IgM MGUS associated with anti-MAG neuropathy: a single institution experience

Inter-laboratory comparison of routine autoantibody detection methods for autoimmune neuropathies and myasthenia gravis

Serological tests are important to detect autoantibodies (autoAbs) in patients with autoimmune neuropathies (AN) and myasthenia gravis (MG) as they are biomarkers for diagnosis, stratification, treatment selection, and monitoring. However, tests to detect autoAbs frequently lack proper standardization and results differ across diagnostic laboratories. We compared results for tests routinely performed in Spanish diagnostic laboratories to detect AN and MG autoAbs. In the Spanish Society of Immunology Autoimmunity Group national workshop, serum samples from 13 patients with AN or MG were tested for anti-ganglioside, anti-myelin-associated glycoprotein (MAG), anti-nicotinic acetylcholine receptor (AChR), and anti-muscle-specific kinase (MuSK) autoAbs using reference methods and were distributed for analysis to 27 participating laboratories using their routine methods. Overserved were inter-laboratory variability and worryingly low sensitivity, especially for anti-ganglioside immunoglobulin G and anti-MAG autoAb detection. This pilot study reflects autoAbs detection state of the art in AN and MG testing in leading diagnostic laboratories in Spain, highlighting the need for standardization prior to clinical use.

IgM monoclonal gammopathy of undetermined significance: clinicopathologic features with and without IgM-related disorders

A subset of patients with immunoglobulin M (IgM) monoclonal gammopathy of undetermined significance (MGUS) develop IgM-related disorders (IgM-RD) including peripheral neuropathy, cryoglobulinemia and/or cold agglutinin disease (CAD). We examined the clinical and bone marrow pathologic findings in 191 IgM MGUS patients (2016 World Health Oragnization criteria). Clonal plasma cells were identified in 41 of 171 (24%) cases by immunohistochemistry (IHC) and clonal B cells in 43 of 157 (27%). IgM-RD was identified in 82 (43%) cases, including peripheral neuropathy (n=67, 35%), cryoglobulinemia (n=21, 11%), and CAD (n=10, 5%). Cases of CAD showed distinctive features including lack of MYD88 mutations (P=0.048), supporting the concept of primary CAD as a distinct clinicopathologic disorder. Following exclusion of CAD, comparison of the remaining cases with (n=72) or without (n=109) IgM-RD showed IgM-RD to be more frequent in men than women (P=0.02) and to be more highly associated with MYD88 L265P (P=0.011). Cases with and without IgM-RD otherwise showed similar features including serum IgM concentrations, presence of lymphoid aggregates, clonal B cells by flow cytometry or clonal plasma cells by IHC. No differences were observed in overall survival between cases with and without IgM-RD. No cases in this series met criteria for plasma cell type IgM MGUS as defined in the 2022 International Consensus Classification of lymphoid neoplasms. These results show IgM-RD to be common in patients with IgM MGUS. While CAD shows distinctive features, the remaining cases of IgM-RD largely show pathologic findings similar to IgM MGUS without IgM-RD.

Value of Antibody Determinations in Chronic Dysimmune Neuropathies

Chronic dysimmune neuropathies encompass a group of neuropathies that share immune-mediated pathomechanism. Chronic dysimmune antibody-related neuropathies include anti-MAG neuropathy, multifocal motor neuropathy, and neuropathies related to immune attack against paranodal antigens. Such neuropathies exhibit distinguishing pathomechanism, clinical and response to therapy features with respect to chronic inflammatory demyelinating polyradiculoneuropathy and its variants, which represent the most frequent form of chronic dysimmune neuropathy. This narrative review provides an overview of pathomechanism; clinical, electrophysiological, and biochemical features; and treatment response of the antibody-mediated neuropathies, aiming to establish when and why to look for antibodies in chronic dysimmune neuropathies.

Efficacy of rituximab in anti-myelin-associated glycoprotein demyelinating polyneuropathy: Clinical, hematological and neurophysiological correlations during 2 years of follow-up

BACKGROUND AND PURPOSE

We evaluated the clinical and neurophysiological efficacy of rituximab (RTX) in a neurophysiologically homogeneous group of patients with monoclonal gammopathy and immunoglobulin M (IgM) anti-myelin-associated glycoprotein antibody (anti-MAG) demyelinating polyneuropathy.

