Preoperative diagnosis of the responsible level in CCM using CMAPs: comparison with SCEPs

Resting-state functional magnetic resonance imaging indices are related to electrophysiological dysfunction in degenerative cervical myelopathy

The age-related degenerative pathologies of the cervical spinal column that comprise degenerative cervical myelopathy (DCM) cause myelopathy due spinal cord compression. Functional neurological assessment of DCM can potentially reveal the severity and pathological mechanism of DCM. However, functional assessment by conventional MRI remains difficult. This study used resting-state functional MRI (rs-fMRI) to investigate the relationship between functional connectivity (FC) strength and neurophysiological indices and examined the feasibility of functional assessment by FC for DCM. Preoperatively, 34 patients with DCM underwent rs-fMRI scans. Preoperative central motor conduction time (CMCT) reflecting motor functional disability and intraoperative somatosensory evoked potentials (SEP) reflecting sensory functional disability were recorded as electrophysiological indices of severity of the cervical spinal cord impairment. We performed seed-to-voxel FC analysis and correlation analyses between FC strength and the two electrophysiological indices. We found that FC strength between the primary motor cortex and the precuneus correlated significantly positively with CMCT, and that between the lateral part of the sensorimotor cortex and the lateral occipital cortex also showed a significantly positive correlation with SEP amplitudes. These results suggest that we can evaluate neurological and electrophysiological severity in patients with DCM by analyzing FC strengths between certain brain regions.

Preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy. A retrospective study

STUDY DESIGN

Observational cohort study OBJECTIVES: To investigate preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy (CSA) using electrophysiological and neurological findings.

SETTING

Yamaguchi University METHODS: 54 patients with proximal CSA who underwent surgical treatment of the cervical spine were enrolled. Erb-point stimulated compound muscle action potentials (CMAP) were recorded from the deltoid and biceps brachii muscles. We computed the ratio of affected to normal side CMAP amplitudes in two muscles (deltoid and biceps brachii) and regarded the mean ratio (CMAP-R) as representing the severity of neural involvement. Pre- and postoperative strengths of the most atrophic muscles were evaluated using manual muscle testing. Improvements in strength were classified as excellent (5 grades recovered), good (more than one grade recovered), fair (no improvement), or poor (worsened).

RESULTS

Surgical outcomes were excellent in 26 patients, good in five, fair in 16, poor in seven. Patients with fair outcomes had lower CMAP-R than those patients with excellent and good outcomes [P = 0.0099, odds ratio = 0.89 (95% confidence interval, 0.81-0.97; for a change of 10%)]. Eight patients (15%) had a C5 palsy.

CONCLUSIONS

CMAP-R could be used as a reliable predictive factor related to a fair surgical outcome. We must pay attention to the incidence of C5 palsy after surgery.

A Novel Scoring System Associated With Surgical Outcome of Distal-type Cervical Spondylotic Amyotrophy

STUDY DESIGN

A single-center retrospective study.

OBJECTIVE

To elucidate the pathology of distal-type cervical spondylotic amyotrophy (CSA) and to assess predictive factors and a novel scoring system associated with surgical outcome.

SUMMARY AND BACKGROUND

Because of its rarity, the pathophysiology and surgical outcome of distal-type CSA are less well understood compared with proximal-type CSA.

METHOD

Surgical procedures were performed in 13 patients with distal-type CSA. Patients were classified into 2 groups: those with good recovery of muscle power (group 1, n=4) and those with fair recovery (group 2, n=9). All patients underwent magnetic resonance imaging. Central motor conduction time was recorded in abductor digit minim and compound muscle action potentials (CMAPs) were recorded in extensor carpi dig. Predictive factors associated with surgical outcome and a scoring system based on clinical, radiologic, and electrophysiological findings were evaluated. Twelve of 13 patients were scored for the following features: (1) duration of symptoms ≥13 months, (2) initial manual muscle testing ≤1, (3) multiple compressions in magnetic resonance imaging, (4) CMAPs amplitudes on affected side <1 mV, (5) CMAPs amplitudes on normal side <7.2 mV, (6) central motor conduction time longer than 7.4 ms, (7) the ratio of CMAPs amplitudes comparison with the normal side <50%.

RESULT

At final follow-up, 2 patients were graded excellent, 2 good, 9 fair, and 0 poor. None of the predictive factors was significantly different between groups 1 and 2. The mean score in group 2 (5.12±1.12) was significantly higher than for group 1 (2±1.15; P=0.006). Although all 8 patients in group 2 scored ≥4 points, all 4 patients in group 1 scored ≤3.

CONCLUSIONS

Comprehensive assessment using a scoring system is useful for predicting the surgical outcome of distal-type CSA. Surgeons should be aware that a score of ≥4 points correlates with poor surgical outcome on motor function.

Transcranial magnetic stimulation in the diagnosis of cervical compressive myelopathy: comparison with spinal cord evoked potentials

STUDY DESIGN

Single-center retrospective study.

OBJECTIVE

To reveal the characteristic changes in central motor conduction time (CMCT) produced by transcranial magnetic stimulation among the responsible levels of cervical compressive myelopathy (CCM).

SUMMARY OF BACKGROUND DATA

CMCT is a useful and noninvasive measure for evaluating the central motor pathway. However, a systematic correlation between CMCT findings and the responsible level of CCM has so far not been addressed in a large patient cohort.

METHOD

We measured CMCT in 75 patients with CCM who were determined by intraoperative spinal cord evoked potentials to have a single site of conduction abnormality at the intervertebral level. Twenty-one healthy controls were also evaluated. Motor evoked potentials, compound muscle action potentials, and F wave were recorded from bilateral abductor digiti minimi (ADM) and abductor hallucis (AH) muscles. CMCT was calculated as follows: motor evoked potentials latency-(CMAPs latency+F latency-1)/2 (ms).

RESULT

The mean values of ADM-CMCT and AH-CMCT at each responsible level were significantly longer than those of normal values (P<0.01). However, the mean value of ADM-CMCT at the C6-C7 level was markedly shorter than those at the other levels, whereas the mean values of AH-CMCT were not significantly different between each responsible level. We determined that an ADM-CMCT longer than 7.9 ms (mean+2.5 standard deviation) was abnormal. Using this definition, the sensitivity of ADM-CMCT for CCM was 92% for C3-C4 myelopathy, 95% for C4-C5, 58% for C5-C6, and 9% for C6-C7.

CONCLUSION

ADM-CMCT is useful for the screening of CCM rostral to the C5-C6 level. Diagnosis of patients with C6-C7 myelopathy should include assessment of the AH-CMCT.

LEVEL OF EVIDENCE

4.