Controversy exists concerning whether Miller Fisher syndrome (MFS) is the result 
of a predominantly axonal or demyelinating polyneuropathy and whether the 
Guillain-Barré syndrome variant of acute ataxia and areflexia without 
ophthalmoplegia, ataxic Guillain-Barré syndrome (atxGBS), has a distinct 
pathophysiology. We explored these issues by reviewing the electrophysiologic 
features of 6 patients with MFS and 2 patients with atxGBS. EMG laboratory 
records were reviewed and electrophysiologic findings were categorized as axonal 
or demyelinating neuropathy using previously defined criteria. Of the 6 patients 
with MFS, 5 had electrophysiologic evidence suggestive of an axonal, 
predominantly sensory polyneuropathy; only 1 patient met criteria for 
demyelinating polyneuropathy. Both patients with atxGBS had demyelinating 
sensorimotor polyneuropathy. Electrophysiologic abnormalities in MFS typically 
suggest a predominantly axonal, sensory polyneuropathy, though demyelinating 
forms occur and may be under-diagnosed using current criteria. AtxGBS, in our 
experience, is a predominantly demyelinating polyneuropathy.