Ictal MEG yield in patients with drug refractory epilepsy undergoing magnetoencephalography

Background: It is not uncommon for a person with epilepsy (PWE) who is referred for a magnetoencephalography to have a seizure during the procedure. The aim of this study was to investigate evidence of focal dipole clustering in patients who happened to have seizures during MEG acquisitions.

Objective:

1. To compare the source localization results of ictal and inter-ictal MEG studies.

2. To evaluate the efficacy of MEG results, both Inter-ictal and Ictal with scalp video EEG And MRI findings.

Methods: We analysed prospectively average 2 h inter-ictal MEG data of PWE acquisition with equivalent current dipole (ECD) model with both DANA and CURRY analysis softwares, of the patients with DRE referred to MEG Facility of AIIMSNBRC Center of Excellence Epilepsy (COE) for MEG assessment. The inter-ictal and ictal MEG was analysed in DANA as well as CURRY by different technologists and epileptologists blinded to each other's results.

Results: 30 out of 310 patients having drug refractory epilepsy who underwent MEG study (Elekta Neuromag^® TRIUX^TM 306 Channel) had seizures during acquisition. Most seizures were focal (25), however 5 patients had secondarily generalized seizures. Their inter-ictal data analysis showed preliminary abnormal findings in the form of either spikes, sharps or slow waves. Inter-ictal source analysis made with equivalent current dipole model showed focal clustering in 24/30 patients who got convulsions during acquisition. Ictal finding were concordant with the MRI in 85% of those with an abnormal MRI substrate. In those with a substrate negative MRI (9) ictal MEG was concordant with the ictal onset zone on scalp EEG in 56%. In these a repeat MEG done in 2 was again consistent to that of the previous MEG cluster. Interictal and ictal MEG were convergent in their clusters to about 68%.

Findings:

Total no. of patients	310
No of patients who got convulsions	30
No of patients with focal clustering of interictal discharges	24/30
No of patients who got secondary generalized seizures	5
Abnormal MRI	21/30	Ictal finding concordant with MRI findings	18/21 (85%)
Ictal finding concordant with Interictal EEG findings	17/30 (56%)
No. of MEG clustering consistent with repeat MEG	2/2 (100%)
Interictal and Ictal MEG convergence	14/21 (68%)

Conclusion: This ictal analysis study in PWE who are drug refractory and happen to have seizures during acquisitions, have evidence to show that focal clustering region corresponds to the same area as indicated by the other complimentary tests.

 

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