Clinical manifestations

Presentation and course

Presentation is typically seasonal, with fall (84%) and spring (16%) predominance (63). Patients with "anti-GQ1b antibody syndrome" can present with a range of neurologic features. The classical triad of ophthalmoplegia, ataxia, and areflexia continues to be the commonest presentation in Miller Fisher syndrome (15; 26). Ophthalmoplegia seems to be the most prevalent and consistent finding in Miller Fisher syndrome and can be the result of central and/or peripheral localizations (69; 39). A central lesion is suggested by the presence of concomitant strabismus (ocular misalignment does not change according to the direction of gaze or which eye is fixating on the target), preservation of Bell phenomenon, and adduction palsy, which is overcome by convergence (39). Acute concomitant strabismus in 13% of 84 patients with anti-GQ1b antibody associated ophthalmoplegia has been described and manifests most commonly as esotropia (39). Patients with a central lesion accounting for their ophthalmoplegia more frequently have spontaneous, gaze evoked, positional nystagmus and saccadic hypermetria than those with paralytic (peripheral) strabismus and are less likely to show ptosis or iridoplegia (39). Internuclear ophthalmoplegia was also described in the anti-GQ1b syndrome (39). Patients with peripheral lesions develop a relatively symmetrical external ophthalmoplegia (76%), but the condition can also be unilateral. Abduction deficit was the most common finding (33%) (69). Similar findings can be seen in acute ophthalmoplegia without ataxia. Internal ophthalmoplegia is a frequent finding, particularly in patients exhibiting limb weakness and in Bickerstaff variants (52). Light-near dissociation has been reported.

Of note is that limb and gait “cerebellar-like ataxia” can also be the initial presenting symptoms and is accompanied in 75% of cases by distal limb loss of proprioception (49) and negative Romberg sign (85). Common sensory complaints include paresthesias matched by reduced pin (7%) and vibratory sense (17%) (26). Aside from these two characteristic features, other clinical features are recognized. In a study of 50 consecutive patients with Miller Fisher syndrome there were signs of blepharoptosis (58%) and pupillary mydriasis (42%), both occurring frequently at the height of illness (49) (see Clinical vignette case #1). Some patients were also noted to have facial (32%) and bulbar palsy (26%). Sensory symptoms are less frequent than would be expected given the gross ataxia. Although atypical, some patients with Miller Fisher syndrome may have a Babinski sign and rarely require ventilatory support (26). There have been additional reports on the development of delayed facial palsy in patients with Miller Fisher syndrome (29; 70; 71). In such instances, facial palsy develops after cardinal features of Miller Fisher syndrome have reached a nadir or started to improve.

The spectrum of "anti-GQ1b antibody syndrome” includes acute ophthalmoplegia, acute ptosis, acute mydriasis, acute oropharyngeal palsy, acute ataxic neuropathy (without ophthalmoplegia), and acute vestibular syndrome (40).

Bickerstaff brainstem encephalitis represents the other end of the spectrum of "anti-GQ1b antibody syndrome," where patients present not only with ataxia and ophthalmoplegia, but also features that suggest involvement of the CNS, such as altered levels of consciousness and brisk reflexes (05). Patients can also present with an overlap of the pharyngeal-cervical-brachial variant of Guillain-Barré syndrome (53; 50). Atypical presentations of Bickerstaff brainstem encephalitis with only hypersomnolence and ataxia, without ophthalmoplegia, have also been reported and have been associated with the presence of GQ1b antibodies supporting the diagnosis (75). The area postrema syndrome, characterized by intractable nausea, vomiting, or hiccups has also been described in a small group of patients with Bickerstaff brainstem encephalitis; however, no GQ1b antibodies were detected in such cases (86). A paper from the GBS Classification Group proposed inclusive diagnostic criteria that can facilitate early diagnosis of variants of Miller Fisher syndrome (76).

A retrospective study reported the differences in clinical characteristics between GQ1b antibody-positive and antibody-negative Bickerstaff brainstem encephalitis. Compared to patients without antibodies, those with antibodies had more frequent preceding upper respiratory infection (70% vs. 20%) and paresthesias (44% vs. 0%), less frequent brain MRI abnormalities (8% vs. 50%), lower median CSF cell count (12.5/µL vs. 75.9/µL) lower median protein levels (63.5 mg/dL vs. 159 mg/dL), and shorter median time to get recovery of consciousness (10 days vs. 23 days), indicating that Bickerstaff brainstem encephalitis with GQ1b antibodies has homogeneous features (80).

