Question: Which antibody is implicated in the Bickerstaff's brainstem encephalitis?

Context:
In addition, BBE and Fisher syndrome, which are clinically similar and are both associated with the presence of the immunoglobulin G anti-GQ1b antibody, represent a specific autoimmune disease with a wide spectrum of symptoms that include ophthalmoplegia and ataxia.
The syndrome defined by Bickerstaff of progressive, external ophthalmoplegia and ataxia, with disturbance of consciousness or hyperreflexia, has subsequently been associated with anti-GQ1b antibodies.
An anti-GQ1b antibody syndrome has been proposed to underlie the common pathophysiology for the three disorders; however, other studies have found a positive anti-GM1 instead of anti-GQ1b antibody.
Serologic analysis of antibodies against ganglioside complexes (anti-GDIa, anti-GDIb, anti-GM1, anti-GM2, anti-GM3, anti-GQIb and anti-GTIb antibodies) showed negative results.
However, contrary to a proposed anti-GQ1b antibody syndrome, we would suggest that pathogenesis of this clinical spectrum is not limited to anti-ganglioside antibodies.
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. 
Anti-GM1 IgG, GD1a IgG, GQ1b IgG, and GT1a IgG antibodies were positive.
The discovery of the association of the anti-GQ1b IgG antibody with the postinfectious clinical syndromes of ophthalmoplegia, ataxia, and areflexia helped house the phenotypes of the Miller Fisher syndrome (MFS), atypical MFS, Guillain-Barré syndrome with ophthalmoplegia, and Bickerstaff's brainstem encephalitis under one roof. 
These findings suggest that host susceptibility may play a role in inducing the production of anti-ganglioside antibodies and the development of Bickerstaff's brainstem encephalitis.
These antibodies should provide useful serological markers for identifying patients who have atypical GBS with preserved deep tendon reflexes, ataxic GBS, Bickerstaff's brainstem encephalitis or acute ophthalmoparesis, especially for those who have no antibodies to GM1, GD1a or GQ1b.
Bickerstaff brainstem encephalitis and Fisher syndrome: anti-GQ1b antibody syndrome.
Among them, only one patient developed Bickerstaff's brainstem encephalitis, who carried anti-GQ1b IgG antibodies.
Overlapping Guillain-Barré syndrome and Bickerstaff's brainstem encephalitis associated with anti-GQ1b IgG antibody after herpes simplex virus infection.
Bickerstaff's brainstem encephalitis, Miller Fisher syndrome and Guillain-Barré syndrome overlap in an asthma patient with negative anti-ganglioside antibodies.
Bickerstaff brainstem encephalitis is a clinical syndrome of ophthalmoplegia, cerebellar ataxia, and central nervous system signs and is associated with the presence of anti-GQ1b antibodies.
This is only the second case in the literature of Bickerstaff brainstem encephalitis with raised titers of anti-GQ1b antibodies described in association with M pneumoniae infection.
Of those patients with Fisher syndrome, Bickerstaff's brainstem encephalitis, ataxic GBS or acute ophthalmoparesis, 33% of 67 anti-GM1b-positive, and 52% of 25 anti-GalNAc-GD1a-positive patients had no anti-GQ1b antibodies.
Fisher syndrome or Bickerstaff brainstem encephalitis? Anti-GQ1b IgG antibody syndrome involving both the peripheral and central nervous systems.
Anti-GQ1b antibody has been found in Miller Fisher syndrome (MFS), Guillain-Barré syndrome (GBS) with ophthalmoplegia, Bickerstaff brainstem encephalitis (BBE), and acute ophthalmoplegia without ataxia (AO).
This case presented clinical characteristics of three syndromes concurrently-Fisher syndrome, Bickerstaff brainstem encephalitis, and Guillain-Barré syndrome-that may be collectively called 'anti-GQ1b IgG antibody syndrome'.
This is the case of a 79-year-old man with chronic lymphocytic leukemia who presented with Guillain-Barré syndrome with features overlapping with the Miller Fisher syndrome and Bickerstaff brainstem encephalitis and positive antiganglioside GQ1b antibody about 6 months after treatment with bendamustine and rituximab.
Bickerstaff brainstem encephalitis and Fisher syndrome: anti-GQ1b antibody syndrome
[A case report of Bickerstaff's brainstem encephalitis with positive anti GQ 1 b, GT 1 a, GM 1 ganglioside antibodies].
[Probable Bickerstaff's brainstem encephalitis associated with anti-GQ1b antibody].
Among them, only one patient developed Bickerstaff's brainstem encephalitis, who carried anti-GQ1b IgG antibodies. 
Nevertheless, 66% of patients with Bickerstaff syndrome have anti-GQ1b antibody during the acute phase period.
Among them, only one patient developed Bickerstaff's brainstem encephalitis, who carried anti-GQ1b IgG antibodies.
Overlapping Guillain-Barré syndrome and Bickerstaff's brainstem encephalitis associated with anti-GQ1b IgG antibody after herpes simplex virus infection.

Answer: The syndrome defined by Bickerstaff of progressive, external ophthalmoplegia and ataxia, with disturbance of consciousness or hyperreflexia, has subsequently been associated with antiganglioside antibody, anti-GQ1b
Exact answer: antiganglioside antibody