The Corticospinal Reserve Capacity: Reorganization of Motor Area and Excitability As a Novel Pathophysiological Concept in Cervical Myelopathy.

BACKGROUND

In degenerative cervical myelopathy (DCM), the dynamics of disease progression and the outcome after surgical decompression vary interindividually and do not necessarily correlate with radiological findings.

OBJECTIVE

To improve diagnostic power in DCM by better characterization of the underlying pathophysiology using navigated transcranial magnetic stimulation (nTMS).

METHODS

Eighteen patients with DCM due to cervical spinal canal stenosis were examined preoperatively with nTMS. On the basis of the initial Japanese Orthopedic Association (JOA) Score, 2 patient groups were established (JOA ≤12/>12). We determined the resting motor threshold, recruitment curve, cortical silent period, and motor area. Accordingly, 8 healthy subjects were examined.

RESULTS

Although the resting motor threshold was comparable in both groups (P = .578), the corticospinal excitability estimated by the recruitment curve was reduced in patients (P = .022). In patients with only mild symptoms (JOA > 12), a compensatory higher activation of non-primary motor areas was detected (P < .005). In contrast, patients with severe impairment (JOA ≤ 12) showed a higher cortical inhibition (P < .05) and reduced cortical motor area (P < .05) revealing a functional restriction on the cortical level.

CONCLUSION

Based on these results, we propose a new concept for functional compensation for DCM on the cortical and spinal level, ie corticospinal reserve capacity. nTMS is a useful tool to noninvasively characterize the pattern of functional impairment and compensatory reorganization in patients suffering from DCM. The change in nTMS parameters might serve as a valuable prognostic factor in these patients in the future.