Autoimmune nodo-paranodopathies of peripheral nerve: the concept is gaining ground

Hereditary nodo-paranodopathies: genomic variants, not just autoantibodies, hit the protein

The scientific commentary refers to ‘Biallelic mutations in neurofascin cause neurodevelopmental impairment and peripheral demyelination’, by Efthymiou et al. (doi:10.1093/brain/awz248).

Anti-pan-neurofascin IgG3 as a marker of fulminant autoimmune neuropathy

Objective

To identify and characterize patients with autoantibodies against different neurofascin (NF) isoforms.

Methods

Screening of a large cohort of patient sera for anti-NF autoantibodies by ELISA and further characterization by cell-based assays, epitope mapping, and complement binding assays.

Results

Two different clinical phenotypes became apparent in this study: The well-known clinical picture of subacute-onset severe sensorimotor neuropathy with tremor that is known to be associated with IgG4 autoantibodies against the paranodal isoform NF-155 was found in 2 patients. The second phenotype with a dramatic course of disease with tetraplegia and almost locked-in syndrome was associated with IgG3 autoantibodies against nodal and paranodal isoforms of NF in 3 patients. The epitope against which these autoantibodies were directed in this second phenotype was the common Ig domain found in all 3 NF isoforms. In contrast, anti–NF-155 IgG4 were directed against the NF-155–specific Fn3Fn4 domain. The description of a second phenotype of anti–NF-associated neuropathy is in line with some case reports of similar patients that were published in the last year.

Conclusions

Our results indicate that anti–pan-NF-associated neuropathy differs from anti–NF-155-associated neuropathy, and epitope and subclass play a major role in the pathogenesis and severity of anti–NF-associated neuropathy and should be determined to correctly classify patients, also in respect to possible differences in therapeutic response.

Anti-CNTN1 IgG3 induces acute conduction block and motor deficits in a passive transfer rat model

Background

Autoantibodies against the paranodal protein contactin-1 have recently been described in patients with severe acute-onset autoimmune neuropathies and mainly belong to the IgG4 subclass that does not activate complement. IgG3 anti-contactin-1 autoantibodies are rare, but have been detected during the acute onset of disease in some cases. There is evidence that anti-contactin-1 prevents adhesive interaction, and chronic exposure to anti-contactin-1 IgG4 leads to structural changes at the nodes accompanied by neuropathic symptoms. However, the pathomechanism of acute onset of disease and the pathogenic role of IgG3 anti-contactin-1 is largely unknown.

Methods

In the present study, we aimed to model acute autoantibody exposure by intraneural injection of IgG of patients with anti-contacin-1 autoantibodies to Lewis rats. Patient IgG obtained during acute onset of disease (IgG3 predominant) and IgG from the chronic phase of disease (IgG4 predominant) were studied in comparison.

Results

Conduction blocks were measured in rats injected with the “acute” IgG more often than after injection of “chronic” IgG (83.3% versus 35%) and proved to be reversible within a week after injection. Impaired nerve conduction was accompanied by motor deficits in rats after injection of the “acute” IgG but only minor structural changes of the nodes. Paranodal complement deposition was detected after injection of the “acute IgG”. We did not detect any inflammatory infiltrates, arguing against an inflammatory cascade as cause of damage to the nerve. We also did not observe dispersion of paranodal proteins or sodium channels to the juxtaparanodes as seen in patients after chronic exposure to anti-contactin-1.

Conclusions

Our data suggest that anti-contactin-1 IgG3 induces an acute conduction block that is most probably mediated by autoantibody binding and subsequent complement deposition and may account for acute onset of disease in these patients. This supports the notion of anti-contactin-1-associated neuropathy as a paranodopathy with the nodes of Ranvier as the site of pathogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1462-z) contains supplementary material, which is available to authorized users.

Increased IP-10 production by blood-nerve barrier in multifocal acquired demyelinating sensory and motor neuropathy and multifocal motor neuropathy

OBJECTIVE

Dysfunction of the blood-nerve barrier (BNB) plays important roles in chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN). The aim of the present study was to identify the candidate cytokines/chemokines that cause the breakdown of the BNB using sera from patients with CIDP and MMN.

