Demyelination induced by intraneural injection of human antimyelin-associated glycoprotein antibodies

Anti-MAG neuropathy: historical aspects, clinical-pathological correlations, and considerations for future therapeutical trials

BACKGROUND

 Patients with anti-MAG neuropathy present with distal demyelinating polyneuropathy, IgM monoclonal gammopathy, and elevated titers of anti-MAG antibodies.

OBJECTIVE

 This paper reviews what is known about the clinical presentation, course, pathophysiology, and treatment of anti-MAG neuropathy, with considerations for the design of therapeutic trials.

METHODS

 A literature review of the medical and scientific literature related to anti-MAG neuropathy, and the design of therapeutic clinical trials in peripheral neuropathy.

RESULTS

 Anti-MAG neuropathy can remain indolent for many years but then enter a progressive phase. Highly elevated antibody titers are diagnostic, but intermediate titers can also occur in chronic inflammatory demyelinating polyneuropathy (CIDP). The peripheral nerves can become inexcitable, thereby masking the demyelinating abnormalities. There is good evidence that the anti-MAG antibodies cause neuropathy. Reduction of the autoantibody concentration by agents that target B-cells was reported to result in clinical improvement in case series and uncontrolled trials, but not in controlled clinical trials, probably due to inadequate trial design.

CONCLUSION

 We propose that therapeutic trials for anti-MAG neuropathy include patients with the typical presentation, some degree of weakness, highly elevated anti-MAG antibody titers, and at least one nerve exhibiting demyelinating range abnormalities. Treatment with one or a combination of anti-B-cell agents would aim at reducing the autoantibody concentration by at least 60%. A trial duration of 2 years may be required to show efficacy. The neuropathy impairment score of the lower extremities (NIS-LL) plus the Lower Limb Function (LLF) score would be a suitable primary outcome measure.

Anti-myelin-associated glycoprotein neuropathy: Where do we stand?

Myelin-associated glycoprotein (MAG) is a transmembrane glycoprotein concentrated in periaxonal Schwann cell and oligodendroglial membranes of myelin sheaths that serves as an antigen for immunoglobulin M (IgM) monoclonal antibodies. Individuals who harbor anti-MAG antibodies classically develop a progressive autoimmune peripheral neuropathy characterized clinically by ataxia, distal sensory loss, and gait instability, and electrophysiologically by distally accentuated conduction velocity slowing. Although off-label immunotherapy is common, there are currently no proven effective disease-modifying therapeutics, and most patients experience slow accumulation of disability over years and decades. The typically slowly progressive nature of this neuropathy presents unique challenges when trying to find effective anti-MAG therapeutic agents. Drug development has also been hampered by the lack of validated outcome measures that can detect clinically meaningful changes in a reasonable amount of time as well as by the lack of disease activity biomarkers. In this invited review, we provide an update on the state of clinicometric outcome measures and disease activity biomarkers in anti-MAG neuropathy. We highlight the insensitivity of widely used existing clinicometric outcome measures such as the Inflammatory Neuropathy Cause and Treatment (INCAT) disability score as well as the INCAT sensory subscore in anti-MAG neuropathy, referencing the two previous negative randomized controlled clinical trials evaluating rituximab. We then discuss newly emerging candidate therapeutic agents, including tyrosine kinase inhibitors and enhanced B-cell-depleting agents, among others. We conclude with a practical approach to the evaluation and management of anti-MAG neuropathy patients.

Autocrine TNF-α Increases Penetration of Myelin-Associated Glycoprotein Antibodies Across the Blood-Nerve Barrier in Anti-MAG Neuropathy

BACKGROUND AND OBJECTIVES

Deposition of myelin-associated glycoprotein (MAG) immunoglobulin M (IgM) antibodies in the sural nerve is a key feature in anti-MAG neuropathy. Whether the blood-nerve barrier (BNB) is disrupted in anti-MAG neuropathy remains elusive.We aimed to evaluate the effect of sera from anti-MAG neuropathy at the molecular level using our in vitro human BNB model and observe the change of BNB endothelial cells in the sural nerve of anti-MAG neuropathy.

METHODS

Diluted sera from patients with anti-MAG neuropathy (n = 16), monoclonal gammopathies of undetermined significance (MGUS) neuropathy (n = 7), amyotrophic lateral sclerosis (ALS, n = 10), and healthy controls (HCs, n = 10) incubated with human BNB endothelial cells to identify the key molecule of BNB activation using RNA-seq and a high-content imaging system, and exposed with a BNB coculture model to evaluate small molecule/IgG/IgM/anti-MAG antibody permeability.

RESULTS

RNA-seq and the high-content imaging system showed the significant upregulation of tumor necrosis factor (TNF-α) and nuclear factor-kappa B (NF-κB) in BNB endothelial cells after exposure to sera from patients with anti-MAG neuropathy, whereas the serum TNF-α concentration was not changed among the MAG/MGUS/ALS/HC groups. Sera from patients with anti-MAG neuropathy did not increase 10-kDa dextran or IgG permeability but enhanced IgM and anti-MAG antibody permeability. Sural nerve biopsy specimens from patients with anti-MAG neuropathy showed higher TNF-α expression levels in BNB endothelial cells and preservation of the structural integrity of the tight junctions and the presence of more vesicles in BNB endothelial cells. Neutralization of TNF-α reduces IgM/anti-MAG antibody permeability.

DISCUSSION

Sera from individuals with anti-MAG neuropathy increased transcellular IgM/anti-MAG antibody permeability via autocrine TNF-α secretion and NF-κB signaling in the BNB.

Polyneuropathy Associated with IgM Monoclonal Gammopathy; Advances in Genetics and Treatment, Focusing on Anti-MAG Antibodies

With increasing age, the chances of developing either MGUS or polyneuropathy increase as well. In some cases, there is a causative relationship between the IgM M-protein and polyneuropathy. In approximately half of these cases, IgM targets the myelin-associated glycoprotein (MAG). This results in chronic polyneuropathy with slowly progressive, predominantly sensory neurological deficits and distally demyelinating features in nerve conduction studies. Despite the disease being chronic and developing slowly, it can cause considerable impairment. We reviewed English medical publications between 1980 and May 2022 on IgM gammopathy-associated polyneuropathy, with special attention to studies addressing the pathophysiology or treatment of anti-MAG polyneuropathy. Treatment options have been limited to a temporizing effect of intravenous immunoglobulins in some patients and a more sustained effect of rituximab but in only 30 to 55 percent of patients. An increase in our knowledge concerning genetic mutations, particularly the MYD88L265P mutation, led to the development of novel targeted treatment options such as BTK inhibitors. Similarly, due to the increasing knowledge of the pathophysiology of anti-MAG polyneuropathy, new treatment options are emerging. Since anti-MAG polyneuropathy is a rare disease with diverse symptomatology, large trials with good outcome measures are a challenge.

