gms | German Medical Science

Objective: Plastic changes of cortical functional anatomy are a frequent phenomenon not only in pathological conditions but also in healthy subjects. The current study aims at establishing a reliable and objective way to measure cortical plastic changes of the motor areas using navigated TMS.

Method: For this pilot study 5 patients with gliomas in the immediate vicinity of the precentral gyrus and subsequent motor deficit were examined before surgery and 12 months after surgery with nTMS. We calculated the Hotspot and Center of Gravity (COG) for the FDI muscle. Using the MEP responses at 105% RMT a weighted map of cortical motor function was created for both hemispheres. Accordingly 5 healthy subjects were examined.

Results: nTMS depicted the Hotspot and COG for the examined muscles for both patients and volunteers at the baseline examination. At follow-up, the pattern of cortical motor representation showed significant variation from the baseline examination in both groups: COG in volunteers (11.9 mm ± 5.7) and COG in patients (54.0 mm ± 25.3). In the healthy subjects the area of the cortical FDI muscle representation remained near baseline calculations at follow-up, whereas in patients significantly greater divergence from baseline calculations was observed. Further analysis revealed an expansion of motor cortical representation on the tumor hemisphere (+22% ± 35.5) and a decrease (-96% ± 31.0) on the healthy hemisphere indicating a bihemispheric cortical reorganisation.

Conclusions: nTMS enables a detailed evaluation of the individual dynamics of ongoing cortical reorganization. Potential clinical implications are discussed.