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 (ULabnormal group) were included for further analysis. Cases where CMCT was abnormal at the lower limbs only (LLabnormal) 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 ULabnormal, all patients had T2 hyperintensities, compared to none in LLabnormal (P=0.004). The C6-7 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 ULabnormal. The modified Japanese Orthopaedic Association scale tended to be lower in ULabnormal (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.