[Value of magnetic stimulation and F-wave determination in diagnosis of proximal demyelinating lesions. Follow-up of acute Guillain-Barré polyradiculitis].

A 47-year-old woman developed acute Guillain-Barré-syndrome (GBS) within one day, presenting tetraparesis (muscle strength 1/5 for the upper and 2/5 for the lower extremities) and respiratory failure. On day 5 a cardiac pacemaker was necessary due to severe bradycardia. Electrophysiological studies were performed on days 2, 3, 5, 6, 8, 12, 15, 30 and 40. Our initial findings revealed normal motor conduction velocities and normal spinal motor evoked potentials. However, neither F-waves nor cortical motor evoked potentials could be registered from the upper or lower extremities. The motor conduction of the median nerve remained normal until day 6. The compound motor action potential declined thereafter and disappeared by day 12, indicating axonal degeneration. No axonal degeneration occurred in the lower extremities. The cervical or lumbar magnetic stimulation excites nerve roots at the level of the foramen intervertebrale. Thus, our findings suggest a conduction block between the foramen intervertebrale and the point where the nerve roots enter the spinal cord.