Antiganglioside antibodies do not necessarily play a role in multifocal motor neuropathy

Peripheral Neuropathy

Peripheral neuropathy is a commonly encountered disorder in clinical practice. In light of an aging population and the diabetes and obesity pandemic, the prevalence of peripheral neuropathy is increasing, posing a significant public health concern. This article provides a diagnostic framework for neuropathies and summarizes treatment options.

Clinical neurophysiology of anterior horn cell disorders

The development of neurophysiological techniques for clinical assessment in the 20th century is closely related to the study of anterior horn cell diseases. The effects of motor axon loss on nerve conduction velocity and compound motor amplitude were elucidated first in amyotrophic lateral sclerosis (ALS), as was the characterization of reinnervation as detected by needle electromyography. The same changes noted in early studies still play a major role in the diagnosis of anterior horn cell diseases. In addition, much of modern neurophysiological assessment of motor axon quantitation, ion channel changes in neurogenic disease, and cortical physiology studies to assess both network and excitability abnormalities have all been applied to ALS. In this chapter, we summarize the clinical attributes of ALS and Spinal Muscular Atrophy, and review how clinical neurophysiology is employed in the clinical and the research setting.

Nerve ultrasound as follow-up tool in treated multifocal motor neuropathy

BACKGROUND AND PURPOSE

High-resolution ultrasound is a valuable tool in supporting the diagnosis of multifocal motor neuropathy (MMN) but longitudinal data under therapy are lacking.

METHODS

The change in peripheral nerve ultrasound pattern in patients with MMN was assessed over time. Patients with MMN received a thorough initial examination and follow-up over a period of 6-12 months using high-resolution ultrasound of the cervical roots and the nerves of the arms and legs, nerve conduction studies, Medical Research Council Sum Score (MRCSS) and Rotterdam Inflammatory Neuropathy Cause and Treatment Group (INCAT) score to evaluate changes under treatment. The Ultrasound Pattern Sum Score (UPSS) was used as standardized peripheral nerve ultrasound protocol.

RESULTS

Seventeen patients with MMN received initial examinations of whom 12 were successfully followed up. All patients with MMN showed at least localized but often multifocal peripheral nerve enlargement. An enlarged overall cross-sectional area as well as enlarged single fascicles (>3 mm²) in clinically and electrophysiologically affected (>90%) and unaffected (>70%) nerves were found. The UPSS did not correlate with clinical disability at both visits. However, the change in clinical disability (evaluated as difference in MRCSS) and the change in UPSS correlated significantly inversely (P = 0.004).

CONCLUSIONS

High-resolution sonography of peripheral nerves revealed multifocal nerve enlargement in MMN. Distinct enlargement patterns may support the diagnosis. Ultrasound findings did not correlate well with clinical severity or electrophysiological findings at initial presentation. As changes in UPSS correlated significantly with the clinical course in terms of muscle strength (MRCSS), sonographic assessment may represent a useful tool for therapeutic monitoring.

Cerebrospinal fluid findings in Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathies

The classic immunologic alteration of the cerebrospinal fluid (CSF) in Guillain-Barré syndrome (GBS), albuminocytologic dissociation, has been known since the original paper by Guillain, Barré, and Strohl. Albuminocytologic dissociation has been also described in other forms of the GBS spectrum, such as axonal motor or motor-sensory forms (AMAN, AMSAN), the anti-GQ1b spectrum of Miller Fisher syndrome, and Bickerstaff brainstem encephalitis. Cytokines, chemokines, antibodies, complement components, and molecules with a putative neuroprotective role or indicating axonal damage have also been examined using different methods. Besides these candidate approaches, proteomics has been recently applied to discover potential biomarkers. The overall results support the immunopathogenesis of GBS, but albuminocytologic dissociation remained the only consistent CSF biomarker supporting the diagnosis of GBS. Chronic inflammatory neuropathies also comprise a heterogeneous group of diseases. Increased protein in the CSF is a supportive factor of chronic inflammatory demyelinating polyneuropathy, especially in the absence of definite electrophysiologic criteria. A number of other markers have also been investigated in the CSF of patients with chronic inflammatory neuropathies, similar to GBS. However, none has been used in supporting diagnosis, differentiating among syndromes, or predicting the clinical course and treatment responses.