Prognosis and complications

The functional outcome of patients with anti-GQ1b antibody syndrome is usually good in either typical Miller Fisher syndrome or Bickerstaff brainstem encephalitis. In Miller Fisher syndrome, patients tend to make a spontaneous recovery. Improvement in ataxia is reported to start at a median of 12 days (range, 3 to 41 days) after the onset, followed closely by improvement in ophthalmoplegia, median 15 days (range, 3 to 46 days). The median periods between the onset and complete recovery of ataxia and ophthalmoplegia were 32 days (range, 8 to 271 days) and 88 days (range, 29 to 165 days), respectively (49). Facial palsy may develop subsequently, even when ataxia or ophthalmoplegia have started to improve (29; 70; 71).

Although Miller Fisher syndrome can recur following an antecedent illness, when associated with anti-GQ1b antibodies, the outcome is favorable in most patients (20). In a study, recurrences occurred more frequently in patients with Miller Fisher syndrome or Bickerstaff brainstem encephalitis compared with those with Guillain-Barré syndrome (25). Symptoms and signs were less severe during relapses than during the initial episode in recurrent patients (25) (see Clinical vignette case #2).

Bickerstaff brainstem encephalitis is also associated with a good recovery, but mortality has been described (05; 02; 53), which may be due to a central respiratory depression or secondary to complications such as a concurrent infection. The majority of patients will achieve complete remission by six months, but in a minority, symptoms of paresthesias, diplopia, or ataxia may persist (53).

Overlap can occur between Miller Fisher syndrome and Guillain-Barré syndrome as well as other variants including pharyngeal-cervical-brachial variant and Bickerstaff brainstem encephalitis. A study found the overlap syndrome to occur in 50% of pure Miller Fisher syndrome cases, typically within seven days of the onset of Miller Fisher syndrome (66). In cases where there is an overlap of Guillain-Barré syndrome the prognosis will depend on the severity of Guillain-Barré syndrome. Limb weakness can persist for those who have a severe axonal degeneration. Complications related to autonomic dysfunction such as cardiac arrhythmias should also be borne in mind, and close monitoring is warranted in the early stages of the illness. A case of Takotsubo cardiomyopathy associated with Bickerstaff brainstem encephalitis has also been reported (64).

Clinical vignette

Below are two cases. Case 1 is a picture of eye movements recorded from a 39-year-old woman who developed total ophthalmoplegia and facial diplegia associated with GQ1b antibodies (see case 1 figure); case 2 is a 39-year-old man who developed a total of four episodes of Guillain-Barré syndrome or Miller Fisher syndrome.

Case 1: Eye movements with facial diplegia.

Case 2: Representative case of recurrent Guillain-Barré syndrome or Miller Fisher syndrome.

A 39-year-old man was admitted to the hospital with Miller Fisher syndrome in 2004, but he had two similar episodes that required hospitalizations in 1994 and 1998.

In February 1994, at 29 years of age, the patient was admitted to another hospital with a diagnosis of Guillain-Barré syndrome.

The patient had been well until two weeks before admission, when fever, vomiting, and diarrhea developed, followed by diplopia, bilateral leg weakness, tingling sensation in his left arm and bilateral legs, and dysphagia. He was initially treated with oral prednisolone 15 mg daily at a local clinic, but muscle weakness further progressed in all limbs, ultimately leading to a hospitalization to a local hospital. The patient was initially treated with intravenous high-dose methylprednisolone but soon transferred to another hospital where he was diagnosed with Guillain-Barré syndrome and started on immunoadsorption plasmapheresis followed by double filtration plasmapheresis, resulting in improvement. He was discharged on the 22nd hospital day with mild bilateral abducens palsy, hyporeflexia, and mild muscle weakness but his symptoms had resolved subsequently.

