Double agents and breakdown of integrity at the neuromuscular junction in Miller-Fisher syndrome

GQ1b antibody testing in Guillain-Barre syndrome and variants

Guillain-Barre syndrome (GBS) is characterized by an ascending muscle paralysis with progressive loss of muscle stretch reflexes. Annually, approximately 2.4 cases per 100,000 population of GBS are reported. Variant forms do exist. These include the Fisher syndrome, GBS with ophthalmoplegia, Bickerstaff's brainstem encephalitis (BBE), and acute ophthalmoparesis without ataxia. In the last 15 years, attention has been directed towards the association of the GQ1b IgG antibody and several GBS variants, particularly the Fisher syndrome and those associated with ophthalmoparesis. We present three cases of GBS variants. All three cases had associated ophthalmoplegia but only one of the three had a positive GQ1b antibody association.

Recent developments in Miller Fisher syndrome and related disorders

PURPOSE OF REVIEW

Miller Fisher syndrome is a localized variant of Guillain-Barré syndrome, characterized by ophthalmoplegia, areflexia and ataxia. Bickerstaff's brainstem encephalitis is a related syndrome in which upper motor neurone features accompany the classic triad. Anti-GQ1b antibodies are uniquely found in both conditions and are believed to be pathogenic.

RECENT FINDINGS

Infectious illnesses usually precede Miller Fisher syndrome. The clearest associations have been described with Haemophilus influenzae and Campylobacter jejuni infection. Raised cerebrospinal fluid protein is seen in 60% of patients, but clinical features and anti-GQ1b antibody testing are diagnostically more informative. Experimental studies demonstrating complement-dependent neuromuscular block may be relevant to the clinical pathophysiology of Miller Fisher syndrome. Recent neurophysiological studies suggest abnormal neuromuscular transmission occurs in some cases of Miller Fisher syndrome and Guillain-Barré syndrome. Recent mouse models have demonstrated that presynaptic neuronal membranes and perisynaptic Schwann cells are targets for anti-GQ1b antibody attack. The elimination of antiganglioside antibodies from the circulation through specific immunoadsorption therapy has the potential to ameliorate the course of Miller Fisher syndrome. This condition is typically a benign, self-limiting illness. Both plasmapheresis and intravenous immunoglobulin may be employed as treatment, especially in cases of Bickerstaff's brainstem encephalitis or those with overlapping Guillain-Barré syndrome.

SUMMARY

Anti-GQ1b antibody testing has allowed clinicians to develop a greater understanding of the spectrum of Miller Fisher syndromes and to refine clinical diagnoses in patients with unusual presentations. Experimental studies strongly suggest anti-GQ1b antibodies are pathogenic, which in principle should direct treatments towards antibody neutralization or elimination.

Anti-GM1 antibodies: the cause of otherwise unexplained ophthalmoplegias?

PURPOSE

To report four patients with otherwise unexplained ophthalmoplegia who were found to have elevated levels of anti-GM1 antibodies.

METHODS

Retrospective chart evaluation of 50 consecutive patients with otherwise unexplained ophthalmoparesis. All patients were tested for anti-GM1 antibodies.

RESULTS

Six out of 50 cases (12%) were found to have elevated anti-GM1 antibodies, far greater than the 2.7% found in the general population. Four of the subjects with elevated anti-GM1 antibodies are reported.

CONCLUSION

Although the mechanism and relationship between the neural antibodies and ophthalmoparesis is not understood, it is proposed that the presence of anti-GM1 antibodies should be considered in cases of otherwise unexplained ophthalmoplegia.

Acute ophthalmoparesis in the anti-GQ1b antibody syndrome: electrophysiological evidence of neuromuscular transmission defect in the orbicularis oculi

OBJECTIVE

To prospectively study anti-GQ1b antibody positive cases of acute ophthalmoparesis (AO) clinically and electrophysiologically.

METHODS

Nine consecutive cases presenting with predominantly acute ophthalmoplegia were assessed clinically and had stimulated single fibre electromyography (SFEMG) of the orbicularis oculi at presentation. All had magnetic resonance imaging brain scans and anti-GQ1b antibody titres determined.

RESULTS

Four cases had elevated anti-GQ1b antibody titres and abnormal SFEMG studies, which improved in tandem with clinical recovery over three months. Five other anti-GQ1b antibody negative cases were diagnosed as diabetic related cranial neuropathy, idiopathic cranial neuropathy, ocular myasthenia gravis, and Tolosa-Hunt syndrome. All five cases showed complete recovery over a three month period.

CONCLUSIONS

This study demonstrated electrophysiologically the dynamic improvement of neuromuscular transmission of anti-GQ1b antibody positive cases of AO, in tandem with clinical recovery. SFEMG is of value in differentiating weakness due to neuromuscular transmission defect from neuropathy in these clinical situations.

Differential blocking effects of the monoclonal anti-GQ1b IgM antibody and alpha-latrotoxin in the absence of complement at the mouse neuromuscular junction

Numerous in vitro electrophysiological studies found different effects of anti-ganglioside antibodies on neuromuscular transmission. Since a complement-dependent, latrotoxin-like effect has been described for the mouse monoclonal anti-GQ1b IgM antibody (termed CGM3), we here investigated the effect of CGM3 and alpha-latrotoxin by means of the perfused macro-patch clamp electrode in mice hemidiaphragms in the absence of complement. The CGM3 mab depressed evoked quantal release dose-dependently, whereas the rate of spontaneous releases and the amplitude of postsynaptic currents was not significantly affected. Alpha-latrotoxin induced an increase in spontaneous releases followed by a blockade of evoked quantal release, this was not altered by CGM3. The complement-independent presynaptic block by CGM3 was different from the action of alpha-latrotoxin.

Progress in Guillain-Barré syndrome

This editorial review summarizes and critically analyses reports published in the preceding 18 months on the pathogenesis of Guillain-Barré syndrome, with particular emphasis on the role of ganglioside antibodies, antecedent infections, and the concept of molecular mimicry. It concludes with an appraisal of currently available and proposed therapies.