Anti-MAG neuropathy: From biology to clinical management

The acquired chronic demyelinating neuropathies include a growing number of disease entities that have characteristic, often overlapping, clinical presentations, mediated by distinct immune mechanisms, and responding to different therapies. After the discovery in the early 1980s, that the myelin associated glycoprotein (MAG) is a target antigen in an autoimmune demyelinating neuropathy, assays to measure the presence of anti-MAG antibodies were used as the basis to diagnose the anti-MAG neuropathy. The route was open for describing the clinical characteristics of this new entity as a chronic distal large fiber sensorimotor neuropathy, for studying its pathogenesis and devising specific treatment strategies. The initial use of chemotherapeutic agents was replaced by the introduction in the late 1990s of rituximab, a monoclonal antibody against CD20⁺ B-cells. Since then, other anti-B cells agents have been introduced. Recently a novel antigen-specific immunotherapy neutralizing the anti-MAG antibodies with a carbohydrate-based ligand mimicking the natural HNK-1 glycoepitope has been described.

Immune mechanisms, the role of complement, and related therapies in autoimmune neuropathies

INTRODUCTION

Autoimmune neuropathies have diverse presentations and underlying immune mechanisms. Demonstration of efficacy of therapeutic agents that inhibit the complement cascade would confirm the role of complement activation.

AREAS COVERED

A review of the pathophysiology of the autoimmune neuropathies, to identify those that are likely to be complement mediated.

EXPERT OPINION

Complement mediated mechanisms are implicated in the acute and chronic neuropathies associated with IgG or IgM antibodies that target the Myelin Associated Glycoprotein (MAG) or gangliosides in the peripheral nerves. Antibody and complement mechanisms are also suspected in the Guillain-Barré syndrome and chronic inflammatory demyelinating neuropathy, given the therapeutic response to plasmapheresis or intravenous immunoglobulins, even in the absence of an identifiable target antigen. Complement is unlikely to play a role in paraneoplastic sensory neuropathy associated with antibodies to HU/ANNA-1 given its intracellular localization. In chronic demyelinating neuropathy with anti-nodal/paranodal CNTN1, NFS-155, and CASPR1 antibodies, myotonia with anti-VGKC LGI1 or CASPR2 antibodies, or autoimmune autonomic neuropathy with anti-gAChR antibodies, the response to complement inhibitory agents would depend on the extent to which the antibodies exert their effects through complement dependent or independent mechanisms. Complement is also likely to play a role in Sjogren's, vasculitic, and cryoglobulinemic neuropathies.

Antibody testing in neuropathy associated with anti-Myelin-Associated Glycoprotein antibodies: where we are after 40 years

PURPOSE OF REVIEW

The diagnosis of Myelin-Associated Glycoprotein (MAG) neuropathy is based on the presence of elevated titers of IgM anti-MAG antibodies, which are typically associated with IgM monoclonal gammopathy, and a slowly progressive, distal demyelinating phenotype. The condition, however, can be under or over diagnosed in patients with mildly elevated antibody titers, absent monoclonal gammopathy, or an atypical presentation. The purpose of this paper is to examine recent advances in our understanding of the currently available anti-MAG antibody assays, their reliability, and their use in deciding treatment or monitoring the response to therapy.

RECENT FINDINGS

Higher titers of anti-MAG antibodies are more likely to be associated with the typical MAG phenotype or response to therapy. Mildly elevated antibody levels can occur in patients with chronic inflammatory demyelinating polyneuropathy. Testing for cross-reactivity with HNK1 can add to the specificity of the antibody assays. Patients with MAG neuropathy can present with an atypical phenotype and in the absence of a detectable monoclonal gammopathy.

SUMMARY

Assays for anti-MAG antibodies by Enzyme-Linked Immunosorbent Assay can be improved by testing for antibody binding at multiple serum dilutions, the inclusion of antigen-negative microwells as internal controls for each sample, testing for cross-reactivity with HNK1, and formal validation. The diagnosis needs to be considered in patients with demyelinating neuropathy, even in the absence of a monoclonal gammopathy or typical phenotype. The change in antibody levels needs to be considered in evaluating the response to therapy with B-cell depleting agents.

Mechanisms of Nerve Damage in Neuropathies Associated with Hematological Diseases: Lesson from Nerve Biopsies

Despite the introduction of non-invasive techniques in the study of peripheral neuropathies, sural nerve biopsy remains the gold standard for the diagnosis of several neuropathies, including vasculitic neuropathy and neurolymphomatosis. Besides its diagnostic role, sural nerve biopsy has helped to shed light on the pathogenic mechanisms of different neuropathies. In the present review, we discuss how pathological findings helped understand the mechanisms of polyneuropathies complicating hematological diseases.

Selective inhibition of anti-MAG IgM autoantibody binding to myelin by an antigen-specific glycopolymer

Anti‐myelin‐associated glycoprotein (MAG) neuropathy is a disabling autoimmune peripheral neuropathy that is caused by circulating monoclonal IgM autoantibodies directed against the human natural killer‐1 (HNK‐1) epitope. This carbohydrate epitope is highly expressed on adhesion molecules such as MAG, a glycoprotein present in myelinated nerves. We previously showed the therapeutic potential of the glycopolymer poly(phenyl disodium 3‐O‐sulfo‐β‐d‐glucopyranuronate)‐(1→3)‐β‐d‐galactopyranoside (PPSGG) in selectively neutralizing anti‐MAG IgM antibodies in an immunological mouse model and ex vivo with sera from anti‐MAG neuropathy patients. PPSGG is composed of a biodegradable backbone that multivalently presents a mimetic of the HNK‐1 epitope. In this study, we further explored the pharmacodynamic properties of the glycopolymer and its ability to inhibit the binding of anti‐MAG IgM to peripheral nerves. The polymer selectively bound anti‐MAG IgM autoantibodies and prevented the binding of patients’ anti‐MAG IgM antibodies to myelin of non‐human primate sciatic nerves. Upon PPSGG treatment, neither activation nor inhibition of human and murine peripheral blood mononuclear cells nor alteration of systemic inflammatory markers was observed in mice or ex vivo in human peripheral blood mononuclear cells. Intravenous injections of PPSGG to mice immunized against the HNK‐1 epitope removed anti‐MAG IgM antibodies within less than 1 hr, indicating a fast and efficient mechanism of action as compared to a B‐cell depletion with anti‐CD20. In conclusion, these observations corroborate the therapeutic potential of PPSGG for an antigen‐specific treatment of anti‐MAG neuropathy.

