Trans-synaptic degeneration of motoneurons distal to chronic cervical spinal cord compression in cervical spondylotic myelopathy.

OBJECTIVE

To assess the effect of chronic cervical spinal cord compression upon remote motor unit function in patients with cervical spondylotic myelopathy (CSM).

METHODS

Fifty-three CSM patients and 47 healthy subjects were included. Bilateral motor unit number estimations (MUNEs) were recorded from both abductor digiti minimi and abductor pollicis brevis, and bilateral flexor carpi radialis (FCR) H-reflexes were examined in all subjects along with the nine-hole peg test (NHPT). The main outcome measures included the number of motor units, the average single motor unit potential (SMUP) area, the FCR Hmax/Mmax ratios and the NHPT time.

RESULTS

Statistically significant results compared to healthy controls included increased average SMUP area, increased FCR Hmax/Mmax ratio and increased NHPT time (p < 0.05). Abnormal SMUP was observed in 10/53 (18.9%) CSM patients along with reduced motor units in 3 of these 10 patients, while the FCR Hmax/Mmax ratios in the CSM patients with abnormal MUNE were higher than those in others (p < 0.05). There was a positive correlation between the NHPT time and the average SMUP area, and a negative correlation was noted between the NHPT time and the number of motor units (p < 0.05).

CONCLUSION

In CSM patients, the motor units below the level of compression may exhibit dysfunction, which is likely a result of trans-synaptic degeneration. Both cervical spinal cord compressive injury and this trans-synaptic degeneration contribute to the impairment of fine motor ability in CSM patients. Therefore, treatment and rehabilitation efforts should account for these two dysfunctions.