METHODS

Twenty three anti-MAG-positive polyneuropathic patients were prospectively evaluated before and for 2 years after treatment with RTX 375 mg/m² . The Inflammatory Neuropathy Cause and Treatment (INCAT) disability scale (INCAT-ds), modified INCAT sensory score (mISS), Medical Research Council sum score, Patients' Global Impression of Change scale were used, IgM levels were assessed and extensive electrophysiological examinations were performed before (T0) and 1 year (T1) and 2 years (T2) after RTX treatment.

RESULTS

At T1 and T2 there was a significant reduction from T0 both in mISS and in INCAT-ds, with a p value < 0.001 in the inferential Friedman's test overall analysis. Ulnar nerve Terminal Latency Index and distal motor latency significantly changed from T0 to T1 and in the overall analysis (p = 0.001 and p = 0.002), and ulnar nerve sensory nerve action potential (SNAP) amplitude was significantly increased at T2 from T1, with a p value < 0.001 in the overall analysis. Analysis of the receiver-operating characteristic curves showed that a 41.8% increase in SNAP amplitude in the ulnar nerve at T2 from T0 was a fair predictor of a mISS reduction of ≥2 points (area under the curve 0.85; p = 0.005; sensitivity: 90.9%, specificity: 83.3%).

CONCLUSIONS

This study suggests that RTX is effective in patients with clinically active demyelinating anti-MAG neuropathy over 2 years of follow-up, and that some neurophysiological variables might be useful for monitoring this efficacy.

Decrease in Serum Anti-MAG Autoantibodies Is Associated With Therapy Response in Patients With Anti-MAG Neuropathy: Retrospective Study

Background and Objectives

The objective of the retrospective analysis was to test the hypothesis that changes in serum anti-myelin-associated glycoprotein (MAG) autoantibodies are associated with clinical response to immunotherapy in patients with anti-MAG neuropathy.

Methods

As of January 29, 2020, we used anti-myelin-associated glycoprotein-related search strings in the Medline database to identify studies that provided information on anti-MAG immunoglobulin M (IgM) autoantibodies and clinical outcomes during immunotherapies. The relative change in anti-MAG IgM titers, paraprotein levels, or total IgM was determined before, during, or posttreatment, and the patients were assigned to “responder,” “nonresponder,”’ or “acute deteriorating” category depending on their clinical response to treatment. The studies were qualified as “supportive” or “not supportive” depending on the percentage of patients exhibiting an association between relative change of anti-MAG antibody titers or levels and change in clinical outcomes.

Results

Fifty studies with 410 patients with anti-MAG neuropathy were included in the analysis. Forty studies with 303 patients supported the hypothesis that a “responder” patient had a relative reduction of anti-MAG antibody titers or levels that is associated with clinical improvements and “nonresponder” patients exhibited no significant change in anti-MAG IgM antibodies. Six studies with 93 patients partly supported, and 4 studies with 26 patients did not support the hypothesis.

Discussion

The retrospective analysis confirmed the hypothesis that a relative reduction in serum anti-MAG IgM antibodies is associated with a clinical response to immunotherapies; a sustained reduction of at least 50% compared with pretreatment titers or levels could be a valuable indicator for therapeutic response.

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.

Type-I Cryoglobulinaemia Associated to Monoclonal Gammapathy of Undetermined Significance

