Long-term stability of language with remapping in patients with medically refractory epilepsy

Electrical stimulation mapping is a widely used technique to determine functional localization for medically refractory epilepsy. Sites where stimulation interferes with naming are often focal regions of the frontal and temporal cortex. The extent to which these crucial sites remain in the same location over time in an individual adult patient has not yet been established. The aim of this study was to determine whether cortical naming sites identified using stimulation mapping are stable in their anatomical location over time in adult patients with medically refractory epilepsy.

Twenty-two patients who underwent electrical stimulation mapping for medically refractory epilepsy during surgical interventions separated by more than 1 year between 1967 and 2005 were included. A median of 8.35 years elapsed between mappings. The mean age at the first operation was 27.7 (range 10-39) years. Fourteen patients were female. Mapping occurred under two different conditions: intraoperatively in procedures conducted under local anesthesia or extraoperatively through implanted grid electrodes. A Bayesian hierarchical model of language site locations across repeated interventions was used to assess the stability of locations of stimulation-evoked interference in language naming.

Sites where electrical stimulation interferes with language naming were separated by a median of 0.6 cm between the 2 mappings. Eighty-six percent of the mapped sites related to language naming at the second operation were within 1.5 cm of a site identified at the first operation, 61% within 1 cm, and 36% within 0.5 cm. However, in 2 patients, none of the identified language naming sites at the second operation were within 1.5 cm of the sites from the first operation.

This unique, long-term series of neurosurgical mappings reveals that language naming sites in the cortex of adult patients with epilepsy show substantial long-term stability over many years. However, rare relocation of these sites does occur in some patients over many years.