The definition of BBE has evolved since the original description, partly as a result of a classification of similar and, at times, overlapping disease entities such as the Miller Fisher syndrome (MFS) (see Lo3 for a review), Guillain-Barré syndrome (GBS) (see Griffin and Sheikh4 for a review), and acute demyelinating encephalomyelitis (ADEM) (see Tenembaum et al5 for a review), and partly because of the availability of new diagnostic tools, including MRI and anti-GQ1b antibody testing. There are a number of features shared by BBE and MFS, a variant of GBS, including a prodromal infection, ophthalmoplegia, decreased reflexes, and albuminocytological dissociation in the cerebrospinal fluid; the close relationship between BBE and MFS is supported by the presence in some patients with BBE of anti-GQ1b antibody, a frequent feature of MFS.2,6 However, in contrast to BBE, most cases of MFS show few if any signs of central nervous system involvement. Therefore, patients are generally classified as having BBE rather than MFS if there is evidence of corticospinal tract abnormalities, a disturbed state of consciousness, or a significant brainstem lesion on MRI or at autopsy. At times, there is an overlap between BBE and GBS, which prompted Odaka et al2 to classify some patients with BBE who had symmetrical flaccid limb weakness as having BBE associated with GBS; electrophysiological study results of these patients can suggest a motor axonal neuropathy, presumably representing an acute motor axonal neuropathy variant of GBS.7 One could also envision BBE as a brainstem-localized variant of ADEM, an immune-mediated inflammatory disease that usually affects the white matter of the brain and spinal cord and is often preceded by an infection. The similarities in BBE, MFS, GBS, and ADEM suggest their classification in a spectrum of autoimmune disorders that sometimes overlap.2 A number of different viral and bacterial infections have been implicated in the prodromal illness, including Campylobacter jejuni,8,9 raising the possibility that BBE can result from an autoimmune response to a number of different pathogens.