Cryoglobulins are immunoglobulins that undergo reversible precipitation at cold temperatures. Monoclonal type-I cryoglobulinaemia is the least frequent and is associated to hematological diseases such as multiple myeloma, Waldenström's macroglobulinaemia, chronic lymphocytic leukaemia and lymphoma. We describe the case of a 60-year-old female patient, who suffered from burning pain in her feet for ten months before her admission. The patient presented intermittent distal cyanosis that progressed to digital ischaemia. She also reported paresthesia in her hands, difficulty in writing, and a 26-kg-weight loss. At the physical examination, it was identified livedo reticularis, palpable purpura, and painful ecchymotic lesions in her calves and feet. Moreover, peripheral pulses were palpable and symmetrical. It was observed an atrophy of the right first dorsal interosseous and both extensor digitorum brevis, as well as a distal bilateral apalesthesia and allodynia. Both Achilles reflexes were absent. Laboratory tests revealed anemia, high erythrosedimentation rate and C-reactive protein. Serum protein electrophoresis showed a monoclonal IgG-Kappa gammopathy. The results also evidenced the presence of Bence-Jones proteinuria. The bone marrow biopsy revealed less than 10% of plasma cells, and skin biopsy informed leukocytoclastic vasculitis. The patient was treated with high-dose intravenous steroids and cyclophosphamide. The treatment showed that the skin lesions had improved, pain disappeared and motor deficit stopped its progression.

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.

Autoantibody Diagnostics in Neuroimmunology: Experience From the 2018 Italian Neuroimmunology Association External Quality Assessment Program

Background: Neuroimmunology has impressively expanded in the past decade. Novel assays, especially cell-based assays (CBAs) can detect conformational antibodies (Abs) recognizing antigens in their native conformation. Generally, the availability of in-house and of commercial tests has improved the diagnostics, but introduced demanding laboratory tasks. Hence, standardization and quality controls represent a key step to promote accuracy. We report on the results of the 2018 external quality assessment program (EQAP) organized by the Italian Neuroimmunology Association.

Methods: EQAP regarded 10 schemes, including oligoclonal bands (OCBs), intracellular-neuronal (ICN)-Abs, neuronal-surface (NS)-Abs, aquaporin-4 (AQP4)-Abs, myelin oligodendrocyte glycoprotein (MOG)-Abs, myelin-associated glycoprotein (MAG)-Abs, ganglioside-Abs, acetylcholine-receptor (AChR)-Abs, and muscle-specific-kinase (MuSK)-Abs, and 34 laboratories. Assays were classified as tissue-based assays (TBAs), solid-phase assays (SPAs), liquid-phase assays (LPAs), and CBAs. Thirty-three samples were provided.

Results: Three-quarter of the tests were commercial. Median accuracy for the laboratories was 75% (range 50–100). In 8/10 schemes, at least one sample provided discrepant results. Inter-laboratory “substantial agreement” was found in 6/10 schemes (AChR, MuSK, MAG, AQP4, MOG, and NS-Abs), whereas the worst agreements regarded OCBs and ganglioside-Abs. Both commercial and in-house assays performed better in experienced laboratories.

Conclusions: Assays could be divided in (a) robust commercial tests with substantial inter-laboratory agreement (MAG-Abs; AChR- and MuSK-Abs); commercial/“in-house” tests with (b) partial inter-laboratory agreement (AQP4-Abs, MOG-Abs, NS-Abs, ICN-Abs), and (c) with large inter-laboratory disagreement (OCBs, ganglioside-Abs). This real-life snapshot of the neuroimmunology test performances highlights shortcomings attributable to technician-dependent performances, assay structural limitations, and errors in test interpretations.

Distinctive patterns of peripheral neuropathy across the spectrum of plasma cell disorders

Many patients with plasma cell disorders suffer from peripheral neuropathy, but differential diagnosis with chronic inflammatory demyelinating polyneuropathy (CIDP) is difficult. We aimed to (1) identify factors useful for differential diagnosis between peripheral neuropathy associated with plasma cell disorders versus CIDP and (2) determine whether neuropathy presentations and severity varied across the spectrum of different plasma cell disorders. A retrospective chart review of 18 monoclonal gammopathy of unknown significance (MGUS) patients, 15 POEMS syndrome patients and 34 CIDP patients between January 2005 and December 2016 was conducted. The peripheral neuropathy associated with plasma cell disorders seemed to be more sensory oriented compared to CIDP. MGUS patients were significantly older than CIDP patients (median age 70 vs. 59, respectively, p = 0.027). POEMS syndrome patients showed significantly higher platelet count at the time of neuropathy presentation compared to CIDP (p = 0.028). Lambda type MGUS patients were associated with less severe symptoms compared to POEMS syndrome patients despite harboring lambda monoclonal gammopathy as a common denominator. Kappa type MGUS patients showed predominantly axonal type neuropathy compared to its counterpart and POEMS syndrome. Careful inspection of clinical profiles and symptoms of patients presenting with neuropathy can help to discriminate those with underlying plasma cell disorders. The phenotype of neuropathy, platelet count and age at presentation seem to be the most useful indicators.