Read the Editorial Highlight for this article on page 465.

Native versus deglycosylated IgM in anti-MAG neuropathy: Correlation with clinical status - Study of 10 cases

BACKGROUND/PURPOSE

In anti-myelin associated glycoprotein (anti-MAG) neuropathies, there is evidence that anti-MAG antibodies are pathogenic but numerous studies report the absence or a weak correlation between the titers of these antibodies and disease course. In this study we assessed the relationships between MAG and glycosylated moieties located on Fc fragment of IgM anti-MAG.

MATERIAL AND METHODS

IgM were extracted from the serum of 8 patients with anti-MAG neuropathy and in 2 patients with anti-MAG antibodies without anti-MAG neuropathy. Anti-MAG activity was performed with pre- and post-deglycosylated IgM extracts using indirect immunofluorescence (IIF) and ELISA. Sera from 49 patients with IgM monoclonal gammopathy without neurological disease were tested as control group (CG). Results were compared to clinical scores. For 4 patients the affinity constant of IgM with MAG was analyzed pre- and post-deglycosylated, using surface plasmon resonance technology (SPR).

RESULTS

The relationships between MAG and glycosylated moieties of IgM anti-MAG were confirmed by kinetic and immunological assays. Deglycosylation resulted in a decrease in anti-MAG titers. Post-deglycosylation anti-MAG titers trended with changes in IgM titers and allowed quantifying anti-MAG antibodies without a saturation of the testing method. After deglycosylation, the titers better represented pathogenic activity and help to follow a given patient's clinical status prospectively. Six patients from CG (12.2%) had anti-MAG antibody titers over positive threshold: 1000 Bühlmann-Titer-Units (BTU) supporting the hypothesis of neutral intermolecular interactions between IgM and MAG. Deglycosylation allowed distinguishing infra clinical forms from neutral relationships forms, when the titers are weak but this assay remains essentially a diagnostic tool.

Neuropathy associated with immunoglobulin M monoclonal gammopathy: A combined sonographic and nerve conduction study

Introduction

We assessed the specific sonographic pattern of structural nerve abnormalities in immunoglobulin M (IgM) neuropathy and disease controls.

Methods

We enrolled 106 incident patients—32 patients with IgM neuropathy, 42 treatment‐naive patients with chronic inflammatory demyelinating polyneuropathy, and 32 patients with axonal neuropathies. All patients underwent standardized ancillary testing in addition to standardized sonography of the brachial plexus and the large arm and leg nerves bilaterally.

Results

We found widespread nerve enlargement in IgM neuropathy and chronic inflammatory demyelinating polyneuropathy (CIDP), with specific enlargement of brachial plexus and proximal segments of median nerve but not in axonal disease controls (P < .001). Sonographic nerve hypertrophy in IgM neuropathy was not associated with nerve conduction, clinical, or laboratory characteristics.

Discussion

Immunoglobulin M neuropathy is characterized by widespread nerve enlargement indistinguishable from CIDP. Our data provide evidence to confirm that the disease process is not confined to the more distal parts of nerves in either classical demyelinating or axonal variants of neuropathy with associated IgM.

Anti-ganglioside Antibodies in Peripheral Nerve Pathology

Anti-ganglioside antibodies are principally associated with autoimmune peripheral neuropathies. In these disorders, immune attack is inadvertently directed at peripheral nerve by autoantibodies that target glycan structures borne by glycolipids, particularly gangliosides concentrated in nerve myelin and axons. The most thoroughly studied disorder is the acute paralytic disease, Guillain-Barré syndrome (GBS) in which IgG autoantibodies against gangliosides arise following acute infections, notably Campylobacter jejuni enteritis. Additionally, chronic autoimmune neuropathies are associated with IgM antibodies directed against many glycolipids including gangliosides. This introductory chapter briefly summarizes the immunological and pathological features of these disorders, focusing on the methodological development of antibody measurement and of animal models.

Anti-MAG neuropathy: Role of IgM antibodies, the paranodal junction and juxtaparanodal potassium channels

OBJECTIVE

To improve understanding of disease pathophysiology in anti-myelin-associated glycoprotein (anti-MAG) neuropathy to guide further treatment approaches.

METHODS

Anti-MAG neuropathy patients underwent clinical assessments, nerve conduction and excitability studies, and ultrasound assessment.

RESULTS

Patients demonstrated a distinctive axonal excitability profile characterised by a reduction in superexcitability [MAG: -14.2 ± 1.6% vs healthy controls (HC): -21.8 ± 1.2%; p < 0.01] without alterations in most other excitability parameters. Mathematical modelling of nerve excitability recordings suggested that changes in axonal function could be explained by a 72.5% increase in juxtaparanodal fast potassium channel activation and an accompanying hyperpolarization of resting membrane potential (by 0.3 mV) resulting in a 94.2% reduction in discrepancy between anti-MAG data and the healthy control model. Superexcitability changes correlated strongly with clinical and neurophysiological parameters. Furthermore, structural assessments demonstrated a proximal pattern of nerve enlargement (C6 nerve root cross-sectional area: 15.9 ± 8.1 mm² vs HC: 9.1 ± 2.3 mm²; p < 0.05).

CONCLUSIONS

The imaging and neurophysiological results support the pathogenicity of anti-MAG IgM. Widening between adjacent loops of paranodal myelin due to antibodies would expand the pathway from the node to the juxtaparanode, increasing activation of juxtaparanodal fast potassium channels, thereby impairing saltatory conduction.

SIGNIFICANCE

Potassium channel blockers may prove beneficial in restoring conduction closer to its normal state and improving nerve function in anti-MAG neuropathy.