METHODS

We determined the levels of 27 cytokines and chemokines in human peripheral nerve microvascular endothelial cells (PnMECs) after exposure to sera obtained from patients with CIDP variants (typical CIDP and multifocal acquired demyelinating sensory and motor neuropathy [MADSAM]), MMN and amyotrophic lateral sclerosis (ALS), and healthy controls (HC), using a multiplexed fluorescent bead-based immunoassay system.

RESULTS

The induced protein (IP)10 level in the cells in both the MADSAM and MMN groups was markedly increased in comparison with the typical CIDP, ALS and HC groups. The other cytokines, including granulocyte colony-stimulating factor,vascular endothelial growth factor (VEGF) and interleukin-7, were also significantly upregulated in the MADSAM group. The increase of IP-10 produced by PnMECs was correlated with the presence of conduction block in both the MADSAM and MMN groups.

CONCLUSION

The autocrine secretion of IP-10 induced by patient sera in PnMECs was markedly upregulated in both the MADSAM and MMN groups. The overproduction of IP-10 by PnMECs leads to the focal breakdown of the BNB and may help to mediate the transfer of pathogenic T cells across the BNB, thereby resulting in the appearance of conduction block in electrophysiological studies of patients with MADSAM and MMN.

Anti-Neurofascin-155 IgG4 antibodies prevent paranodal complex formation in vivo

Neurofascin-155 (Nfasc155) is an essential glial cell adhesion molecule expressed in paranodal septate-like junctions of peripheral and central myelinated axons. The genetic deletion of Nfasc155 results in the loss of septate-like junctions and in conduction slowing. In humans, IgG4 antibodies against Nfasc155 are implicated in the pathogenesis of chronic inflammatory demyelinating polyneuropathy (CIDP). These antibodies are associated with an aggressive onset, a refractoriness to intravenous immunoglobulin, and tremor of possible cerebellar origin. Here, we examined the pathogenic effects of patient-derived anti-Nfasc155 IgG4. These antibodies did not inhibit the ability of Nfasc155 to complex with its axonal partners contactin-1/CASPR1 or induce target internalization. Passive transfer experiments revealed that IgG4 antibodies target Nfasc155 on Schwann cell surface, and diminished Nfasc155 protein levels and prevented paranodal complex formation in neonatal animals. In adult animals, chronic intrathecal infusions of antibodies also induced the loss of Nfasc155 and of paranodal specialization and resulted in conduction alterations in motor nerves. These results indicate that anti-Nfasc155 IgG4 perturb conduction in absence of demyelination, validating the existence of paranodopathy. These results also shed light on the mechanisms regulating protein insertion at paranodes.

Chronic immune sensorimotor polyradiculopathy: Report of a case series

INTRODUCTION

Chronic immune sensorimotor polyradiculopathy (CISMP) is a chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) variant affecting both sensory and motor nerve roots without evidence of peripheral nerve demyelination.

METHODS

We report a case series of 9 patients with CISMP, identified from 2 tertiary centers. Clinical, electrodiagnostic, and neuroradiologic features, and treatment responses, were retrospectively reviewed.

RESULTS

Patients presented with sensorimotor deficits and hypo-/areflexia, predominantly involving lower extremities. Three had cranial nerve involvement. Electrodiagnostic findings in all patients localized to roots proximal to dorsal root ganglia, without evidence of peripheral nerve demyelination. Cerebrospinal fluid examination revealed an albuminocytologic association. Eight patients exhibited gadolinium enhancement and thickening of multiple spinal nerve roots and/or cranial nerves. All patients demonstrated good responses to immunotherapies.

DISCUSSION

CISMP is similar to CIDP in many aspects, but lacks typical electrodiagnostic findings of peripheral nerve demyelination. It is important to recognize this unusual and treatable entity. Muscle Nerve 59:658-664, 2019.

