Miller Fisher syndrome (MFS), a variant of the Guillain-Barré syndrome (GBS), is 
characterized by ophthalmoplegia, ataxia, and areflexia. The annual incidence is 
around one patient per one million population. The antiganglioside anti-GQ1b IgG 
antibody has a role in the pathogenesis of the syndrome, especially of 
ophthalmoplegia. The presence of this antibody in the serum can be identified in 
over 80% of the patients, peaking in the first week, whereas albuminocytological 
dissociation in the cerebrospinal fluid (CSF) appears later. The most consistent 
electrophysiological findings in MFS are reduced sensory nerve action potentials 
and absent H reflexes. More variability is seen with F waves and various 
investigations involving cranial structures. Although there are usually no 
abnormalities in MFS by routine neuroimaging, in a few cases, contrast 
enhancement of nerve roots and signs of central nervous system involvement were 
described supporting the hypothesis of an anti-GQ1b-syndrome, a continuum 
involving GBS, MFS, and Bickerstaff's brainstem encephalitis. Owing to the lack 
of randomized trials, treatments used for GBS (intravenous immunoglobulin and 
plasmapheresis) are usually applied, although from retrospective analyses, the 
outcome was similar between treated and untreated subjects. The outcome of MFS 
is usually good with case fatality of < 5%. In the few autopsy cases, 
macroscopic abnormalities were generally not seen in the nervous system. 
Microscopic examination of the peripheral nervous system (including cranial 
nerves) showed segmental demyelination with minimal perivascular infiltration 
with normal spinal cord and brain stem.