Four years later, in December 1998 at 33 years of age, the patient was readmitted to the same hospital with a similar episode. Two weeks before admission, sore throat and cough developed. Then he began to have diplopia, dizziness, and tingling sensation in the left hand and sole of the feet. On admission the patient had bilateral abducens palsy, ataxia, areflexia, mild weakness, and mild bulbar palsy. GQ1b IgG antibodies were detected in the serum. The patient was treated with four rounds of immunoadsorption plasmapheresis, resulting in resolution of his symptoms. On discharge he had mild horizontal diplopia and hyporeflexia, but the diplopia subsequently disappeared.

Six years later, in May 2004 at 39 years of age, the patient was admitted to our hospital with recurrence of Miller Fisher syndrome. One week before admission, sore throat and cough developed without fever. One day before admission, diplopia and tingling sensation in his left hand and leg developed. He also had severe anorexia and nausea. The next day dizziness, dysesthesia in the right hand, and retroorbital pain also developed. He was admitted to our hospital.

On examination the temperature was 37.0°C, the blood pressure 112/70 mm Hg, and the pulse 72 beats per minute. Physical examination was unremarkable. On neurologic examination the patient was alert and well oriented. His speech was normal. The pupils were 4.0 mm, equal, both reacted sluggishly to light. Both eyes were esotropic in primary position; there was bilateral abduction palsy, mild upward gaze palsy, and ptosis on the right. There was no nystagmus. The remainder of the function of the cranial nerves was intact, including the muscle power of the orbicularis oculi. He had mild weakness in his neck flexor, bilateral biceps brachii and triceps brachii, and left hip flexor; the grip strength was 29 kg on the right and 13 kg on the left. He complained of dysesthesias in the tips of the fingers of the left hand, but sensory examination was normal, including vibration and position sense. The deep tendon reflexes were diminished except the left biceps and triceps jerks, which were normal; the plantar response was flexor bilaterally. Coordination was intact in the upper limbs but mildly impaired in the left lower limb on heel-shin test. He was not able to walk due to truncal ataxia and severe nausea. The neck was supple.

The blood test results were unremarkable except elevated level of serum CRP (1.12 mg/dL). CSF examination on the day of admission (day 1) revealed one white blood cell/µL, with normal protein level (25 mg/dL). A brain MRI did not show abnormal enhancement along the affected cranial nerves. A nerve conduction study and electroencephalogram were unremarkable.

The patient was initially suspected as Miller Fisher syndrome or Guillain-Barré syndrome with ophthalmoplegia and he was started on IVIg (0.4 g/kg/day, 5 days) on day 1. The symptoms, including muscle weakness, had progressed for seven days and the right eye became midline fixed; however, after reaching the peak, the symptoms started improving, without additional immunotherapy. The follow-up CSF examination obtained on day 8 revealed 10 white blood cells/µL with elevated protein levels (51 mg/dL). The serum was positive for GQ1b IgG antibodies (1:3200) but negative for other IgG antibodies against GM1, GD1b, GD1a, GT1b, GM2, and GalNAc-GD1a; GT1a antibodies were not examined at that time. He was discharged on day 25, with mild right abduction palsy, which resolved subsequently.

Nine years later, in early March 2013 at 48 years of age, the patient was readmitted to our hospital with recurrent similar episode. Twelve days before admission, cough, sore throat, and low-grade fever developed. One day before admission on awakening he noticed diplopia and dysesthesias in the tips of all fingers and toes and perioral area. He was admitted to our hospital.

On examination the temperature was 38.4°C, the blood pressure 114/77 mm Hg, and the pulse 86 beats per minute. Physical examination was otherwise unremarkable. The patient was alert and well oriented. His speech was normal. There was bilateral ptosis (more affected on the right than the left). The pupils were 4.0 mm, equal, and both did not react to light. The eye movements were mildly restricted in all directions bilaterally with monocular nystagmus on the left eye on looking to the left. Muscle power of the orbicularis oculi was weak on both sides. Muscle strength was normal in all limbs. Sensory examination was unremarkable except mild reduction of vibration sense in the legs and subjective tingling sensation in his perioral area and distal parts of all limbs. Coordination was intact on finger-nose tests and heel-shin tests, but he was not able to walk without assistance. Romberg sign was negative. The deep tendon reflexes were diminished in all limbs.