Acquired immune demyelinating neuropathies

PURPOSE OF REVIEW

Acquired immune demyelinating neuropathies refer to a group of disorders that share overlapping sensory, motor, and autonomic clinical, laboratory, and electrodiagnostic features. It is important to recognize acquired immune demyelinating neuropathies as they are generally responsive to immunosuppressive or immunomodulatory therapies.

RECENT FINDINGS

This article reviews recently developed early prognostic tools in Guillain-Barré syndrome and discusses the evolving understanding of chronic demyelinating phenotypes with differing treatment responsiveness.

SUMMARY

While weakness and numbness progress over 2 to 4 weeks in Guillain-Barré syndrome, they continue to evolve beyond 8 weeks in chronic inflammatory demyelinating polyradiculoneuropathy and over 4 to 8 weeks in subacute inflammatory demyelinating polyradiculoneuropathy. Acquired immune demyelinating neuropathies present uncommonly as variants with predominance of ocular, bulbar, sensory, autonomic, or motor manifestations in addition to regional variants, such as paraparetic acquired immune demyelinating neuropathies. Establishing the correct diagnosis is important as these immune disorders differ in response to corticosteroids and other immunosuppressive therapies.

Multifocal motor neuropathy, multifocal acquired demyelinating sensory and motor neuropathy, and other chronic acquired demyelinating polyneuropathy variants

Chronic acquired demyelinating neuropathies (CADP) constitute an important group of immune neuromuscular disorders affecting myelin. This article discusses CADP with emphasis on multifocal motor neuropathy, multifocal acquired demyelinating sensory and motor neuropathy, distal acquired demyelinating symmetric neuropathy, and less common variants. Although each of these entities has distinctive laboratory and electrodiagnostic features that aid in their diagnosis, clinical characteristics are of paramount importance in diagnosing specific conditions and determining the most appropriate therapies. Knowledge regarding pathogenesis, diagnosis, and management of these disorders continues to expand, resulting in improved opportunities for identification and treatment.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) was first described in 1988 as a purely motor neuropathy affecting multiple motor nerves. The diagnosis was based entirely on demonstrating electrophysiological evidence of a conduction block (CB) that selectively affected motor axons, with sparing of sensory axons even through the site of motor CB. Subsequently, a similar disorder was reported but with absence of demonstrable CB on routine nerve conduction studies and there is still some debate as to whether MMN without CB is related to MMN. MMN is thought to be an inflammatory neuropathy related to an immune attack on motor nerves. The conventional hypothesis is that the primary pathology is segmental demyelination, but recent research raises the possibility of a primary axonopathy. Anti-GM1 antibodies can be found in some patients but it is unclear whether these antibodies are pathogenic. Intravenous immunoglobulin is the mainstay of treatment but other immunosuppressive treatments can also be effective.

Anti-GM1 antibodies as a model of the immune response to self-glycans

Glycans are a class of molecules with high structural variability, frequently found in the plasma membrane facing the extracellular space. Because of these characteristics, glycans are often considered as recognition molecules involved in cell social functions, and as targets of pathogenic factors. Induction of anti-glycan antibodies is one of the early events in immunological defense against bacteria that colonize the body. Because of this natural infection, antibodies recognizing a variety of bacterial glycans are found in sera of adult humans and animals. The immune response to glycans is restricted by self-tolerance, and no antibodies to self-glycans should exist in normal subjects. However, antibodies recognizing structures closely related to self-glycans do exist, and can lead to production of harmful anti-self antibodies. Normal human sera contain low-affinity anti-GM1 IgM-antibodies. Similar antibodies with higher affinity or different isotype are found in some neuropathy patients. Two hypotheses have been developed to explain the origin of disease-associated anti-GM1 antibodies. According to the "molecular mimicry" hypothesis, similarity between GM1 and Campylobacter jejuni lipopolysaccharide carrying a GM1-like glycan is the cause of Guillain-Barré syndrome associated with anti-GM1 IgG-antibodies. According to the "binding site drift" hypothesis, IgM-antibodies associated with disease originate through changes in the binding site of normally occurring anti-GM1 antibodies. We now present an "integrated" hypothesis, combining the "mimicry" and "drift" concepts, which satisfactorily explains most of the published data on anti-GM1 antibodies.

