Guillain-Barré syndrome: a model of random conduction block.

In the Guillain-Barré syndrome clinical deficit is caused by failure of conduction in nerve fibres. Immunological mechanisms are generally held responsible, but the mechanism has not yet been elucidated. A recent longitudinal analysis of the distribution of lesions along the nerve trunks suggested two main patterns. In one of them, motor conduction block dispersed over the length of the nerve trunk was found, whereas sensory fibres were usually spared. For further pathogenetic studies of this subgroup, it is important to know whether conduction block occurs randomly or at preferred sites. As a tool to establish this, a model for conduction block is presented, based on a random distribution of lesions in the peripheral nerves. It is applicable to compound muscle action potentials (CMAP) obtained in routine EMG studies. Comparison of predicted and measured CMAPs in a first group of seven Guillain-Barré patients with evidence of conduction block supports the concept of a random distribution of lesions in this subgroup.