The blood test results were unremarkable. CSF examination on admission (day 1) revealed one white blood cell/µL, with normal protein level (27 mg/dL), without CSF-restricted oligoclonal band detection. A brain MRI was normal. A nerve conduction study was unremarkable but H-reflex study showed decreased H/M amplitude ratio.

After admission the patient was started on IVIg. Ophthalmoplegia and limb ataxia progressed for six days, resulting in total ophthalmoplegia (mid-line fixed on both eyes) but after day 8 dysesthesias and ataxia started improving, followed by gradual improvement in ophthalmoplegia. The patient became able to walk independently on day 13 and he was discharged on day 18. On discharge ophthalmoplegia still persisted but eye movements had almost recovered on the last visit 51 days after the onset of Miller Fisher syndrome; areflexia remained diminished.

In the fourth episode both GQ1b IgG antibodies (1:6400) and GT1a IgG antibodies (1:12,800) were detected but there were no IgG antibodies against GM1, GD1b, GD1a, GT1b, GM2, and GalNAc-GD1a (< 1:100).

In summary, the patient developed four similar episodes compatible with a diagnosis of Guillain-Barré syndrome with ophthalmoplegia at the first episode and Miller Fisher syndrome in the subsequent ones. Although it is rare, recurrent Guillain-Barré syndrome or Miller Fisher syndrome can occur. In this patient, GQ1b antibodies were detected in three of three examined episodes, and GT1a antibodies were also found at high titers, concurrent with GQ1b antibodies in the fourth episode (but not examined in the other episodes). It is unclear whether IVIg hastened recovery in the last two episodes of typical Miller Fisher syndrome, in which spontaneous recovery is the rule, but we used IVIg because the patient had developed bulbar palsy and muscle weakness in the first two episodes.

Biological basis

Etiology and pathogenesis

Some authors have argued a central etiology in Miller Fisher syndrome and Bickerstaff brainstem encephalitis (02), suggesting that ophthalmoplegia and ataxia were due to brainstem and cerebellar lesions respectively. However, some patients with Miller Fisher syndrome develop limb weakness and progress to Guillain-Barré syndrome during the clinical course of the illness (49). The existence of such overlapping cases, along with the presence of antecedent infection and CSF albuminocytological dissociation, strongly suggest that Miller Fisher syndrome is a variant of Guillain-Barré syndrome, and that the condition is an autoimmune disease triggered by microorganisms. In a study of 62 patients with Bickerstaff brainstem encephalitis diagnosed by the strict criteria of progressive, relatively symmetrical external ophthalmoplegia and ataxia by four weeks along, with a disturbance of consciousness or hyperreflexia, the authors described flaccid symmetrical tetraparesis in 60% of patients, suggesting an overlap of Guillain-Barré syndrome with some Bickerstaff brainstem encephalitis cases.

Following the identification of IgG autoantibodies against GQ1b in patients with Miller Fisher syndrome, the authors proposed these GQ1b antibodies as a diagnostic marker of Miller Fisher syndrome (09). Due to the differences in methods and cutoff values, serological results differ somewhat among representative laboratories; however, GQ1b antibodies occur in 83% (n=466) (26), 96% (n=24) (07), 85% (n=23) (74), and 100% (n=9) (77) of patients with Miller Fisher syndrome. The discovery of the GQ1b IgG antibodies in Bickerstaff brainstem encephalitis supported a common autoimmune mechanism in both Bickerstaff brainstem encephalitis and Miller Fisher syndrome (84). In a further study that investigated the role of antibodies against complexes of GQ1b and GT1a, the presence of complex-enhanced or complex-attenuated GQ1b or GT1a antibodies resulted in different binding affinities to the single ganglioside (GQ1b or GT1a), leading to a range of neurologic features (16). In another study utilizing the glycoarray methodology, antibodies to antigens containing GQ1b were detected in 73% of patients with Guillain-Barré syndrome and ophthalmoplegia, 87% of patients with Miller Fisher syndrome, and 74% of patients with Bickerstaff brainstem encephalitis, whereas GD1b-related antibodies were identified in 49% of patients with Guillain-Barré syndrome and ophthalmoplegia, 29.7% of patients with Miller Fisher syndrome, and 11% of patients with Bickerstaff brainstem encephalitis (79). The authors also found that patients with Guillain-Barré syndrome with ophthalmoplegia that were seropositive for both antibodies had a higher probability of requiring artificial ventilation than patients without the antibodies. These findings suggest that the expression of complexes of GQ1b likely differs within the nervous system, resulting in the clinical spectrum that is seen in the anti-GQ1b antibody syndrome.