Antibody testing in peripheral neuropathies

Many autoantibodies have been described in association with peripheral neuropathy, but the use of antibody testing in clinical practice remains a matter of some debate. Serum autoantibodies to gangliosides or glycoproteins are implicated in a variety of sensory and motor neuropathy syndromes. Paraneoplastic antibodies help identify patients who have a neuropathy related to an underlying malignancy. Detection of an autoantibody in the right clinical setting provides some evidence that the peripheral nerve disturbance is immune mediated and that immunomodulatory therapy may be of benefit.

Multifocal motor neuropathy: current concepts and controversies

Multifocal motor neuropathy (MMN) is now a well-defined purely motor multineuropathy characterized by the presence of multifocal partial motor conduction blocks (CB), frequent association with anti-GM1 IgM antibodies, and usually a good response to high-dose intravenous immunoglobulin (IVIg) therapy. However, several issues remain to be clarified in the diagnosis, pathogenesis, and therapy of this condition including its nosological position and its relation to other chronic dysimmune neuropathies; the degree of CB necessary for the diagnosis of MMN; the existence of an axonal form of MMN; the pathophysiological basis of CB; the pathogenetic role of antiganglioside antibodies; the mechanism of action of IVIg treatments in MMN and the most effective regimen; and the treatment to be used in unresponsive patients. These issues are addressed in this review of the main clinical, electrophysiological, immunological, and therapeutic features of this neuropathy.

Serum IgM anti-GM1 ganglioside antibodies in lower motor neuron syndromes

Lower motor neuron syndromes (LMNS) are heterogenous conditions, which include patients with progressive lower motor neuron disease (LMND) and cases with the clinical phenotype of motor neuropathy (MN). The aim of this study was to estimate the IgM anti-GM1 ganglioside antibodies titer and the ratio of the light chains in order to define the presence of autoimmunity process in particular cases with LMNS. Twenty-eight patients were diagnosed with LMND and 15 patients were diagnosed with MN (10 patients with multifocal motor neuropathy with conduction block, five patients with MN without conduction block). Total of 103 patients with classical amyotrophic lateral sclerosis (ALS) and 50 healthy, age-matched persons were also tested. The IgM anti-GM1 ganglioside titer and the ratio of lambda/kappa light chains in serum were determined using the ELISA technique. High titer of IgM anti-GM1 antibodies were detected in serum of 46% LMND patients, 80% of MN patients, and 18% of the classical ALS cases. An elevated ratio of lambda/kappa light chains appeared in 18% of LMND patients, and in 67% of the MN cases. The lambda/kappa light chains ratio was normal in all ALS patients. The presence of elevated titer of IgM anti-GM1 ganglioside antibodies and the changed ratio of the light chains supports the presence of autoimmune process in LMNS and may provide clues for their management.

The origin of anti-GM1 antibodies in neuropathies: the "binding site drift" hypothesis

Elevated titers of serum antibodies against GM1-ganglioside are associated with a variety of autoimmune neuropathies. The origin of these autoantibodies is still unknown, although there is evidence that they are produced by CD5+ B-lymphocytes and that antigen mimicry is involved. Anti-GM, IgM-antibodies in the normal human immunological repertoire are low affinity antibodies that cross-react with other glycoconjugates carrying Gal beta1-3GalNAc and probably do not have GM1-mediated biological activity. Other anti-GM1 IgM-antibodies with higher affinity and/or different fine specificity are present in patients with motor syndromes. Based on our studies of structural requirement for binding, we hypothesize that disease-associated anti-GM1 antibodies originate at random by mutations affecting the binding site of naturally-occurring ones. The hypothesis is conceptually similar to the established phenomenon of "genetic drift" in species evolutionary biology and is therefore termed "binding site drift".

