Electrophysiological correlates of pyramidal signs and clinical motor status: a “real world” TMS study

Introduction: few non-recent evidences on the transcranial magnetic stimulation (TMS) correlates of pyramidal signs and clinical motor status were reported. We assessed motor evoked potentials (MEPs) in patients with pyramidal signs and motor deficit compared to those with pyramidal signs without clinical weakness. Methods: 43 patients with cervical spondylotic myelopathy were dichotomized in 21 with pyramidal signs and mild motor deficit (Group 1) and 22 with pyramidal signs and normal strength (Group 2), both compared with 33 healthy controls (Group 0). MEPs were recorded through a circular coil on the “hot spot” of the First Dorsal Interosseous and Tibialis Anterior (TA) muscle, bilaterally. Central motor conduction time (CMCT) was estimated as the difference between MEP cortical latency and peripheral motor latency by magnetic stimulation. Peak-to-peak MEP amplitude and right-to-left differences were also measured. Results: the three groups were matched for age, sex, and height. MEP latency at four limbs and CMCT at lower limbs were significantly prolonged in Group 1 with respect to the other two. Compared to the same groups, MEP amplitude from TA bilaterally was significantly decreased in Group 1 (Table 1 and 2). Unlike motor deficit, pyramidal signs were not significantly and independently associated with any TMS measure, also when age, sex, and height were considered as confounding factors (Table 3). Conclusion: in a “real world” clinical environment, routine MEPs represent an accurate diagnostic test in cervical spondylotic myelopathy patients with even mild motor deficit, whereas clinically isolated pyramidal signs may not be associated, at this stage, with gross TMS changes.