A large study of patients with Bickerstaff brainstem encephalitis and Miller Fisher syndrome demonstrated that both conditions had many similarities (26). The peripheral nerves were abnormal (most frequently with an absence of the soleus H reflex) in three of four patients with Bickerstaff brainstem encephalitis and 74% of 28 patients with Miller Fisher syndrome. Body sway analyses showed abnormalities within the proprioceptive afferent system in 67% of three patients with Bickerstaff brainstem encephalitis and 72% of 18 of those with Miller Fisher syndrome. In contrast, brain MRI and EEG recordings were abnormal in patients with Bickerstaff brainstem encephalitis (11% and 57%, respectively), as well as some patients with Miller Fisher syndrome (1% and 25%, respectively), suggesting central components can occasionally be affected in both Bickerstaff brainstem encephalitis and Miller Fisher syndrome. GQ1b antibodies were present in 83% of patients with Miller Fisher syndrome (n=466) and 68% of those with Bickerstaff brainstem encephalitis (n= 53). The same study also described patients who did not fulfill the criteria of either Bickerstaff brainstem encephalitis or Miller Fisher syndrome but had GQ1b antibodies. This group of patients was seen to have less extensive clinical features and could represent a forme fruste of either Bickerstaff brainstem encephalitis or Miller Fisher syndrome. These cases did share similar clinical and serological profiles, including the presence of antecedent infections. Referring to such cases as part of the GQ1b antibody syndrome would allow clinicians to classify the syndrome accordingly.

A patient with typical Miller Fisher syndrome or Bickerstaff brainstem encephalitis generally presents with an antecedent episode prior to the onset of their neurologic symptoms. Epidemiological associations between Campylobacter jejuni and Haemophilus influenza infections have been established in patients with Miller Fisher syndrome (31), and a study looking at the serological evidence of infection in patients with Bickerstaff brainstem encephalitis or Miller Fisher syndrome found C jejuni and H influenza to be the two most common pathogens in this group of patients (26; 29; 70; 71). Molecular mimicry whereby the lipo-oligosaccharides of C jejuni isolated from patients with Miller Fisher syndrome or Bickerstaff brainstem encephalitis mimic the GQ1b has been demonstrated (32; 30). Other mimics include the GQ1b-like lipo-oligosaccharide of H influenza isolated from a patient with Miller Fisher syndrome (21). Therefore, it is likely that the infectious agents of patients with Miller Fisher syndrome or Bickerstaff brainstem encephalitis carrying various GQ1b mimics induce the production of GQ1b IgG antibodies, leading to the development of the disease. Following the Zika virus epidemic in Latin America in 2016, there was a rise in the number of patients with Guillain-Barré syndrome. A report of 68 Colombian patients with Zika-associated Guillain-Barré syndrome described two cases with clinical features of Miller Fisher syndrome, expanding the possible microbial associations (56; 73).

Immunohistochemical studies show that GQ1b is highly expressed in the extramedullary regions of the human oculomotor, trochlear, and abducens nerves (07) as compared to other cranial nerves or the ventral and dorsal roots of the spinal cord (08). The neuromuscular junctions may be particularly vulnerable to autoantibody attack as they are outside the blood-nerve barrier. Of note, monoclonal GQ1b antibodies were shown to bind to the vast majority of motor endplates of human oculomotor muscles (41). In an animal model of Miller Fisher syndrome, monoclonal GQ1b antibody plus complement was shown to damage nerve terminals, resulting in the production of mitochondrial hydrogen peroxide that in turn activates Schwann cells (60). Using an in vitro cellular model consisting of co-cultured primary neurons and Schwann cells, the authors found that adenosine triphosphate (ATP) was also released by the injured neurons. The neuron-derived ATP acts as an alarm messenger for Schwann cells, inducing the activation of intracellular pathways and promoting nerve regeneration (59).