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a recently identified peripheral nerve disorder characterized by progressive, predominantly distal, asymmetric limb weakness mostly affecting upper limbs, minimal or no sensory impairment, and by the presence on nerve conduction studies of multifocal persistent partial conduction blocks on motor but not sensory nerves. The etiopathogenesis of MMN is not known, but there is some evidence, based mostly on the clinical improvement after immunological therapies, that the disease has an immunological basis. Antibodies, mostly IgM, to the gangliosides GM1, and though less frequently, GM2 and GD1a, are frequently detected in patients' sera, helping in the diagnosis of this disease. Even if there is some experimental evidence that these antibodies may be pathogenic in vitro, their role in the neuropathy remains to be established. Patients with MMN do not usually respond to steroids or plasma exchange, which may occasionally worsen the symptoms, while the efficacy of cyclophosphamide is limited by its relevant side effects. More than 80% of MMN patients rapidly improve with high dose intravenous immunoglobulin therapy (IVIg). The effect of this therapy is, however, transient and improvement has to be maintained with periodic infusions. A positive response to interferon-beta has been recently reported in a minority of patients, some of whom were resistant to IVIg. Even if many progresses have been made on the diagnosis and therapy of MMN, there are still several issues on the nosological position, etiopathogenesis and long-term treatment of this neuropathy that need to be clarified.

Asymmetric Acquired Demyelinating Polyneuropathies: MMN and MADSAM

More than a half a century after Austin's initial description of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the clinical spectrum of chronic acquired demyelinating polyneuropathies has expanded. Currently there are a number of entities that can be put under the heading of chronic acquired demyelinating neuropathy (CADP) based on differing clinical presentations. In this scheme, CIDP is used only to refer to patients with demyelinating neuropathies and generalized symmetric weakness. In contrast, multifocal motor neuropathy (MMN) and multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) fall into the category of asymmetrical, multifocal forms of CADP. These are distinguished from each other only by the presence of sensory involvement. In our opinion, there are pragmatic reasons for splitting these clinical presentations into distinct entities. Although each of these clinical subtypes shares some basic similarities, there are important differences. MMN is usually considered resistant to corticosteroid therapy and the first line agent in this disorder is intravenous immunoglobulin (IVIg). MADSAM neuropathy can be responsive to prednisone or IVIg, and has a profile more analogous to classic CIDP with regards to its laboratory features and treatment response.

Clinical spectrum of chronic acquired demyelinating polyneuropathies

A number of presentations of chronic demyelinating polyneuropathy have been identified, each distinguished by its phenotypic pattern. In addition to classic chronic inflammatory demyelinating polyneuropathy (CIDP), which is characterized clinically by symmetric proximal and distal weakness and sensory loss, several regional variants can be recognized: multifocal motor neuropathy (MMN: asymmetric and pure motor), multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy (asymmetric, sensory, and motor), and distal acquired demyelinating symmetric (DADS) neuropathy (symmetric, distal, sensory, and motor). There are also temporal, pathological, and disease-associated variants. This review describes a clinical scheme for approaching the chronic acquired demyelinating polyneuropathies that leads to a rational use of supportive laboratory studies and treatment options. In addition, we propose new diagnostic criteria for CIDP that more accurately reflect current clinical practice.

Anti-GM1 antibodies can block neuronal voltage-gated sodium channels

Anti-GM1 antibodies, frequently found in the serum of patients with Guillain-Barré syndrome (GBS), have been suggested to interfere with axonal function. We report that IgG anti-GM1 antibodies, raised in rabbits, can reversibly block the voltage-gated Na(+) channels of nerve cells, thus causing a reduction of the excitatory Na(+) current. The block was, however, only substantial when the antibodies were applied together with rabbit complement factors. A solution containing anti-GM1 sera (dilution 1:100) and complement (1:50) reduced the Na(+) current to 0.5 +/- 0.2 times control (mean value +/- SD). Applications of the antibody by itself, complement by itself, or anti-GM2 or anti-GM4 antibodies (1:100) plus complement had little effect. The complexes of anti-GM1 antibodies and complement factors block the ion-conducting pore of the channel directly. In addition, they increase the fraction of channels that are inactivated at the resting potential and alter channel function by changing the membrane surface charge. The described effects may be responsible for conduction slowing and reversible conduction failure in some GBS patients.

