gms | German Medical Science

Objective: In patients with cervical stenosis, functional impairment of the motor pathways is traditionally measured by determination of motor and sensory evoked potentials. The current study aims at establishing a reliable and objective way to measure corticospinal excitability and plastic changes of the motor area in patients with cervical myelopathy using navigated TMS.

Method: For this pilot study 18 patients with a cervical myelopathy due to cervical spinal canal stenosis were examined preoperatively with nTMS as well as in a 9 months follow-up. On the basis of the initial JOA score two patient groups were established (JOA<12/>12). We determined the resting motor threshold, recruitment curve and cortical silent period for the FDI muscle. Using the MEP responses at 105% RMT a weighted map of cortical motor function was created for both hemispheres. Accordingly 8 healthy subjects were examined.

Results: nTMS revealed a reduced cortical excitability in the patient group. Although the resting motor threshold was comparable in both groups (left/right hemisphere patients mean ± SD: 38,6 % ± 11,7 / 36,6 % ± 13,4 compared to subjects: 32,3 % ± 3,9 / 34,6 % ± 3,6, p=0,366) the corticospinal excitability estimated by the recruitment curve was reduced in the patient group (31,5 ± 38 / 48,7 ± 35,8 compared to healthy 149,5 ± 82,6 / 57,9 ± 35,8, p=0,007). Furthermore patients with severe impairment showed a higher cortical inhibition (208,4 ms ± 49 / 173,7 ms ± 39,2 compared to 139 ms ± 50,2 /148,1 ms ± 35,3, p=0,010) and reduced cortical representation (211,3 mm² ± 89,2 /217,9 mm² ±: 235,5 comparing with healthy: 455,3 mm² ± 251,4/ 402,9 mm² ± 143,5, p=0,009) revealing a functional restriction on the cortical level. These differences diminished in the postoperative follow-up control.

Conclusions: nTMS allows for detection of impairment of motor excitability in patients suffering from cervical myelopathy and demonstrates recovery of excitability after surgical decompression. nTMS might serve as a valuable prognostic factor in these patients in the future.