Postural body sway analysis results suggest that patients with Miller Fisher syndrome also have a dysfunctional proprioceptive afferent system, and the distinctive sensory ataxia is caused by the selective involvement of muscle spindle afferents (36). These muscle spindles contain specialized muscle fibers, which have motor innervations and are enriched with sensory endings. The neural components and intrafusal muscle fibers of these spindles may be important targets in Miller Fisher syndrome because they have also been labelled by monoclonal GQ1b antibodies in humans (41). The staining pattern suggests that the group 1a afferents in muscle spindles contain GQ1b. Another common neurophysiological finding in patients with Miller Fisher syndrome is an abnormal H-reflex. This finding cannot be explained by involvement of the muscle spindles in isolation (37). It is likely that impairment of the group 1a neurons in the dorsal ganglion also contributes to the ataxia and areflexia (62). In support of this is the finding that GQ1b is also expressed in some large neurons in the human dorsal root ganglia (34). Patients with Miller Fisher syndrome typically show recovery with no sequelae (49); one explanation could be reversible axonopathy of the group 1a fibers due to lengthening of the nodes of Ranvier and myelin splitting with no demyelination features (72).

In Bickerstaff brainstem encephalitis, the characteristic distinguishing clinical feature is altered levels of consciousness that is central in origin. It is postulated that the breakdown of the blood-brain barrier at vulnerable sites, such as the area postrema or blood-nerve barrier at the roots of the oculomotor cranial nuclei, allows access to GQ1b antibodies, which then bind to its related sites within the brainstem reticular formation; however, this course of events has yet to be confirmed. In a study the authors postulated that local or distant neurotoxic effects of endocytosed and retrogradely transported antiganglioside antibodies to the reticular activating system, which lies adjacent to oculomotor nerves in the brainstem, may account for the coma seen in Bickerstaff brainstem encephalitis (11).

The possible mechanism underlying the pathogenesis of Miller Fisher syndrome and Bickerstaff brainstem encephalitis is as follows: (i) infection by a microorganism expressing GQ1b epitope triggers the production of GQ1b antibodies, (ii) these antibodies bind to GQ1b, which are highly expressed on the oculomotor nerves, resulting in acute ophthalmoplegia and group 1a muscle spindles, producing acute ataxic neuropathy. Miller Fisher syndrome develops when both oculomotor nerves and group 1a muscle spindles are affected, and (iii) in some patients, these antibodies can also bind to the reticular formation where GQ1b may be expressed, causing Bickerstaff brainstem encephalitis (83). In a reported review on antiglycolipid antibodies in Guillain-Barré and Miller Fisher syndromes, the authors emphasized the presence of antibodies that specifically recognize a new conformational epitope formed by two different gangliosides (ganglioside complex), which can be detected in some patients with Guillain-Barré or Miller Fisher syndromes (35).

Given good prognostic outcome of Miller Fisher syndrome, there are a few pathological studies available, but it is generally agreed that the pathology in Miller Fisher syndrome is dominantly peripheral (58; 03), whereas overlap syndromes and Bickerstaff encephalitis also have central lesions (46; 53; 26).

Epidemiology

At present, there is little epidemiological information on anti-GQ1b antibody syndrome from large clinical studies. Most epidemiology data have been gleaned from the description of Miller Fisher syndrome as a variant of Guillain-Barré syndrome epidemiology work. One study in an Italian population estimated the annual incidence of Fisher syndrome as 0.9/100000/year (14). Miller Fisher syndrome is reported to have an incidence of approximately 1% to 5% of Guillain-Barré syndrome in Western countries. In a prospective study of 170 Dutch patients with Guillain-Barré syndrome and variant forms, 23 (14%) patients had Miller Fisher syndrome or Miller Fisher-Guillain-Barré overlap syndrome, and two (1%) had Bickerstaff brainstem encephalitis (74). The incidence of Miller Fisher syndrome is appreciably higher in Asian countries such as Taiwan (19%) (43) and Japan (25%) (49). The exact reason for this discrepancy is uncertain, but it raises the possibility that inherent host and environmental factors are likely to play a part.

In a Japanese nationwide survey, the authors estimated an annual incidence of Bickerstaff brainstem encephalitis as 0.078 per 100,000 population, representing 7% of the patients with Guillain-Barré syndrome (33).

