Fisher syndrome with tetraparesis and antibody to GQ1b: Evidence for motornerve terminal block

A Fisher syndrome (FS) patient with antibody to tetrasyaloganglioside GQ1b (GQ1b) developed late limb weakness. Serial motor conduction velocities (MC Vs) showed a marked reduction of distal compound muscle action potential (C MAP) amplitudes, worse at 2-3 weeks, followed by a dramatic increase in wee k 5, Motor conduction velocities were always in the normal range, distal mo tor latencies changed only slightly, and conduction block in intermediate n erve segments was absent. These electrophysiological data might suggest an axonal neuropathy or a distal demyelinating conduction block. However, the dramatic increase of distal CMAP amplitudes over a short time without signi ficant changes of distal motor latencies, CMAP duration, and morphology ind icate that weakness in this FS patient might be due to a block of acetylcho line release from motor terminals, possibly mediated by anti-GQ1b antibodie s. (C) 1999 John Wiley & Sons, Inc.