Guillain-Barré Syndrome

Guillain-Barré syndrome (GBS) is an acute immune-mediated polyradiculoneuropathy, and pathophysiologically classified into acute inflammatory demyelinating polyneuropathy (AIDP), acute motor axonal neuropathy (AMAN), and acute motor and sensory axonal neuropathy (AMSAN). The main pathophysiological mechanism is complement-mediated nerve injury caused by antibody-antigen interaction in the peripheral nerves. Antiglycolipid antibodies are most pathogenic factors in the development of GBS, but not found in 40% of patients with GBS. One of the principal target regions in GBS is the node of Ranvier where functional molecules including glycolipids are assembled. Nodal dysfunction induced by the immune response in nodal axolemma, termed "nodopathy," can electrophysiologically show reversible conduction failure, axonal degeneration, or segmental demyelination. To detect new target molecules in antiglycolipid antibody-negative GBS and to elucidate the pathophysiology in the subacute and the subsequent phases of the disorder are the next problems.

The electrodiagnosis of Guillain-Barré syndrome subtypes: Where do we stand?

It is controversial as to whether the electrophysiological Guillain-Barré syndrome (GBS) subtypes can be diagnosed on the basis of a single study and which criteria sets and cut-offs should be used. Serial electrophysiologic studies have shown that a significant number of patients changed electrodiagnostic subtype largely because of the recognition of reversible conduction failure as a possible evidence of axonal pathology. However, other reports concluded that electrodiagnosis can be made by a single study, the subtypes depending on the characteristic of the criteria set applied. Such divergent views, although explicable by the different methodology employed, can be confusing in the everyday practice. We argue that the pathophysiology of GBS is dynamic and that serial studies allow a more accurate diagnosis of subtypes. A second study, although not always practicable, is recommended in patients showing no clear demyelinating features, low amplitude distal compound muscle action potentials or conduction block without temporal dispersion. For practical purposes, we propose that at a first study Uncini's or Rajabally's criteria sets can be employed for an indicative subtype diagnosis. Finally, although the GBS subtype diagnosis has currently no impact on treatment, we believe that is important for understanding the underlying pathophysiology and prognostication.

Reversible conduction failure on the deep tendon reflex response recording in early Guillain-Barré syndrome

Objective

To describe the case of a patient with Guillain-Barré syndrome (GBS) showing early reversible conduction failure (RCF) detected by means of serial deep tendon reflex response (T-reflex) study.

Methods

A 36-year-old woman had a 5-day history of foot and hand paresthesias ascending to thighs and arms, throbbing interscapular and neck pain, mild to moderate tetraparesis, and areflexia. Nerve conduction studies (NCS) were performed on days 7 and 33 after onset.

Results

NCS showed an equivocal electrophysiologic pattern, just an isolated distal RCF being detected on the right radial nerve at initial examination. Motor latency on deltoid muscle after Erb's point stimulation was preserved. Sensory conduction velocities were normal or slightly slowed. Somatosensory evoked potentials from median and tibial nerves were normal. Initially, F-wave study demonstrated reversible abnormalities, consisting of multiple A waves and low F-wave persistence, minimal F-wave latencies being preserved. Biceps brachii T-reflex was normal, whereas Achilles T-reflex was absent bilaterally, appearing on the second study with normal T-wave morphology and latency, thus conforming to the requirements for RCF diagnosis. Soleus H-reflex was also initially absent.

Conclusions

Serial T-reflex study is a useful technique for detecting early RCF of proximal nerve trunks in early GBS.

Significance

T-reflex is useful tool for GBS in association with NCS.