A survey on ganglioside antibody positivity during the COVID-19 pandemic, which was performed January 2016 through March 2021, reported that relative to pre-pandemic levels, positivity rates during the pandemic declined by 61% for GQ1b and 24% for GM-1, although remaining unchanged for GD1a and GD1b (57). The authors speculated that mitigation strategies during the pandemic may have reduced the frequency of certain forms of Guillain-Barré syndrome.

Differential diagnosis

Patients with a condition of thiamine deficiency can mimic Bickerstaff brainstem encephalitis, especially when Wernicke encephalopathy develops with ophthalmoplegia, ataxia, and short-term memory loss (which may be interpreted as drowsiness). It is also important to exclude a brainstem stroke in any patient who presents with a fairly acute brainstem syndrome (eg, with ophthalmoplegia, pupillary abnormalities, ataxia, and reduced levels of consciousness). In the acute setting of a stroke, tendon reflexes may appear depressed.

Central demyelinating conditions such as acute disseminated encephalomyelitis and multiple sclerosis can also present with a constellation of brainstem signs that can cause a diagnostic dilemma at first presentation. The presence of ophthalmoplegia along with good recovery of clinical symptoms and signs, including resolution of abnormal lesions on brain imaging, would favor Bickerstaff brainstem encephalitis. In multiple sclerosis, the future course might involve further neurologic symptoms and signs (relapsing remitting form) or a progressive deterioration (primary progressive form).

Neuromuscular junction disorders such as botulism and myasthenia gravis present with ophthalmoplegia. In the former, there is a classic rapid progression from the cranial muscles to the limbs leading to respiratory failure. The presence of additional autonomic features should also alert one to this diagnosis. Myasthenia gravis can be differentiated by the absence of ataxia, areflexia, or drowsiness coupled with muscle fatigability on examination.

Brainstem encephalitis associated with glial or neuronal surface antibodies including NMDA receptor antibodies should be included in a differential diagnosis of anti-GQ1b antibody-positive Bickerstaff brainstem encephalitis (19). It is of interest that one of the three original cases described by Bickerstaff and Cloake in 1951, a young woman who developed seizures, eye movement disorders, and acute psychosis while awaiting ovarian cystectomy, had features that may be more consistent with anti-NMDA receptor encephalitis (47).

The differential diagnosis also includes other inflammatory brainstem lesions such as neuro-Behçet disease, neurosarcoidosis, chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS), CNS vasculitis, as well as infiltrative disorders such as primary brainstem glioma or CNS lymphoma.

In addition, it should be noted that Miller Fisher syndrome or cranial neuropathies can occur as early neurologic manifestations of COVID-19 disease caused by severe acute respiratory coronavirus 2 (SARS-Cov-2) infection without detection of anti-GQ1b antibodies (13; 18; 27; 42). It was also reported that Bickerstaff brainstem encephalitis can develop as a neurologic spectrum of COVID-19 disease (38), but no GQ1b antibodies were detected. It is emphasized that COVID-19 can trigger not only Guillain-Barré syndrome but also other autoimmune neurologic diseases (12). Because GQ1b antibodies have not been identified, a novel antigen might be involved (27). However, a first case of GQ1b antibody-positive Miller Fisher syndrome three weeks after COVID-19 infection was reported (10). GQ1b antibody-positive Miller Fisher syndrome following COVID-19 vaccination has also been reported (01; 51; 78). A review on nine cases of Miller Fisher syndrome following COVID-19 vaccination emphasized that unlike Miller Fisher syndrome following COVID-19 infection, patients with Miller Fisher syndrome following COVID-19 vaccination frequently presented with GQ1b antibody positivity (44% or four out of nine), and Miller Fisher syndrome following COVID-19 vaccination may have a pathophysiology different from Miller Fisher syndrome following COVID-19 infection (28).

Case reports also suggest that Miller Fisher syndrome may develop in association with immunotherapy or cancer therapy, including treatment with ipilimumab and nivolumab (04; 45), cemiplimab (17), or the anti-TNF alfa monoclonal antibody, infliximab (81); however, no anti-GQ1b antibodies were detected in these cases. A case of Bickerstaff brainstem encephalitis that developed after autologous stem cell transplant has also been reported (44).

