Somatosensory evoked potentials and nerve conduction studies in patients with Guillain-Barré syndrome.

Somatosensory evoked potentials, F-waves, and nerve conduction studies (NCS) were performed to determine their usefulness in detecting electrophysiologic abnormalities in 23 children in the acute stage of Guillain-Barré syndrome. The studies were performed on average 8.3 days after the onset of neurological symptoms, before the period of maximal weakness. All patients had at least one abnormal test. Somatosensory evoked potentials (SEP) showed most abnormalities: 91% abnormal recordings with posterior tibial nerve (PTN) stimulation and 68% with median nerve (MN) stimulation. The nerve conduction velocities were abnormal in 76% and 67% with PTN and MN stimulation, respectively. The F-waves were abnormal in 66% (PTN) and 56% (MN). The SEP studies were helpful in detecting proximal and central conduction abnormalities in 26% of patients, and they were more sensitive in detecting an abnormality when compared with F-wave recordings. Furthermore, in one patient with normal NCS and F-waves the prolonged lumbar potential-P35 conduction time of the PTN-SEP was the only abnormality found. SEP can detect an abnormality and thus support the clinical diagnosis of Guillain-Barré syndrome in the acute stage when the results of more conventional tests are inconclusive.