Axonal conduction block at intermediate nerve segments in pure motor Guillain-Barré syndrome

The pathophysiology of axonal Guillain-Barré syndrome (GBS) is not simple axonal degeneration, but includes reversible conduction failure. Acute motor axonal neuropathy (AMAN) and acute motor conduction block (CB) neuropathy are the two subtypes of pure motor axonal GBS, but their nosologic boundary is still in debate. We investigated clinical and electrophysiological features of 21 consecutive patients with GBS in Korea. Analysis was focused on the presence of CB at intermediate nerve segments (iCB) in pure motor GBS, and its serial changes during the acute phase of disease. Pure motor GBS was common (81%), and iCB was observed in 12 patients with pure motor GBS. Clinical features of pure motor GBS with iCB were distinct from sensorimotor GBS, but similar to pure motor GBS without iCB, characterized by frequent preceding diarrhea, uncommon cranial nerve palsy, and fast recovery. The iCB was not restricted to common entrapment sites, and the distal segments were also commonly involved in the nerves with iCB. The temporal course of iCB was marked by a rapid and often disproportionate increase of proximal and distal amplitudes without remyelinating slow components. Clinical and electrophysiological features of pure motor GBS in patients with iCB suggest that acute motor CB neuropathy may constitute a spectrum of axonal GBS, sharing a common pathomechanism with AMAN.