Use of human intravenous immunoglobulin in lower motor neuron syndromes

OBJECTIVE

To determine whether patients with the clinical phenotype of multifocal motor neuropathy but without the electrophysiological criteria for conduction block would respond to intravenous immunoglobulin (IVIg).

METHODS

Ten patients were selected with a slowly progressive, asymmetric, lower motor neuron disorder, and were treated prospectively with IVIg at a dose of 2g/kg over 5 days. All subjects had neurophysiological testing to look for evidence of conduction block before treatment. Muscle strength was assessed by MRC grades and hand held myometry, measuring pinch and grip strength. A 20% increase in both pinch and grip myometry was considered a positive response.

RESULTS

In no patient was conduction block detected. Four of the 10 patients showed a positive response to IVIg, with the best response occurring in two patients who presented with weakness but without severe muscle wasting. Three of the four responders have continued to receive IVIg for a mean period of 17 months (range 15-24 months), with continued effect. The response to IVIg was not related to the presence of anti-GM1 antiganglioside antibodies, but responders had a selective pattern of muscle weakness and normal (>90% predicted) vital capacity.

CONCLUSION

The findings suggest that a course of IVIg should be considered in patients with the clinical phenotype of multifocal motor neuropathy but without neurophysiological evidence of conduction block.

Schmidt-Lanterman's incisures--the principal target of autoimmune attack in demyelinating Guillain-Barré syndrome?

We used immunocytochemical staining of peripheral (trigeminal) nerve to screen sera of patients with Guillain-Barré syndrome (GBS) for the presence of autoantibodies, using sera from patients with other neurological diseases and healthy volunteers as controls. Most sera mildly reacted with axons, myelin sheaths, or sensory neurons without correlation to a specific disease. A characteristic staining, however, was found in 23 demyelinating cases (89%) out of 26 investigated GBS sera. With these sera, dark, oval and often paired small blobs were observed throughout the sections. A similar picture was rarely observed with sera from patients with other disorders or healthy controls. Using immunocytochemical marker proteins and high light microscopic resolution, the blobs were identified as Schmidt-Lanterman's incisures (SLIs). Further investigations will be necessary to identify the corresponding antigen and to answer the question, whether these antibodies represent an epiphenomenon or play a role in the causative mechanism of the disease.

The pattern of antiganglioside antibody reactivities producing myelinated nerve conduction block in vitro

We studied the pattern of human antiganglioside antibody reactivities causing an acute conduction block in rat myelinated nerve fibers, using an in vitro preparation of the sciatic-tibial nerve. With the aid of complements, IgM antibodies reacting with the terminal disaccharide of galactose (beta1-3)N-acetylgalactosamine produced the block. These findings may help us to understand the mechanism in which the conduction block occurs in neuropathies associated with antiganglioside antibodies.

Single fibre electromyography in multifocal motor neuropathy with persistent conduction blocks

OBJECTIVE

To study the process of denervation-reinnervation in multifocal motor neuropathy with persistent conduction blocks in clinically affected and unaffected muscles.

METHOD

Volitional single fibre electromyography (SFEMG) was performed in the extensor digitorum communis (EDC) of seven patients. The jitter, the fibre density, and the mean interpotential interval were determined. The results before and after treatment with intravenous immunoglobulin (IVIg) between the unaffected EDC and affected EDC examined during the same SFEMG session were also compared. In addition the values of jitter, fibre density, and mean interpotential interval were analysed for correlation with the strength score on the MRC scale, the duration of the neuropathy, the number of IVIg treatment periods, and the radial nerve conduction block values.

RESULTS

Mean jitter, percentage of jitters >60 micros, and impulse blocking percentage, were higher than normal in both the affected EDCs and to a lesser degree in unaffected EDCs. Jitter decreased significantly after IVIg and correlated only with the MRC score. Fibre density and mean interpotential interval were higher than normal equally in the affected EDC and unaffected EDCs, but no correlation was found with strength, duration of the neuropathy, number of treatment periods, and conduction block values.

CONCLUSION

The major finding is the presence of SFEMG abnormalities in clinically unaffected EDCs. This shows a process of denervation-reinnervation even in the absence of clinical symptoms, probably more frequent than commonly supposed in this neuropathy. The rapid clinical improvement after IVIg infusions could be due to remyelination after demyelination and to an interference of IVIg with the blocking effect of antibodies on the Na+ channels at the motor nerve endings.

