[Role of motor evoked potentials in the diagnosis of myelopathy associated with cervical spondylosis].

INTRODUCTION: Motor evoked potential (MEP) is the only method that is able to assess the function of the corticospinal tract in various neurological conditions, such as myelopathies. Myelopathy associated with cervical spondylosis, especially at an early stage, has often slight and non-specific clinical signs, pointing to the importance of the electrophysiological assessment of the spinal cord. The authors' aim was to investigate the sensitivity of MEP examination in the detection of myelopathy secondary to cervical spondylosis. PATIENTS AND METHODS: Patients were classified into three groups according to clinical signs and symptoms: Group I includes patients who have cervical spondylosis as demonstrated by MRI (narrowing of the spinal canal, discal herniation, spinal cord compression) but no complaints or signs suggestive of myelopathy. RESULTS: In Group II patients had minor, non-specific complaints, such as paraesthesia of the legs and gait disturbance raising the possibility of myelopathy, but neurological examination revealed no pyramidal signs. In Group III patients had pyramidal signs as well. In Group I corticospinal function was normal in all patients, as assessed by MEP examination. In Group II all patients had prolonged central motor conduction time or absent responses to cortical stimulation. Likewise, in Group III MEP revealed abnormal corticospinal function in all patients but one. CONCLUSIONS: In summary, MEP proved sensitive in the detection of corticospinal dysfunction in myelopathy associated with cervical spondylosis at a stage when clinical signs of pyramidal lesion are not yet present and patients have only minor complaints. On the other hand, if patients are completely symptom free with regard to myelopathy, MEP is also unlikely to disclose corticospinal dysfunction. If pyramidal lesion is evident already by clinical examination, MEP provides no further help. 'False-negative' results are also possible.