Immune-mediated neuropathies

Since the discovery of an acute monophasic paralysis, later coined Guillain-Barré syndrome, almost 100 years ago, and the discovery of chronic, steroid-responsive polyneuropathy 50 years ago, the spectrum of immune-mediated polyneuropathies has broadened, with various subtypes continuing to be identified, including chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN). In general, these disorders are speculated to be caused by autoimmunity to proteins located at the node of Ranvier or components of myelin of peripheral nerves, although disease-associated autoantibodies have not been identified for all disorders. Owing to the numerous subtypes of the immune-mediated neuropathies, making the right diagnosis in daily clinical practice is complicated. Moreover, treating these disorders, particularly their chronic variants, such as CIDP and MMN, poses a challenge. In general, management of these disorders includes immunotherapies, such as corticosteroids, intravenous immunoglobulin or plasma exchange. Improvements in clinical criteria and the emergence of more disease-specific immunotherapies should broaden the therapeutic options for these disabling diseases.

Diagnostic insights into chronic-inflammatory demyelinating polyneuropathies

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a rare immune-mediated neuropathy with demyelination of nerve fibers as leading morphological feature. The course of disease can be chronic progressive or remitting relapsing. Whereas for acute immune-mediated neuropathies several serological markers have been identified and used successfully in clinical routine, the serological diagnosis of chronic variants such as CIDP has not yet been evolved satisfactory. The typical CIDP and its various atypical variants are characterized by a certain diversity of clinical phenotype and response to treatment. Thus, diagnostic markers could aid in the differential diagnosis of CIDP variants and stratification of patients for a better treatment response. Most patients respond well to a causal therapy including steroids, intravenous immunoglobulins and plasmapheresis. Apart from electrophysiological and morphological markers, several autoantibodies have been reported as candidate markers for CIDP, including antibodies against glycolipids or paranodal/nodal molecules. The present review provides a summary of the progress in autoantibody testing in CIDP and its possible implication on the stratification of the CIDP variants and treatment response.

Miller Fisher syndrome, Bickerstaff brainstem encephalitis and Guillain-Barré syndrome overlap with persistent non-demyelinating conduction blocks: a case report

Background

Miller Fisher syndrome (MFS) and Bickerstaff’s Brainstem Encephalitis (BBE) share some clinical features and a common immunological profile characterized by anti-GQ1b antibodies. Some MFS patients overlap with Guillain-Barré syndrome (GBS) or BBE. We report a patient with MFS, BBE, and axonal GBS overlap in whom serial electrophysiological studies showed persistent motor conduction blocks (CBs).

Case presentation

A 61-year-old man acutely developed ophtalmoparesis, ataxia and areflexia suggesting MFS. Paresthesias, severe weakness, and drowsiness rapidly developed indicating an overlap with BBE and GBS. Preceding infection with Mycoplasma Pneumoniae and anti-GQ1b antibodies were detected. On day 4, nerve conduction study showed reduced or non-recordable compound muscle action potentials (CMAPs) and sensory nerve action potentials (SNAPs) without demyelinating features, indicating the electrodiagnosis of acute motor and sensory axonal neuropathy and suggesting a poor prognosis. Intravenous immunoglobulins (IVIg) were given but clinical status worsened to ophthalmoplegia, tetraplegia and coma needing mechanical ventilation. A second IVIg course was given and the patient was weaned off ventilation on day 41 and transferred to rehabilitation on day 57 with partial resolution of the ophthalmoplegia and limited recovery of muscle strength. Electrophysiology showed, after 10 weeks, greatly improved distal CMAP amplitudes suggesting the resolution of distal CBs while CBs in intermediate and proximal nerve segments emerged. CBs unusually persisted for four to 6 months without development of abnormal temporal dispersion. A third IVIg course was started on day 179 and the resolution of CBs mirrored the clinical improvement.

Conclusions

GQ1b gangliosides are expressed in the nodal region of oculomotor nerves, muscle spindle afferents, peripheral nerves and possibly in the brainstem reticular formation. Anti-GQ1b antibodies may explain the complex symptomatology and the overlap between MFS, BBE, and GBS.

CBs that persisted and recovered without the development of temporal dispersion suggest that weakness was due to a sustained, antibody-mediated, attack at the nodal region inducing a non-demyelinating conduction failure as expression of an acute onset, long lasting, nodopathy. Serial electrophysiological studies allowed not only to understand the underlying pathophysiology and formulate a more correct prognosis but also to guide the treatment.