The role of glycosphingolipids in neurological disorders. Mechanisms of immune action

Specific criteria that are required for understanding the significance of glycosphingolipid (GSL) antibodies, as well as mechanisms that may underlie the immunopathogenesis of these disorders, are proposed. These criteria are illustrated by describing the role of a unique family of acidic GSLs, the sulfated glucuronosyl glycolipids (SGGLs), in the pathogenic mechanisms of peripheral neuropathy with IgM paraproteinemia. High anti-SGGL antibody titers are detected in patients suffering from this disorder. It is demonstrated that SGGLs, which possess a common carbohydrate epitope with myelin-associated glycoprotein (MAG), several low-molecular-weight glycoproteins in the PNS, and a number of cell adhesion molecules, are potential target antigens for the neuropathy. Evidence is provided that sensitization of laboratory animals with pure SGGLs elicits experimental peripheral neuropathies that exhibit remarkable similarities with respect to antibody specificity, and electrophysiological and pathological features to the human conditions. By intraneural injection of antibodies into the sciatic nerve of rats, it is demonstrated that pathological changes consisting of demyelination and axonal degeneration are mediated by an antibody- and complement-dependent process. To elucidate the mechanisms of antibody penetration from circulation into the endoneurial space, it is further shown that brain microvascular endothelial cells express SGGLs. Moreover it has been found that inflammatory cytokines are capable of upregulating the expression of SGGLs on the endothelial cell surface, resulting in a greater attachment of leukocytes. This latter observation suggests that SGGLs may also participate in cell-mediated responses in certain inflammatory neurological disorders.

Association of IgM type anti-GM1 antibodies and muscle strength in chronic acquired demyelinating polyneuropathy

The pathogenetic role of anti-GM1 in chronic acquired demyelinating polyneuropathy (CADP) is uncertain. An association between antibodies and disease activity has not yet been established. In 8 patients with CADP followed longitudinally, anti-GM1 antibodies were monitored with a standardized enzyme-linked immunosorbent assay technique and muscle performance with isokinetic dynamometry. During a mean observation period of 24 months, strength improved in 6 of 8 patients by a median value of 54.5%, and anti-GM1 fell in all 6 patients; the reduction being 43%. In 2 patients, muscle performance deteriorated by 30 and 8%, whereas anti-GM1 titers increased by 10 and 9%, respectively. The relative change in anti-GM1 was inversely related to muscle performance. Clinical scoring of muscle performance according to the Medical Research Council scale failed to show an association with anti-GM1. It is concluded that anti-GM1 antibodies are closely related to disease activity, and that the close association indicates a role of anti-GM1 in the pathogenesis of CADP.

Antibody panels in idiopathic polyneuropathy and motor neuron disease

We prospectively evaluated patients with idiopathic polyneuropathy (PN) and motor neuron disease (MND) with commercial antibody (Ab) panels. Patients with sensorimotor PN received a "sensorimotor neuropathy profile" [3-sulfated glucuronyl paragloboside (SGPG)/myelin-associated glycoprotein (MAG), GM1, asialo-GM1, GD1b, Hu, sulfatide]. Motor neuropathy or MND patients underwent a "motor neuropathy profile" (SGPG/MAG, GM1, asialo-GM1). Seven of 78 patients (9.0%) with sensorimotor PN and 3 of 44 patients (6.8%) with MND had abnormal panels. None of 60 patients with axonal sensory or sensorimotor PN had antisulfatide Ab. Seven of 13 patients (54%) with multifocal motor neuropathy had abnormal panels, with 6 seropositive to GM1. We found abnormal Ab panels in fewer than 10% of patients with idiopathic sensorimotor PN and MND. Moreover, abnormal Ab tests often did not relate to the clinical context. Our data do not support the use of commercial Ab panels in the evaluation of patients with idiopathic PN or MND.