[Anti-myelin-associated glycoprotein antibody positive IgM monoclonal gammopathy related peripheral neuropathy: 11 cases and literature review]

Objective: To improve the understanding of rare anti-myelin-associated glycoprotein (MAG) positive IgM monoclonal gammopathy related peripheral neuropathy (IgM-PN) . Methods: Eleven cases of IgM paraproteinemia and anti-MAG antibody positive neuropathy diagnosed since 2014 in Peking Medical Union College Hospital were summarized. The medical records including clinical manifestation, lab results, treatment and prognosis were analyzed. Results: Among the 11 patients (8 male and 3 female) , the median onset age is 63 years old (range from 52 to 77 years old) . The peripheral neuropathy of 9 patients were characterized by distal onset of numbness, 6 patients suffered from muscle weakness. The nerve conduction velocity study indicated that all 11 patients had demyelinating peripheral nerve damage, which was sensory predominant and more severe in lower limbs, 6 of them had secondary axonal damage. Monoclonal IgM gammopathy was identified in all 11 patients, among which 6 were IgM κ, 2 IgG κ and IgM κ bi-clonal, 3 IgM λ. Three patients were diagnosed with Waldenström's macroglobulinaemia. The anti-MAG-IgM antibody was positive in all 11 cases. After diagnosis, 9 patients received combination chemotherapy including rituximab or rituximab treatment alone. The monoclonal IgM level declined significantly in 7 patients. The neuropathy was stable or improved. Conclusions: Anti-MAG antibody positive IgM-PN is a rare M protein related disease. In peripheral neuropathy with undetermined etiology, we suggest to screen M protein and anti-MAG antibody. Chemotherapy including rituximab or rituximab alone is recommended as first-line therapy.

Serum markers in the differential diagnosis of Waldenstrom macroglobulinemia and other IgM monoclonal gammopathies

BACKGROUND

IgM monoclonal gammopathy can be present in a broad spectrum of diseases. We evaluated the value of serum markers in the differential diagnosis of Waldenstrom macroglobulinemia (WM) and other types of IgM monoclonal gammopathies.

METHODS

We included patients who were first admitted to hospital and identified as having IgM monoclonal gammopathy by serum immunofixation electrophoresis (sIFE). We evaluated basic clinical features, sIFE, diagnosis, and serum markers. Furthermore, we applied the receiver operating characteristic (ROC) curve to analyze the differential diagnosis value of serum markers for WM. Finally, we used logistic regression and ROC curve to analyze the differential diagnosis value of multimarker combinations to identify WM.

RESULTS

IgM monoclonal gammopathy was most frequently found in patients with Waldenstrom macroglobulinemia, followed by monoclonal gammopathy of undetermined significance (MGUS), B-cell non-Hodgkin Lymphoma (B-NHL), and multiple myeloma (MM). Serum markers showed significant differences among the four diseases. The diagnostic markers LDH, IgM, IgG, IgA, and serum light chain К had higher diagnostic efficiency. Among these markers, serum IgM provided the highest diagnostic efficiency. Additionally, the combined use of all five serum markers provided the most effective diagnosis.

CONCLUSIONS

The five serum markers, LDH, IgM, IgG, IgA, and К, each yielded a specific efficacy in differential diagnosis of WM. The single marker with the highest diagnostic efficiency was the serum IgM level. However, a combination of multiple serum markers was better than the use of a single marker in diagnosing WM. The combined use of all five serum markers provided the most effective diagnosis, with an AUC of .952 and sensitivity and specificity of 87.8% and 86.9%, respectively.