Advances in the diagnosis, immunopathogenesis and therapies of IgM-anti-MAG antibody-mediated neuropathies

Polyneuropathy with immunoglobulin M (IgM) monoclonal gammopathy is the most common paraproteinemic neuropathy, comprising a clinicopathologically and immunologically distinct entity. The clinical spectrum spans from distal paresthesias and mild gait imbalance to more severe sensory ataxia, with falls and a varying degree of distal sensorimotor deficits. In approximately 75% of patients, the monoclonal IgM immunoreacts with myelin-associated glycoprotein (MAG) and sulfoglucuronyl glycosphingolipid (SGPG), or other peripheral nerve glycolipids that serve as antigens. These antibodies are considered pathogenic because IgM and complement are deposited on the myelin sheath, splitting the myelin lamellae, while adoptive transfer of patients’ IgM into susceptible host animals causes sensory ataxia and reproduces the human pathology. In spite of the apparently convincing pathogenicity of these antibodies, the response to immunotherapies remains suboptimal. Clorambuscil, cladibrine, cyclophospamide and intravenous immunoglobulin may help some patients but the benefits are minimal and transient. Open-label studies in >200 patients indicate that rituximab is helpful in 30–50% of these patients, even with long-term benefits, probably by suppressing IgM anti-MAG antibodies or inducing immunoregulatory T cells. Two controlled studies with rituximab did not however meet the primary endpoint, mostly because of the poor sensitivity of the scales used; they did however show statistical improvement in secondary endpoints and improved clinical functions in several patients. This review provides an overview of the clinical phenotypes and immunoreactivity of IgM to glycolipids or glycoproteins of peripheral nerve myelin, summarizes the progress on treatment with rituximab as a promising therapy, discusses the pitfalls of scales used, identifies possible biomarkers of response to therapy and highlights the promising new anti-B cell or target-specific immunotherapies.

Autoantibodies in chronic inflammatory neuropathies: diagnostic and therapeutic implications

The chronic inflammatory neuropathies (CINs) are rare, very disabling autoimmune disorders that generally respond well to immune therapies such as intravenous immunoglobulin (IVIg). The most common forms of CIN are chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), multifocal motor neuropathy, and polyneuropathy associated with monoclonal gammopathy of unknown significance. The field of CIN has undergone a major advance with the identification of IgG4 autoantibodies directed against paranodal proteins in patients with CIDP. Although these autoantibodies are only found in a small subset of patients with CIDP, they can be used to guide therapeutic decision-making, as these patients have a poor response to IVIg. These observations provide proof of concept that identifying the target antigens in tissue-specific antibody-mediated autoimmune diseases is important, not only to understand their underlying pathogenic mechanisms, but also to correctly diagnose and treat affected patients. This state-of-the-art Review focuses on the role of autoantibodies against nodes of Ranvier in CIDP, a clinically relevant emerging field of research. The role of autoantibodies in other immune-mediated neuropathies, including other forms of CIN, primary autoimmune neuropathies, neoplasms, and systemic diseases that resemble CIN, are also discussed.

Selective in vivo removal of pathogenic anti-MAG autoantibodies, an antigen-specific treatment option for anti-MAG neuropathy

Anti-MAG (myelin-associated glycoprotein) neuropathy is a disabling autoimmune peripheral neuropathy caused by monoclonal IgM autoantibodies that recognize the carbohydrate epitope HNK-1 (human natural killer-1). This glycoepitope is highly expressed on adhesion molecules, such as MAG, present in myelinated nerve fibers. Because the pathogenicity and demyelinating properties of anti-MAG autoantibodies are well established, current treatments are aimed at reducing autoantibody levels. However, current therapies are primarily immunosuppressive and lack selectivity and efficacy. We therefore hypothesized that a significant improvement in the disease condition could be achieved by selectively neutralizing the pathogenic anti-MAG antibodies with carbohydrate-based ligands mimicking the natural HNK-1 glycoepitope 1. In an inhibition assay, a mimetic (2, mimHNK-1) of the natural HNK-1 epitope blocked the interaction of MAG with pathogenic IgM antibodies from patient sera but with only micromolar affinity. Therefore, considering the multivalent nature of the MAG-IgM interaction, polylysine polymers of different sizes were substituted with mimetic 2. With the most promising polylysine glycopolymer PL₈₄(mimHNK-1)₄₅ the inhibitory effect on patient sera could be improved by a factor of up to 230,000 per epitope, consequently leading to a low-nanomolar inhibitory potency. Because clinical studies indicate a correlation between the reduction of anti-MAG IgM levels and clinical improvement, an immunological surrogate mouse model for anti-MAG neuropathy producing high levels of anti-MAG IgM was developed. The observed efficient removal of these antibodies with the glycopolymer PL₈₄(mimHNK-1)₄₅ represents an important step toward an antigen-specific therapy for anti-MAG neuropathy.

Immunotherapy for IgM anti-myelin-associated glycoprotein paraprotein-associated peripheral neuropathies

BACKGROUND

Serum monoclonal anti-myelin-associated glycoprotein (anti-MAG) antibodies may be pathogenic in some people with immunoglobulin M (IgM) paraprotein and demyelinating neuropathy. Immunotherapies aimed at reducing the level of these antibodies might be expected to be beneficial. This is an update of a review first published in 2003 and previously updated in 2006 and 2012.

OBJECTIVES

To assess the effects of immunotherapy for IgM anti-MAG paraprotein-associated demyelinating peripheral neuropathy.

SEARCH METHODS

On 1 February 2016 we searched the Cochrane Neuromuscular Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and Embase for randomised controlled trials (RCTs). We also checked trials registers and bibliographies, and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) or quasi-RCTs involving participants of any age treated with any type of immunotherapy for anti-MAG antibody-associated demyelinating peripheral neuropathy with monoclonal gammopathy of undetermined significance and of any severity.Our primary outcome measures were numbers of participants improved in disability assessed with either or both of the Neuropathy Impairment Scale (NIS) or the modified Rankin Scale (mRS) at six months after randomisation. Secondary outcome measures were: mean improvement in disability, assessed with either the NIS or the mRS, 12 months after randomisation; change in impairment as measured by improvement in the 10-metre walk time, change in a validated linear disability measure such as the Rasch-built Overall Disability Scale (R-ODS) at six and 12 months after randomisation, change in subjective clinical scores and electrophysiological parameters at six and 12 months after randomisation; change in serum IgM paraprotein concentration or anti-MAG antibody titre at six months after randomisation; and adverse effects of treatments.

DATA COLLECTION AND ANALYSIS

We followed standard methodological procedures expected by Cochrane.

