Abnormal central motor conduction at the upper but not lower limbs correlates with severe cervical spondylosis: discussion of an unexpected observation

Abstract

Introduction: A novel pattern of transcranial magnetic stimulation (TMS) abnormalities in cervical spondylotic myelopathy (CSM) comprising abnormal central motor conduction time (CMCT) to the upper limbs and normal CMCT to the lower limbs was observed. CSM was more severe radiologically and tended to be more severe clinically when this pattern was encountered.

Case presentation: To further characterize this observation, 414 consecutive TMS evaluations of cervical spondylosis were reviewed. Those cases in which (a) CMCT was abnormal at the upper and (b) normal at the lower limbs and (c) a cervical spine magnetic resonance imaging (MRI) was available (UL_abnormal group) were included for further analysis. Cases where CMCT was abnormal at the lower limbs only (LL_abnormal) were used for comparison. MRI-measured sagittal and parasagittal diameters of the spinal canal at all intervertebral levels and cervical spinal cord T₂ hyperintensities were compared between these groups. Four patients fulfilled all inclusion criteria in each group. In UL_abnormal, all patients had T₂ hyperintensities, compared to none in LL_abnormal (P=0.004). The C_6-7 right (6 mm±1.05 vs 8.48 mm±4.01, P=0.05) and left (6.58 mm±1.39 vs 9.17 mm±5.03, P=0.06) parasagittal spinal canal diameters tended to be smaller in UL_abnormal. The modified Japanese Orthopaedic Association scale tended to be lower in UL_abnormal (11.5±2.65 vs 15.75±0.96, P=0.13).

Discussion: CMCT abnormalities isolated to the upper limbs constitute a less frequent pattern of involvement, which may correlate with more severe CSM.

Keywords: Evoked potentials; Spinal cord diseases.

Figure 1

An axial T₂ MRI section of UL_abnormal patient #4 at the C_5–6 level and the related spinal canal dimensions.

Figure 2

Comparison of mean spinal canal diameters and T₂ hyperintensities at all intervertebral levels for the UL_abnormal and LL_abnormal groups. At C_5–6 and C_6–7 mean diameters in UL_abnormal are smaller, especially UL_abnormal d_{mri_right} and d_{mri_left}, for which the differences are borderline significant. T₂ hyperintensities are significantly more frequent in UL_abnormal.