Monoclonal IgM Gammopathy and Waldenström's Macroglobulinemia

BACKGROUND

3.2-3.5% of persons over age 50 have a monoclonal gammopathy. Monoclonal gammopathies have many causes, including cancer. 10-20% of monoclonal gammopathies are of isotype IgM. A systematic approach to the differential diagnosis of IgM gammopathies is essential because of the different therapeutic implications of the various underlying conditions.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed and current guidelines from Germany and abroad.

RESULTS

The diagnosis of a monoclonal IgM gammopathy is established by serum electrophoresis in combination with immune fixation. Further evaluation enables the identification of the underlying condition: the differential diagnosis includes IgM-MGUS (monoclonal gammopathy of unclear significance), Waldenström's disease, and IgM myeloma. The therapeutic implications of the under - lying condition vary from watchful waiting in IgM-MGUS to combined rituximab and antineoplastic chemotherapy (off-label first-line use of rituximab) in symptomatic Waldenström's macroglobulinemia. Ibrutinib has been approved for the treatment of patients with recurrences, or of those for whom first-line treatment with rituximab and chemotherapy is not suitable. The current treatment options do not result in cure. In symptomatic Waldenström's disease, the goal of treatment is to keep the disease under control for as long as possible without impairing the patient's quality of life.

CONCLUSION

Evidence-based treatment decisions in Waldenström's macroglobulinemia now rely mainly on small-scale, single-armed trials. Patients with this disease should be treated in the setting of a clinical trial if possible. Trials aimed at improving the quality of treatment for other IgM-associated diseases, such as IgM neuropathies and cold agglutinin disease, would also be desirable.

Diagnostics of anti-MAG antibody polyneuropathy

This document presents the guidelines for anti-myelin-associated glycoprotein (MAG) antibody testing that have been developed following a consensus process built on questionnaire-based surveys, internet contacts, and discussions at workshops of sponsoring Italian Association of Neuroimmunology (AINI) congresses. The main clinical information on anti-MAG antibody polyneuropathy, indications and limits of anti-MAG antibody testing, instructions for result interpretation, and an agreed laboratory protocol (Appendix) are reported for the communicative community of neurologists and clinical pathologists.

IgMk paraprotein from gammopathy patient can bind to cardiolipin and interfere with coagulation assay: a case report

Background

The monoclonal gammopathies are a group of plasma-cell proliferative disorders characterized by the secretion of monoclonal immunoglobulin (M protein or paraprotein). Some rare cases have revealed the specific affinity of paraprotein as autoantibody. Here we report a patient with monoclonal gammopathy of undetermined significance (MGUS) accompanied by a remarkable increase of anticardiolipin antibody (aCL) and an extensively decreased coagulation factor activity, however, without any clinical signs of antiphospholipid syndrome (APS) and bleeding.

Results

Our further investigation indicated that IgMκ paraprotein of this patient possessed an antibody activity against phospholipids so as to bind to cardiolipin and interfere with coagulation assay in vitro.

Conclusions

This case might be indicative that an abnormality of coagulation tests, disturbed by IgMκ paraprotein, does not predict a risk of bleeding in this patient.

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.

Monoclonal gammopathy: The good, the bad and the ugly

Monoclonal gammopathy of undetermined significance (MGUS) is a condition characterized by the presence of a monoclonal gammopathy (MG) in which the clonal mass has not reached a predefined state in which the condition is considered malignant. It is a precursor to conditions such as multiple myeloma or lymphoma at a rate of ~1%/year. Thus, from a hematologic standpoint, MGUS is a fairly benign condition. However, it is now recognized that organ damage resulting from just the MG without the need MM or lymphoma can occur. One of the most recognized is nephropathy secondary to monoclonal gammopathy of renal significance (MGRS). Other well-recognized conditions include neuropathies, oculopathies and dermopathies. Some conditions such as autoimmune diseases and coagulopathies are less common and recognized. Finally, systemic involvement of multiple organs is well described in several entities. In all of these conditions, the role of the MG is no longer insignificant. Thus, the term MGUS should be avoided when describing these entities.