Magnetoencephalographic study of posterior tibial nerve stimulation in patients with intracranial lesions around the central sulcus.

OBJECTIVE

To study interhemispheric differences of somatosensory evoked field (SEF) characteristics and the spatial distribution of equivalent current dipole sources in patients with unilateral hemispheric lesions around the central sulcus region.

METHODS

In 17 patients with perirolandic lesions, averaged somatosensory responses after posterior tibial nerve stimulation at the ankle were recorded with magnetoencephalography. Dipole source solutions in the affected (AH) and unaffected (UH) hemispheres were analyzed and compared for latency, equivalent current dipole strength, root mean square, and spatial distribution in relation to clinical findings.

RESULTS

Three main SEF components, P45m, N60m, and P75m, were identified in the hemisphere contralateral to the stimulated nerve. Dipole strength for the P45m component was significantly higher in the AH compared with the UH. SEF characteristics in the AH and UH showed no significant differences with respect to component latency or dipole strength of the N60m and P75m components. Interdipole location asymmetries exceeded 1.0 cm in 71% of the patients. Comparison of the posterior tibial nerve evoked responses (P45m and N60m) in patients with motor deficits and patients without deficits showed that these responses are enlarged in the AH when perirolandic lesions are present. Patients with motor deficits also showed an increased response for P45m in the UH.

CONCLUSION

The results of posterior tibial nerve SEFs suggest spatial and functional changes in the somatosensory network as a result of perirolandic lesions with a possible relationship with clinical symptoms. The results can provide further basis for the evaluation of cortical changes in the presence of perirolandic lesions.