Glycosphingolipids as potential diagnostic markers and/or antigens in neurological disorders

Glycosphingolipids are most abundant in the nervous system within which are developmental, regional, structural and cellular differences regarding their composition. The are shedded to the cerebrospinal fluid and thus potential markers for pathogenic alterations in the brain, such as developmental abnormalities, demyelination, gliosis, neuronal cell destruction. The glycosphingolipids have also been found to be antigens in autoimmune processes involving the nervous system, in particular in peripheral neuropathies like Guillain Barré syndrome, multifocal motor neuropathy etc. The immune response might have been triggered by infectious agents with an antigen epitope which mimic the glycosphingolipid or by a primary nerve tissue damage leading to release of glycosphingolipids. There is a series of support for a clinical significance of cerebrospinal fluid glycosphingolipid determinations and the presence of anti-glycosphingolipid antibodies but this has to be further explored. This paper is a mini review of the state of the art and discuss methodological aspects and improvements that might help to explore the relevance of glycosphingolipids in neurological disorders.

Multifocal motor neuropathy: clinical and electrophysiological findings

Multifocal motor neuropathy (MMN) can be differentiated from motor neuron disease by electrophysiological evidence of conduction block. To increase the probability of recording conduction block, we studied the whole nerve length including proximal segments in 84 patients with pure motor syndromes, using a special stimulation technique. In 8 patients, the diagnosis of MMN was confirmed by electrophysiological evidence of conduction block or temporal dispersion. The typical clinical picture of MMN with chronic progressive, asymmetrical, marked distal weakness was observed in our patients. Electrophysiological routine tests of distal nerves were usually normal except in nerve segments with conduction block. In 4 patients, conduction block could be recorded only in proximal nerve segments or spinal roots. All patients showed rapid improvement of clinical features and parallel reduction of conduction block during or after high-dose intravenous immunoglobulin (ivIG) therapy, supporting the diagnosis of an immune-mediated neuropathy. Three of them are now in remission without any therapy, whereas 5 still receive a regular ivIG course every 2-12 weeks as long-term treatment. In all patients with pure or predominantly motor syndromes and normal findings in electrophysiological routine tests of distal nerve segments, there should be proximal conduction block studies to avoid overlooking a treatable disorder such as MMN.

Persistent increased threshold of electrical stimulation selective to motor nerve in multifocal motor neuropathy

In multifocal motor neuropathy (MMN) the threshold of electrical stimulation showed a persistent, marked increase for the motor nerve which decreased after treatment with intravenous immunoglobulin or oral cyclophosphamide; whereas, the threshold was normal for the sensory nerve. This discrepancy of the thresholds for motor and sensory nerves indicates that the increased threshold for motor nerve is not caused by change in perineural capacitance, such as subperi- and endoneural edema or perineural thickening. Inching studies showed that the site of the elevated motor nerve threshold was closely associated with conduction slowing and block. For the cause of the increased threshold, therefore, we suppose the presence of a factor which interferes with reorganization of the nodal property in the remyelinative process or which directly blocks sodium channels where the blood-nerve barrier is impaired in MMN.

AAEM case report #30: multifocal motor neuropathy

A 73-year-old man with a 16-year history of fasciculations and 15 years of weakness in his right arm was diagnosed with focal motor neuron disease. After 10 years of purely motor symptoms, he developed mild parasthesias although his sensory examination remained normal. Reflexes were reduced or absent in the weak muscles but were normal elsewhere. Nerve conduction was studied in nerves innervating weak muscles and showed severe motor conduction block. Sensory nerve conduction studies were minimally abnormal, showing reduced amplitudes with normal velocities. Based on the clinical picture and the presence of severe motor conduction block, the patient was diagnosed as multifocal motor neuropathy. Treatment with high-dose intravenous immunoglobulin was given with significant improvement in strength and partial resolution of the conduction block. As this case demonstrates, this treatable disorder may occasionally be mistaken for motor neuron disease although the resemblance is only superficial, and it should never be mistaken for amyotrophic lateral sclerosis. Multifocal motor neuropathy is an inflammatory, demyelinating neuropathy which, like chronic inflammatory demyelinating polyneuropathy (CIDP), is probably immune-mediated. It differs from typical CIDP by virtue of a marked predilection for motor axons, a strikingly restricted distribution, and a protracted course. Treatment with high-dose intravenous immunoglobulin is frequently helpful, but other forms of immune manipulation are less effective.

