[Central motor conduction time in diagnosis of spinal processes]

In patients with extra- and intramedullary spinal disorders (32 cases with myelopathy due to cervical spondylosis, 11 with syringomyelia and 17 with spinal tumours) central motor conduction time (CMCT) was studied after transcranial magnetic stimulation of the cortex. Compound muscle action potentials (CMAP) were recorded from abductor digiti minimi muscle (ADM) and anterior tibial muscle (TA) bilaterally. Of 37 patients with extramedullary located cervical lesions CMCT to the ADM was abnormal in 51% (n = 19) and to the TA in 70% (n = 26). In 10 patients with intramedullary cervical lesions abnormal CMCT to the ADM as well as to the TA was observed in 30% (n = 3) each. In extramedullary disorders measurement of CMCT to the TA was more sensitive in detecting impaired central motor conduction, though not significantly. Prolonged CMCT correlated to clinical signs of upper motor neuron involvement and to spinal cord compression. In addition, the method proved useful for detection of subclinical lesions of corticospinal pathways. The different results between intra- and extramedullary affections are explained by the anatomical localisation of pyramidal tract fibers.