Diagnostic workup

The diagnostic workup should not only look to support the diagnosis of the anti-GQ1b antibody syndrome, but, when appropriate, should address the differential diagnoses discussed above. Patients who present with features suggestive of a central cause of ataxia and drowsiness with ophthalmoplegia will require brain imaging, preferably MRI, to look for evidence of a vascular, infiltrative, or demyelinating disorder. It should be noted that the MRI can be abnormal in a third of patients with Bickerstaff brainstem encephalitis and 1% of patients with Miller Fisher syndrome, showing increased T2/FLAIR signal in the brainstem, thalamus, cerebellum, cerebrum, or cranial nerves (53; 26; 13). CSF analysis can be normal in Miller Fisher syndrome and its incomplete variants, particularly in the first week of illness, but can also show CSF albuminocytological dissociation. In comparison, the CSF albuminocytological dissociation is less frequent in Bickerstaff brainstem encephalitis (between 35% to 46%) due to a higher frequency of CSF pleocytosis (between 32% to 37%) (53; 26). Electrophysiology in anti-GQ1b antibody syndrome can be normal or show a sensory axonal pattern of neuropathy. The frequency of reduced sensory amplitudes is higher in the median and ulnar nerves compared with the sural nerve (37). In a study, sensory abnormalities were frequently detected in patients, occurring in 94% of patients (67), whereas another group found that an abnormal H-reflex was the most common finding in their patient cohort (65). There have been a handful of case reports of abnormal single fiber electromyography in facial muscles of Miller Fisher patients (37). Electroencephalogram can show slow waves in both Bickerstaff brainstem encephalitis and Miller Fisher syndrome, but it is not likely to be helpful in discriminating them from other encephalopathies.

The most important test that will distinguish this syndrome from other possible diagnoses, as stated above, in the right clinical setting, is the presence of GQ1b IgG antibodies, which are highly specific for any of the disease phenotypes. A case of GQ1b antibody-positive rhombencephalitis caused by Listeria monocytogenes has been reported; however, it remains unknown whether Listeria infection triggered an autoimmune response (87).

Management

There have been no randomized clinical trials of treatment in anti-GQ1b antibody syndrome, including Miller Fisher syndrome or Bickerstaff brainstem encephalitis specifically (55). The decision to treat will depend on the level of disability experienced by patients. Both IVIg and plasma exchange have been used. Although IVIg slightly hastened recovery in Miller Fisher syndrome, the final outcome remained unchanged (48). Bickerstaff brainstem encephalitis also generally has a good prognosis; however, reports of mortality would justify treatment with either IVIg or plasma exchange. In cases where there are also clinical features resembling Guillain-Barré syndrome, treatment with either plasma exchange or IVIg is recommended as randomized controlled trials have established the efficacy of both treatments in Guillain-Barré syndrome (22; 24). The role of steroids in Bickerstaff brainstem encephalitis is less clear, although there have been reports of clinical improvement with steroid administration (61). In Guillain-Barré syndrome, steroids administered on their own were associated with clinical deterioration when compared to no treatment (23).

Along with immunotherapy, supportive treatment such as ventilatory support, tube feeding in patients with swallowing difficulties, prophylaxis against thromboembolic events in patients not able to ambulate, and early rehabilitation are also important.

Outcomes

In Miller Fisher syndrome, patients tend to make a spontaneous recovery. Improvement in ataxia is reported to occur 3 to 41 days after onset, followed closely by improvement in ophthalmoplegia (between 3 and 46 days) (49). The median periods of complete resolution take 32 days in ataxia and 88 days in ophthalmoplegia, respectively (49).

In 13 patients with Miller Fisher syndrome, two out of five (40%) patients treated with intravenous immunoglobulin had residual deficits at six months compared to five out of eight (63%) patients who were left untreated (74).

In Bickerstaff brainstem encephalitis, most patients achieve complete remission by six months, but symptoms of dysesthesia, diplopia, or ataxia may persist in a few patients (53).

Special considerations

Pregnancy

There have been few reports on a case of Miller Fisher syndrome or Bickerstaff brainstem encephalitis in pregnancy. A 26-year-old woman who developed Miller Fisher syndrome at 11 weeks of gestation was reported to have achieved a spontaneous recovery without intervention of any immunotherapy (54).

Anesthesia

No specific precautions are required, and there is no information to suggest added risk of adverse reactions with anesthetic agents.