A somatically mutated human antiganglioside IgM antibody that induces experimental neuropathy in mice is encoded by the variable region heavy chain gene, V1-18

IgM paraproteins associated with autoimmune peripheral neuropathy and anti-Pr cold agglutinins react with sialic acid epitopes present on disialylated gangliosides including GD1b, GT1b, GQ1b, and GD3. A causal relationship between the paraprotein and the neuropathy has never been proven experimentally. From peripheral blood B cells of an affected patient, we have cloned a human hybridoma secreting an antidisialosyl IgM mAb, termed Ha1, that shows identical structural and functional characteristics to its serum counterpart. Variable region analysis shows Ha1 is encoded by the same VH1 family heavy chain gene, V1-18, as the only other known anti-Pr antibody sequence and is somatically mutated, suggesting that it [correction of is] arose in vivo in response to antigenic stimulation. In the rodent peripheral nervous system, Ha1 immunolocalizes to dorsal root ganglia, motor nerve terminals, muscle spindles, myelinated axons, and nodes of Ranvier. After intraperitoneal injection of affinity-purified antibody into mice for 10 d, electrophysiological recordings from the phrenic nerve-hemidiaphragm preparation demonstrated impairment of nerve excitability and a reduction in quantal release of neurotransmitter. These data unequivocally establish that an antidisialosyl antibody can exert pathophysiological effects on the peripheral nervous system and strongly support the view that the antibody contributes to the associated human disease.

Multifocal motor neuropathy human sera block distal motor nerve conduction in mice

Multifocal motor neuropathy (MMN) is associated with serum autoantibodies to gangliosides, but their pathogenic role is uncertain. We have used a novel approach to study the effects of serum and plasma from 8 patients with this syndrome, 6 of whom were anti-GM1 positive. The nerve stimulus required to evoke muscle contraction and endplate potentials (EPPs) was measured in the mouse phrenic nerve-diaphragm preparation during 4 to 6 hours of direct application (plasma at 1:1 or serum 1:2 dilution) and following intraperitoneal injection of plasma (1 ml/day) for 1 to 5 days ("passive transfer"). Direct application of MMN serum or plasma produced a progressive increase in stimulus threshold, followed by complete block of nerve-evoked muscle contraction in 3 cases, and an associated decline to about 50% of the EPP amplitude followed by sudden loss of EPPs. These effects were complement independent. Even with complete block of nerve-evoked EPPs, miniature EPP (MEPP) frequency could be increased by raising external K+ to depolarize the nerve terminal directly. Passive transfer of 1 ml of MMN plasma (n = 5) for 3 days caused similar but less marked changes. These results demonstrate that serum factors in MMN can block nerve conduction at distal motor nerves.

Neuromuscular disease: rehabilitation and electrodiagnosis. 2. Nerve disease

The purpose of this section of the Self-Directed Physiatric Education Program Study Guide on rehabilitation in diseases affecting nerve and muscle is to assist practitioners and trainees in physical medicine and rehabilitation by providing an overview of the evaluation, treatment, and rehabilitative care of patients with inherited and acquired neuropathies. Both diffuse and focal processes are discussed. Current research is briefly reviewed, and the utility and limitations of electrodiagnostic studies are discussed.

Antiglycolipid antibodies in peripheral neuropathy: fact or fiction?

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Anti-GM1 antibodies in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) treated with intravenous immunoglobulin (IVIg)

Patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and with a chronic polyneuropathy (non-CIDP) were studied for the presence of anti-GM1 antibodies. In pretreatment sera of CIDP patients, we found IgG anti-GM1 antibodies in 23%, IgM in 7%, and IgA in 14%. Predominantly motor involvement was associated with IgG and IgM anti-GM1 antibodies in CIDP patients (P = 0.002). Improvement after intravenous immunoglobulin (IVIg) therapy was not associated with anti-GM1 antibody titer before or after treatment. Anti-GM1 antibody titers before onset of treatment was not related to poor clinical outcome, although large clinical improvements after IVIg therapy were observed less often (P = 0.057) in patients with high titer anti-GM1 antibodies before treatment.