MAIN RESULTS

We identified eight eligible trials (236 participants), which tested intravenous immunoglobulin (IVIg), interferon alfa-2a, plasma exchange, cyclophosphamide and steroids, and rituximab. Two trials of IVIg (22 and 11 participants, including 20 with antibodies against MAG), had comparable interventions and outcomes, but both were short-term trials. We also included two trials of rituximab with comparable interventions and outcomes.There were very few clinical or statistically significant benefits of the treatments used on the outcomes predefined for this review, but not all the predefined outcomes were used in every included trial and more responsive outcomes are being developed. A well-performed trial of IVIg, which was at low risk of bias, showed a statistical benefit in terms of improvement in mRS at two weeks and 10-metre walk time at four weeks, but these short-term outcomes are of questionable clinical significance. Cyclophosphamide failed to show any benefit in the single trial's primary outcome, and showed a barely significant benefit in the primary outcome specified here, but some toxic adverse events were identified.Two trials of rituximab (80 participants) have been published, one of which (26 participants) was at high risk of bias. In the meta-analysis, although the data are of low quality, rituximab is beneficial in improving disability scales (Inflammatory Neuropathy Cause and Treatment (INCAT) improved at eight to 12 months (risk ratio (RR) 3.51, 95% confidence interval (CI) 1.30 to 9.45; 73 participants)) and significantly more participants improve in the global impression of change score (RR 1.86, 95% CI 1.27 to 2.71; 70 participants). Other measures did not improve significantly, but wide CIs do not preclude some effect. Reported adverse effects of rituximab were few, and mostly minor.There were few serious adverse events in the other trials.

AUTHORS' CONCLUSIONS

There is inadequate reliable evidence from trials of immunotherapies in anti-MAG paraproteinaemic neuropathy to form an evidence base supporting any particular immunotherapy treatment. IVIg has a statistically but probably not clinically significant benefit in the short term. The meta-analysis of two trials of rituximab provides, however, low-quality evidence of a benefit from this agent. The conclusions of this meta-analysis await confirmation, as one of the two included studies is of very low quality. We require large well-designed randomised trials of at least 12 months' duration to assess existing or novel therapies, preferably employing unified, consistent, well-designed, responsive, and valid outcome measures.

The Spectrum and Pathogenesis of Antibody-mediated Neuropathies

Antibodies reacting with carbohydrate epitopes on neural glycoconjugates are present in several forms of neuropathy. These include monoclonal antibodies to the myelin-associated glycoprotein (MAG) and to gan gliosides in patients with neuropathy in association with IgM gammopathy, as well as polyclonal antibodies to gangliosides in inflammatory polyneuropathies, such as Guillain-Barré syndrome and multifocal motor neuropathy. There are several correlations between antibody specificity and clinical symptoms, including anti-MAG antibodies with demyelinating sensory or sensorimotor neuropathy, anti-GM1 ganglioside anti bodies with motor nerve disorders, anti-GQ1b ganglioside antibodies with Miller-Fisher syndrome, and antibodies to gangliosides containing disialosyl moieties with sensory ataxic neuropathy. This review will emphasize recent developments concerning the origins of the anti-glycoconjugate antibodies in patients, pathogenic mechanisms by which the antibodies may cause the neuropathies, and the implications of these findings for therapy. NEUROSCIENTIST 3:195-204, 1997

Diagnosis and treatment of chronic acquired demyelinating polyneuropathies

Chronic neuropathies are operationally classified as primarily demyelinating or axonal, on the basis of electrodiagnostic or pathological criteria. Demyelinating neuropathies are further classified as hereditary or acquired-this distinction is important, because the acquired neuropathies are immune-mediated and, thus, amenable to treatment. The acquired chronic demyelinating neuropathies include chronic inflammatory demyelinating polyneuropathy (CIDP), neuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG; anti-MAG neuropathy), multifocal motor neuropathy (MMN), and POEMS syndrome. They have characteristic--though overlapping--clinical presentations, are mediated by distinct immune mechanisms, and respond to different therapies. CIDP is the default diagnosis if the neuropathy is demyelinating and no other cause is found. Anti-MAG neuropathy is diagnosed on the basis of the presence of anti-MAG antibodies, MMN is characterized by multifocal weakness and motor conduction blocks, and POEMS syndrome is associated with IgG or IgA λ-type monoclonal gammopathy and osteosclerotic myeloma. The correct diagnosis, however, can be difficult to make in patients with atypical or overlapping presentations, or nondefinitive laboratory studies. First-line treatments include intravenous immunoglobulin (IVIg), corticosteroids or plasmapheresis for CIDP; IVIg for MMN; rituximab for anti-MAG neuropathy; and irradiation or chemotherapy for POEMS syndrome. A correct diagnosis is required for choosing the appropriate treatment, with the aim of preventing progressive neuropathy.

Neuropathy and monoclonal gammopathy

The association of neuropathy with monoclonal gammopathy has been known for several years, even if the clinical and pathogenetic relevance of this association is not completely defined. This is not a marginal problem since monoclonal gammopathy is present in 1-3% of the population above 50 years in whom it is often asymptomatic, and in at least 8% of patients is associated with a symptomatic neuropathy, representing one of the leading causes of neuropathy in aged people. Monoclonal gammopathy may result from malignant lymphoproliferative diseases including multiple myeloma or solitary plasmocytoma, Waldenström's macroglobulinemia (WM), other IgM-secreting lymphoma or chronic lymphocytic leukemia, and primary systemic amyloidosis (AL). In most instances it is not associated with any of these disorders and is defined monoclonal gammopathy of undetermined significance (MGUS) for its possible, though infrequent, evolution into malignant forms. Several data support the pathogenetic role of the monoclonal gammopathy in the neuropathy particularly when of IgM isotype where IgM reactivity to several neural antigens has been reported. Increased levels of VEGF have been implicated in POEMS syndrome. However, there are as yet no defined therapies for these neuropathies, as their efficacy has not been confirmed in randomized trials.

Immunotherapy for IgM anti-myelin-associated glycoprotein paraprotein-associated peripheral neuropathies

BACKGROUND

Serum monoclonal anti-myelin-associated glycoprotein antibodies may be pathogenic in some people with immunoglobulin M (IgM) paraprotein and demyelinating neuropathy. Immunotherapies aimed at reducing the level of these antibodies might be expected to be beneficial. This is an update of a review first published in 2003 and previously updated in 2006.

