gms | German Medical Science

Objective: In patients suffering from degenerative cervical myelopathy (DCM), conventional radiology with additional electrophysiology often fails to reliable quantify stage of disease and dynamics of disease progression. We have recently introduced the concept of ‘corticospinal reserve’ in which severely symptomatic patients (JOA<12) with an exhausted reserve presented with a restricted motor area, reduced recruitment curve and increased inhibition. In contrast, patients suffering from mild symptoms (JOA>12) and thus preserved corticospinal reserve, an enlarged motor area due to a higher recruitment of adjacent neuronal groups was observed. The current prospective multicenter trial has been designed to validate this new pathophysiological concept and demonstrate its diagnostic potential in DCM.

Methods: We investigated 120 patients (mean age 64.5 ± 11.8 yrs.) with DCM preoperatively and following surgical decompression from four spine centers in Germany and Switzerland. The study was sponsored by a DWG research grant. Patients were divided into three groups, based on the initial Japanese Orthopedic Association Score (JOA <12/13-15/>15). In addition, conventional electrophysiology (SSEP/MEP) and the “Disabilities of Arm, Shoulder and Hand Questionnaire” (DASH) were recorded. For the assessment of corticospinal excitability, we measured the resting motor threshold (RMT), motor area, recruitment curve (RC) and cortical silent period (CSP) by means of navigated transcranial magnetic stimulation (nTMS).

Results: In patients with moderate symptoms (JOA 13-15) we encountered a compensatory increased motor cortex activation (motor area: p<.05: mean ± SD JOA 13-15: 308.5 ± 213.3 vs. JOA ≤12: 225.7 ± 159.5) and maintained corticospinal excitability (RC slope p=0.4, JOA 13-15: 10.6 ± 6 vs. JOA >15: 11.1 ± 5.2). In contrast patients with severe symptoms (JOA≤12) presented a reduced excitability of cortico-cortical axons reflected by an elevated RMT (p<.05, mean ± SD JOA ≤12: 43.8 ± 11.4 vs. JOA >15: 39.2 ± 8.4) and reduced corticospinal excitability expressed by a lower RC slope (p<.05, mean ± SD JOA ≤12: 8.4± 4.8 vs. JOA >15: 11.1± 5.2). The conventional electrophysiology revealed only 73.3% pathological SSEPs for patients with a severe impairment (JOA <12), 65.8% for moderate symptoms (JOA 13-15) and 27,3% for mild symptoms (JOA >15).

Conclusion: In summary, our prospective multicenter trial has confirmed our concept for functional reorganization in patients suffering from DCM i.e. the ‘corticospinal reserve capacity’. Based on our findings it became apparent that conventional diagnostics often fail to demonstrate clinical impairment and disease progression. The corticospinal reserve might be able to overcome the diagnostic gap in DCM and serve as an objective and valuable tool for future treatment strategies in these patients.