients with epilepsy, we investigated 121 cases with partial seizures in whom auditory features were the first ictal symptom. According to the dominant type of aura, patients were divided into four subgroups-1A (67 cases), 1B (22 cases), 2A (14 cases), and 2B (18 cases)-corresponding to the presence of simple or complex hallucinations and positive or negative illusions, respectively. The side of the epileptic zone (EZ) was defined based on available data: surgical/presurgical study or presence of a neuroradiological lesion, corresponding interictal epileptiform EEG and ictal semiology (level 1); a left EZ was also hypothesized in right-handed patients with ictal aphasia plus a left neuroradiological lesion or a left interictal EEG focus (level 2).

RESULTS

Forty-five patients (37%) described the aura as unilateral. The side of epileptogenic zone (EZ) was definable in 36 patients (level 1: 24; level 2: 12). Overall, a unilateral auditory aura was contralateral to the EZ in half of the cases (8/16), but always contralateral in patients studied for presurgical evaluation (4/4). Simple hallucinations lateralized seizure onset on the right side in nine cases, on the left in 12. Among 1B patients (either musical and verbal contents), the EZ was on the left side in all cases (5/5). Positive illusions were associated with right foci in two cases, and left foci in two. Negative illusions always lateralized seizure onset to the dominant hemisphere (6/6).

CONCLUSIONS

Auditory aura is a rare symptom in partial epilepsy. The perception of the auditory sensation referred to one ear is not a unique lateralizing sign for the contralateral temporal neocortex. Complex hallucinations with verbal content and negative illusion may lateralize seizure onset in the dominant hemisphere. The role of laterality for musical hallucinations remains unclear as it depends on individual musical ability and hemispheric dominance for music.