OBJECTIVES

To assess the effects of immunotherapy for IgM anti-myelin-associated glycoprotein paraprotein-associated demyelinating peripheral neuropathy.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register 6 June 2011), CENTRAL (2011, Issue 2), MEDLINE (January 1966 to May 2011) and EMBASE (January 1980 to May 2011) for controlled trials. We also checked bibliographies and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomised or quasi-randomised controlled trials involving participants of any age treated with any type of immunotherapy for anti-myelin-associated glycoprotein antibody-associated demyelinating peripheral neuropathy with monoclonal gammopathy of undetermined significance and of any severity.Our primary outcome measure was change in the Neuropathy Impairment Scale or Modified Rankin Scale at six months after randomisation. Secondary outcome measures were: Neuropathy Impairment Scale or the Modified Rankin Score at 12 months after randomisation; 10-metre walk time, subjective clinical scores and electrophysiological parameters at six and 12 months after randomisation; IgM paraprotein levels and anti-myelin-associated glycoprotein antibody titres at six months after randomisation; and adverse effects of treatments.

DATA COLLECTION AND ANALYSIS

The two authors independently selected studies. Two authors independently assessed the risk of bias in included studies.

MAIN RESULTS

We identified seven eligible trials (182 participants), which tested intravenous immunoglobulin, alfa interferon alfa-2a, plasma exchange, cyclophosphamide and steroids, and rituximab. Only two trials, of intravenous immunoglobulin (with 33 participants, including 20 with antibodies against myelin-associated glycoprotein), had comparable interventions and outcomes, but both were short-term trials.There were no clinical or statistically significant benefits of the treatments used on the outcomes predefined for this review, but not all the predefined outcomes were used in every included trial. Intravenous immunoglobulin showed a statistical benefit in terms of improvement in Modified Rankin Scale at two weeks and 10-metre walk time at four weeks. Cyclophosphamide failed to show any benefit in the trial's primary outcome, and showed a barely significant benefit in the primary outcome specified here, but some toxic adverse events were identified. A trial of rituximab was of poor methodological quality with a high risk of bias and a further larger study is awaited. Serious adverse events were few in the other trials.

AUTHORS' CONCLUSIONS

There is inadequate reliable evidence from trials of immunotherapies in anti-myelin-associated glycoprotein paraproteinaemic neuropathy to form an evidence base supporting any particular immunotherapy treatment. There is very low quality evidence of benefit from rituximab. Large well designed randomised trials of at least six to 12 months duration are required to assess existing or novel therapies, preferably employing unified, consistent, well designed, responsive and valid outcome measures.

Rituximab induces sustained reduction of pathogenic B cells in patients with peripheral nervous system autoimmunity

The B cell-depleting IgG1 monoclonal antibody rituximab can persistently suppress disease progression in some patients with autoimmune diseases. However, the mechanism underlying these long-term beneficial effects has remained unclear. Here, we evaluated Ig gene usage in patients with anti-myelin-associated glycoprotein (anti-MAG) neuropathy, an autoimmune disease of the peripheral nervous system that is mediated by IgM autoantibodies binding to MAG antigen. Patients with anti-MAG neuropathy showed substantial clonal expansions of blood IgM memory B cells that recognized MAG antigen. The group of patients showing no clinical improvement after rituximab therapy were distinguished from clinical responders by a higher load of clonal IgM memory B cell expansions before and after therapy, by persistence of clonal expansions despite efficient peripheral B cell depletion, and by a lack of substantial changes in somatic hypermutation frequencies of IgM memory B cells. We infer from these data that the effectiveness of rituximab therapy depends on efficient depletion of noncirculating B cells and is associated with qualitative immunological changes that indicate reconfiguration of B cell memory through sustained reduction of autoreactive clonal expansions. These findings support the continued development of B cell-depleting therapies for autoimmune diseases.

[Beneficial effects of rituximab in a case of anti-myelin antibody-associated neuropathy]

We report here in a 61-year-old woman in whom sensory disturbance predominantly affecting the distal portion of the limbs progressed over the course of 1 year. Blood tests showed IgM monoclonal gammopathy as well as the presence of anti-myelin-associated glycoprotein (MAG) antibody. Nerve conduction studies revealed significant prolongation of distal latency, and sural nerve biopsy showed IgM deposition on the myelin sheath. She was diagnosed as suffering anti-MAG neuropathy. High-dose intravenous immunoglobulin therapy proved to be ineffective and her symptoms progressed. Therefore, rituximab was administered and the sensory disturbance improved. Although no detailed studies on rituximab therapy for anti-MAG neuropathy have been reported in Japan, the present findings suggest that rituximab may be more effective than immunoglobulin therapy and other conventional therapies that have been used for autoimmune neuropathies.

The role of sulfoglucuronosyl glycosphingolipids in the pathogenesis of monoclonal IgM paraproteinemia and peripheral neuropathy

In IgM paraproteinemia and peripheral neuropathy, IgM M-protein secretion by B cells leads to a T helper cell response, suggesting that it is antibody-mediated autoimmune disease involving carbohydrate epitopes in myelin sheaths. An immune response against sulfoglucuronosyl glycosphingolipids (SGGLs) is presumed to participate in demyelination or axonal degeneration in the peripheral nervous system (PNS). SGGLs contain a 3-sulfoglucuronic acid residue that interacts with anti-myelin-associated glycoprotein (MAG) and the monoclonal antibody anti-HNK-1. Immunization of animals with sulfoglucuronosyl paragloboside (SGPG) induced anti-SGPG antibodies and sensory neuropathy, which closely resembles the human disease. These animal models might help to understand the disease mechanism and lead to more specific therapeutic strategies. In an in vitro study, destruction or malfunction of the blood-nerve barrier (BNB) was found, resulting in the leakage of circulating antibodies into the PNS parenchyma, which may be considered as the initial key step for development of disease.

Placebo-controlled trial of rituximab in IgM anti-myelin-associated glycoprotein antibody demyelinating neuropathy

OBJECTIVE

Report a double-blind, placebo-controlled study of rituximab in patients with anti-MAG demyelinating polyneuropathy (A-MAG-DP).

METHODS

Twenty-six patients were randomized to four weekly infusions of 375 mg/m(2) rituximab or placebo. Sample size was calculated to detect changes of > or = 1 Inflammatory Neuropathy Course and Treatment (INCAT) leg disability scores at month 8. IgM levels, anti-MAG titers, B cells, antigen-presenting cells, and immunoregulatory T cells were monitored every 2 months.

