Anti-GQ1b antibody syndrome (AGABS) unifies triad-defined Miller Fisher syndrome (MFS), Bickerstaff brainstem encephalitis (BBE), and the ophthalmoplegic variant of Guillain-Barré syndrome (GBS-O) under a post-infectious immune mechanism centered on IgG to disialosyl gangliosides. The spectrum also encompasses triad-minus phenotypes-acute ophthalmoparesis without ataxia, acute vestibular syndrome, optic involvement, and acute sensory-ataxic neuropathy. A molecular-mimicry model with complement-mediated nodal/paranodal dysfunction explains severe early deficits despite bland limb nerve conduction studies (NCSs), the cranial/proprioceptive predilection, and generally favorable treatment responsiveness to immunotherapy. In practice, a serology-first strategy, complemented by targeted electrophysiology-blink and H-reflex testing, and, where feasible, paired SEP-ABR showing a literature-supported dissociation (normal ABR with impaired median-nerve cortical SEPs), which, in our series, was documented in one illustrative BBE case-and by structured neuro-otologic examination, mitigates the "normal-NCS trap" and enables timely treatment. Intravenous immunoglobulin (IVIg) is first-line; plasma exchange (PLEX) is an alternative in severe or IVIg-ineligible cases; and intravenous methylprednisolone (IVMP) may be added selectively for central/optic-weighted phenotypes without routine oral taper. We consolidate actionable diagnostic and therapeutic steps and examine them in an institutional series of 16 consecutive seropositive patients (2015-2025): all were anti-GQ1b-positive with frequent GT1a co-reactivity; most reported an antecedent infection-typically upper respiratory, less often gastrointestinal-within the two weeks before onset; limb NCSs were often nondiagnostic whereas reflex/evoked-potential studies were informative; two required intubation in addition to IVIg; outcomes were generally favorable with early immunotherapy. The practical message: order anti-GQ1b at first contact, pair targeted electrophysiology with neuro-otology, and treat early to exploit reversible nodal/paranodal dysfunction.

The discovery of the anti-GQ1b antibody has expanded the nosology of classic Miller Fisher syndrome to include Bickerstaff brainstem encephalitis, Guillain-Barré syndrome with ophthalmoplegia, and acute ophthalmoplegia without ataxia, which have been brought under the umbrella term anti-GQ1b antibody syndrome. It seems timely to define the phenotypes of anti-GQ1b antibody syndrome for the proper diagnosis of this syndrome with diverse clinical presentations. This review summarizes these syndromes and introduces recently identified subtypes. Although ophthalmoplegia is a hallmark of anti-GQ1b antibody syndrome, recent studies have identified this antibody in patients with acute vestibular syndrome, optic neuropathy with disc swelling, and acute sensory ataxic neuropathy of atypical presentation. Ophthalmoplegia associated with anti-GQ1b antibody positivity is complete in more than half of the patients but may be monocular or comitant. The prognosis is mostly favorable; however, approximately 14% of patients experience relapse. Anti-GQ1b antibody syndrome may present diverse neurological manifestations, including ophthalmoplegia, ataxia, areflexia, central or peripheral vestibulopathy, and optic neuropathy. Understanding the wide clinical spectrum may aid in the differentiation and management of immune-mediated neuropathies with multiple presentations.

We report a prospective study analysing clinical characteristics, subtyping and prognosis in Guillain-Barré syndrome (GBS). The study was based on consecutive GBS patients admitted between 2009 and 2017. Disability was serially assessed using the GBS disability scale. Fifty-six GBS patients were identified with an average age of 55 years (range, 5-86 years) and a male/female ratio of 2.1. The interval to nadir was <7 days in 59% of cases, and 7 to 28 days in the remainder; at nadir, 35.5% of patients were able to walk unaided, and 64.5% did not. Mechanical ventilation was needed in 20% of cases. There were two fatal cases. Clinical variants included paraparetic GBS seven cases, Miller Fisher syndrome one case, and acute sensory ataxic neuropathy (ASAN) one case. Serial electrophysiology showed a demyelinating pattern in 62.5% of cases, axonal in 28.5%, inexcitable in 1.8%, equivocal in 1.8%, and normal in 5.4%. Very early (1 to 4 days after onset) electrophysiology was done in 18 patients; equivocal or normal features in six of them evolved into an axonal pattern in four. Reversible conduction failure of sensitive nerves occurred in ASAN. Antiganglioside antibodies were only detected in axonal GBS. At 24-month follow-up, functional outcome did not differ between demyelinating and axonal GBS. Clinico-pathological correlation in an early fatal case is reported. This GBS study demonstrates comparable clinical features to previous investigations from well-defined populations. There was a relatively high prevalence of axonal GBS. We provide new pathophysiological insights on nerve conduction alterations.

Serum antibodies against glycolipids, mainly gangliosides, are detected in about 60% of patients with Guillain-Barré syndrome (GBS) and its variants. Anti-glycolipid antibodies play a crucial role in the pathogenic mechanisms of GBS. The antibody titer is the highest in the acute phase and decreases gradually. Molecular mimicries occur between the glycolipids and surface molecules on the infectious agents. Clinical subtypes of GBS are related to the antigenic specificities of the antibodies. The distribution of gangliosides in peripheral nervous tissues could explain the different clinical manifestations. The anti-GQ1b antibody is detected in 80-90% of patients with Fisher syndrome characterized by ophthalmoplegia. GQ1b is localized in the paranodes of the human cranial nerves innervating the extraocular muscles. This is consistent with the clinical association between the anti-GQ1b antibody and ophthalmoplegia. The anti-GM1 antibody is associated with acute motor axonal neuropathy, whereas the anti-GD1b antibody is detected in acute sensory ataxic neuropathy. GBS animal models sensitized by gangliosides, such as GM1 or GD1b, develop monophasic peripheral neuropathies. In the animal models, disruption of molecule clusters and deposition of complement products were observed in the nodal and paranodal regions. Clinical and experimental data suggest complement-mediated pathogenic mechanisms triggered by anti-glycolipid antibodies in GBS.