RESULTS

Thirteen A-MAG-DP patients were randomized to rituximab and 13 to placebo. Randomization was balanced for age, electrophysiology, disease duration, disability scores, and baseline B cells. After 8 months, by intention to treat, 4 of 13 rituximab-treated patients improved by > or = 1 INCAT score compared with 0 of 13 patients taking placebo (p = 0.096). Excluding one rituximab-randomized patient who had normal INCAT score at entry, and thus could not improve, the results were significant (p = 0.036). The time to 10m walk was significantly reduced in the rituximab group (p = 0.042) (intention to treat). Clinically, walking improved in 7 of 13 rituximab-treated patients. At month 8, IgM was reduced by 34% and anti-MAG titers by 50%. CD25+CD4+Foxp3+ regulatory cells significantly increased by month 8. The most improved patients were those with high anti-MAG titers and most severe sensory deficits at baseline.

INTERPRETATION

Rituximab is the first drug that improves some patients with A-MAG-DP in a controlled study. The benefit may be exerted by reducing the putative pathogenic antibodies or by inducing immunoregulatory T cells. The results warrant confirmation with a larger trial.

What's new in paraproteinemic demyelinating neuropathy in 2007-2008?

Research and development in the area of paraproteinemic demyelinating peripheral neuropathy is slower than for some of the other inflammatory neuropathy syndromes. However, 2007-2008 has produced developments in the understanding of the pathogenesis of the neuropathy and the paraprotein, a potential new animal model, easier diagnostics, and two randomized controlled trials with the results of others awaited. This short review summarizes these publications.

Induction of experimental ataxic sensory neuronopathy in cats by immunization with purified SGPG

IgM paraproteins in about 50% of the patients with neuropathy associated with IgM gammopathy react with carbohydrate moieties in myelin-associated glycoprotein (MAG) and in sulfated glucuronic glycolipids (SGGLs) in human peripheral nerves. However, the role of anti-MAG/SGGL antibodies in the pathogenesis of neuropathy remains unclear. In order to induce an animal model of neuropathy associated with anti-MAG/SGGL antibodies, cats were immunized with sulfoglucuronyl paragloboside (SGPG). All four cats immunized with SGPG developed clinical signs of sensory neuronopathy within 11 months after initial immunization, characterized by unsteadiness, falling, hind limb weakness and ataxia. In two cats the ataxia and hind limb paralysis were so severe that the animals had to be euthanized. Pathological examination revealed sensory ganglionitis with inflammatory infiltrates in the dorsal root ganglia. No overt signs of pathology were noted in the examined roots or nerves. High titer anti-SGPG/MAG antibodies were detected in all 4 cats immunized with SGPG but not in 3 control cats. Our data demonstrate that immunization of cats with SGPG induced anti-SGPG antibodies and sensory neuronopathy clinically resembling the sensory ataxia of patients with monoclonal IgM anti-MAG/SGPG antibodies. This study suggests that these anti-MAG/SGPG antibodies play a role in the pathogenesis of this neuropathy.

Immunotherapy for IgM anti-myelin-associated glycoprotein paraprotein-associated peripheral neuropathies

BACKGROUND

Serum monoclonal anti-myelin associated glycoprotein antibodies may be pathogenic in some people with IgM paraprotein and demyelinating neuropathy. Immunotherapies aimed at reducing the level of these antibodies might be expected to be beneficial.

OBJECTIVES

To examine the efficacy of any form of immunotherapy in reducing disability and impairment resulting from IgM anti-myelin associated glycoprotein paraprotein-associated demyelinating peripheral neuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Register (March 2005), MEDLINE (January 1966 to March 2005) and EMBASE (January 1980 to March 2005) for controlled trials. We also checked bibliographies and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomised or quasi-randomised controlled trials of participants of any age treated with any type of immunotherapy for anti-myelin-associated glycoprotein antibody associated demyelinating peripheral neuropathy with monoclonal gammopathy of undetermined significance of any severity. Our primary outcome measure was change in the Neuropathy Impairment Scale or Modified Rankin Scale at six months after randomisationSecondary outcome measures were: Neuropathy Impairment Scale or the Modified Rankin Score at 12 months after randomisation; ten-metre walk time, subjective clinical scores and electrophysiological parameters at six and 12 months after randomisation; IgM paraprotein levels and anti-myelin associated glycoprotein antibody titres at six months after randomisation and adverse effects of treatments.

DATA COLLECTION AND ANALYSIS

We identified eight possible trials. Of these, five randomised controlled trials were included after discussion between the authors. One author extracted and the other checked the data. No missing data could be obtained from trial authors.

MAIN RESULTS

The five eligible trials (97 participants) tested intravenous immunoglobulin, interferon-alpha or plasma exchange. Only two, of intravenous immunoglobulin, had comparable interventions and outcomes but both were short-term. There were no significant benefits of the treatments used in the outcomes predefined for this review, but not all the predefined outcomes were used in every included trial. Intravenous immunoglobulin showed benefits in terms of improvement in Modified Rankin Scale at two weeks and 10-metre walk time at four weeks. Serious adverse effects of intravenous immunoglobulin are known to occur from observational studies but none were encountered in these trials.

AUTHORS' CONCLUSIONS

There is inadequate reliable evidence from trials of immunotherapies in anti-myelin associated glycoprotein paraproteinaemic neuropathy to recommend any particular immunotherapy treatment. Intravenous immunoglobulin is relatively safe and may produce some short-term benefit. Large well-designed randomised trials of at least six to 12 months duration are required to assess existing or novel therapies.

Contribution of peptides to multiple sclerosis research

Multiple sclerosis (MS) is an autoimmune disease associated with chronic inflammatory demyelination of the central nervous system in genetically susceptible individuals. Because of the disease complexity and heterogeneity, its pathogenesis remains unknown despite extensive research efforts, and specific effective treatments have not yet been developed. Peptide-based research has been important in attempts to unravel particular aspects of this complex disease, including the characterization of the different molecular mechanisms of MS, with the goal of providing useful products for immune-mediated therapies. In fact, in the past decade, peptide-based research has been predominant in research aimed to identify and/or develop target antigens as synthetic probes for specific biomarkers as well as innovative immunomodulating therapies. This review presents an overview of the contributions of peptide science to MS research and discusses future directions of peptide-based investigations.

Autoantibody testing

Recent advances in neuroimmunology have led to improvements in the pathogenesis, diagnosis, prognosis, and treatment of many neuromuscular disorders. The value of autoantibody testing is increasing steadily in neurologic practice. Not all antibodies have a high yield in diagnosis. In some disorders, such as generalized adult onset of myasthenia gravis, Lambert-Eaton myasthenic syndrome,Miller Fisher syndrome, and multifocal motor neuropathy,autoantibody tests provide accurate diagnosis and can be considered biologic markers of these disorders.

Immunotherapy for IgM anti-Myelin-Associated Glycoprotein paraprotein-associated peripheral neuropathies

BACKGROUND

Serum monoclonal anti-Myelin Associated Glycoprotein antibodies may be pathogenic in some patients with IgM paraprotein and demyelinating neuropathy. Immunotherapies aimed at reducing the level of these antibodies might be expected to be of benefit in the treatment of the neuropathy. Many potential therapies have been described in small trials, uncontrolled studies and case reports.

OBJECTIVES

To examine the efficacy of any form of immunotherapy in reducing disability and impairment resulting from IgM anti-Myelin Associated Glycoprotein paraprotein-associated demyelinating peripheral neuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group register (August 2002) and MEDLINE (January 1966 - August 2002) and EMBASE (January 1980 - August 2002) for controlled trials, checked the bibliographies to identify other controlled trials and contacted authors and other experts in the field.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised controlled trials.

TYPES OF PARTICIPANTS

patients of any age with anti-Myelin Associated Glycoprotein antibody associated demyelinating peripheral neuropathy with monoclonal gammopathy of undetermined significance of any severity. Types of interventions: any type of immunotherapy. Types of outcome measures: Primary: improvement in the Neuropathy Disability Score or Modified Rankin Scale six months after randomisation Secondary: Neuropathy Disability Score and/or the Modified Rankin Score 12 months after randomisation. Ten metre walk time, subjective clinical scores and electrophysiological parameters at six and 12 months after randomisation. IgM paraprotein levels and anti-Myelin Associated Glycoprotein antibody titres six months after randomisation. Adverse effects of treatments.

DATA COLLECTION AND ANALYSIS

We identified six randomised controlled trials of which five were included after discussion between the authors. One author extracted the data and the other checked them. No missing data could be obtained from authors.

MAIN RESULTS

The five eligible trials used four of the many available immunotherapy treatments. Only two had comparable interventions and outcomes but these were only short-term studies. There were no significant benefits of the treatments used in the predefined outcomes. However intravenous immunoglobulin showed benefits in terms of improved Modified Rankin Scale at two weeks and 10 metre walk time at four weeks. Serious adverse effects of intravenous immunoglobulin are known to occur from observational studies but none were encountered in these trials.

REVIEWER'S CONCLUSIONS

There is inadequate reliable evidence from trials of immunotherapies in anti-Myelin Associated Glycoprotein paraproteinaemic neuropathy to recommend any particular immunotherapy treatment. Intravenous immunoglobulin is relatively safe and may produce some short-term benefit. Large well designed randomised trials are required to assess the efficacy of promising new therapies.

Generation and characterization of antibodies to sulfated glucuronyl glycolipids in Lewis rats

Antibodies to sulfated glucuronyl glycolipids (SGGLs) have been reported in sera of patients with peripheral neuropathies including patients with IgM gammopathy. However, the role of anti-SGGL antibodies in the pathogenesis of neuropathy remains unclear. In order to study the role of antibodies to SGGLs in the pathogenesis of neuropathy, Lewis female rats were injected with purified SGPG mixed with keyhole limpet hemocyanin (KLH) and emulsified with equal amount of complete Freund's adjuvant. High titer anti-SGPG antibodies were detected by ELISA in sera of all rats inoculated with SGPG. All anti-SGPG antibodies cross-reacted with human myelin-associated glycoprotein (MAG). None of the sensitized rats exhibited clinical signs of neuropathy. Histological examination showed that there was no demyelination or axonal damage in peripheral nerves. Our data demonstrate that SGPG is a highly immunogenic glycolipid but high titer antibodies against it do not produce an experimental autoimmune neuropathy in Lewis rats.

Multiple MAG peptides are recognized by circulating T and B lymphocytes in polyneuropathy and multiple sclerosis

Abnormal immune responses to myelin associated glycoprotein (MAG), a component of myelin of the central and peripheral nervous system, have been suggested to play a role in the pathogenesis of multiple sclerosis (MS) and certain types of inflammatory polyneuropathy. To identify possible immunodominant MAG peptides in neuroinflammation, we examined T and B cell responses to five selected synthetic MAG peptides and myelin proteins in 21 patients with non-inflammatory polyneuropathy, 26 patients with MS, 10 optic neuritis patients and 17 healthy subjects. Enzyme-linked immunosorbent spot-forming cell assays were adopted, allowing the detection and enumeration of individual antigen responsive T and B cells in body fluids. Patients with polyneuropathy as well as those with MS had elevated levels of T and B cells recognizing MAG and its peptides. Any of the five MAG peptides under study functioned as immunodominant T and/or B cell epitope in individual subjects. None of the MAG peptides elicited a specific disease-associated T or B cell response. The enhanced T and B cell response to myelin components like MAG may play some role in initiation and/or progression of these diseases, but they could also represent secondary responses associated with myelin damage and indicate tolerization rather than autoaggressive immunity.

Treatment experience in patients with anti-myelin-associated glycoprotein neuropathy

We report our experience with 24 consecutively treated patients (15 men and 9 women, median age 64 years) with anti-myelin-associated glycoprotein (anti-MAG) neuropathy. The rates of response to plasma exchange (40%), immune globulin (16%), and cyclophosphamide-based therapy (36%) were similar. Five (24%) responded to the first treatment modality, 32% to a second, alternative modality, and 31% to a third. Only 4 of 12 responders had sustained improvement; the others relapsed after a median of 7 months. In those 4 patients, the median immunoglobulin M (IgM) level dropped by 25% compared to an increase of 24% in the nonresponders (P = 0.04). Thus, most patients with anti-MAG neuropathy failed to have sustained improvement after treatment, and none of the therapies emerged as superior. Disability improved transiently after therapy in approximately 50% of cases. A 25% reduction of the IgM level predicted sustained improvement, but was difficult to achieve. There were no clinical or electrodiagnostic features associated with a treatment response, nor did a reduction of the anti-MAG antibody titer correlate with clinical improvement.