Diagnostics of anti-MAG antibody polyneuropathy

Lenalidomide in the treatment of anti-myelin-associated glycoprotein neuropathy: A phase 1 study to identify the maximum tolerated dose

BACKGROUND

Anti-myelin-associated glycoprotein (MAG) neuropathy is a debilitating demyelinating polyneuropathy with no approved therapies. Our primary objective was to ascertain lenalidomide safety and maximum tolerated dose (MTD) in anti-MAG neuropathy.

METHODS

This phase 1b, open-label, single-arm, dose-finding trial was conducted from 2019 through 2022. The original design included a dose-escalation/extension phase followed by a dose-expansion phase. Three doses of lenalidomide were evaluated: 10, 15, and 25 mg. The main outcome was the MTD.

RESULTS

Eleven patients enrolled (10 men), with a mean age of 67.6 years (SD = 6.18, range 58-77 years) and mean disease duration of 8.5 years (SD = 10.9, range 1-40 years). The study terminated early due to higher-than-expected non-dose-limiting toxicity venous thromboembolism (VTE) events. The calculated MTD was 25 mg (posterior mean of toxicity probability was 0.01 with a 95% credible interval of 0.00, 0.06), but a recommended phase 2 dose of 15 mg was advised. For secondary exploratory outcomes, only EQ-5D (-0.95, 95% CI -1.81 to -0.09) and total IgM (-162 mg/dL, 95% CI -298 to -26) showed signs of improvement by month 12.

CONCLUSIONS

Lenalidomide was associated with higher-than-expected VTE events in anti-MAG neuropathy patients, despite a calculated MTD of 25 mg. A recommended phase 2 dose of 15 mg was advised. Lenalidomide did not improve disability or impairment at 12 months, although this study was not powered for efficacy. The risks of long term lenalidomide may outweigh benefit for patients with anti-MAG neuropathy. Any future efficacy study should address VTE risk, as current myeloma guidelines appear inadequate.

TRIAL REGISTRATION

Lenalidomide in Anti-MAG Neuropathy: Phase 1b Study, ClinicalTrials.gov Identifier: NCT03701711, https://clinicaltrials.gov/ct2/show/NCT03701711. First submitted October 10, 2018. First patient enrolled in January 2019.

A novel cell-based immunofluorescence assay for the detection of autoantibodies to myelin-associated glycoprotein

Peripheral neuropathy with antibodies to myelin-associated glycoprotein (MAG) is an autoimmune demyelinating disorder of the peripheral nervous system caused by pathogenic IgM recognizing the human natural killer-1 glycoepitope expressed on MAG. This study aimed to analyze the performance of a new indirect immunofluorescence cell-based assay (CBA, EUROIMMUN) for the detection of anti-MAG IgM. Antibody reactivity was determined in sera from 95 patients with clinical and neurophysiological evidence of anti-MAG-associated neuropathy and in control samples from 55 patients with other forms of peripheral neuropathy. Compared to the results of the gold standard method (ELISA, Bühlmann) and using samples at a dilution of 1:100, the CBA had a sensitivity of 98.9% and a specificity of 100% (PPV 100%, NPV 98.2%). In conclusion, the CBA allows the detection of antibodies to MAG using an easy and standardized technique, and it presents a sensitive and specific alternative to the more time-consuming ELISA. Larger studies are needed to address anti-MAG titer monitoring in parallel with clinical activity.

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.

A diagnostic score for anti-myelin-associated-glycoprotein neuropathy or chronic inflammatory demyelinating polyradiculoneuropathy in patients with anti-myelin-associated-glycoprotein antibody

BACKGROUND AND PURPOSE

A diagnostic score was developed to discriminate anti-myelin-associated-glycoprotein (MAG) neuropathy from chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and applied it to patients with atypical anti-MAG neuropathy.

METHODS

The clinical and electrophysiological features of patients with a diagnosis of typical anti-MAG neuropathy were compared to those of patients with a diagnosis of CIDP. The association of each feature with the diagnosis was assessed in the two groups. Features showing a significant association with the diagnosis were included in a multivariable logistic regression model and adjusted odds ratios were estimated for each feature. A score ranging from 1 to 3 was applied to each feature based on the magnitude of the estimated odds ratios. The score was then applied to patients with a clinical diagnosis of CIDP who also had high anti-MAG antibody titers (CIDP-MAG).

RESULTS

Thirty-one anti-MAG neuropathy patients, 45 typical CIDP patients and 16 CIDP-MAG patients were included. Scores in anti-MAG antibody patients ranged from 1 to 5 and in CIDP patients from -7 to -1. Using the score, 4/16 CIDP-MAG patients were diagnosed to have anti-MAG neuropathy and 12/16 patients to have CIDP. Response to intravenous immunoglobulin in the CIDP-MAG patients classified as CIDP was similar to that of definite CIDP patients and higher than that of anti-MAG neuropathy patients.

CONCLUSIONS

Our score allowed an accurate discrimination to be made, amongst patients with anti-MAG antibodies, of those affected by CIDP and the patients with anti-MAG neuropathy. This score may help proper treatment to be chosen for patients with anti-MAG antibodies with a CIDP-like presentation.

[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.

Waldenström macroglobulinemia treatment algorithm 2018

Waldenström macroglobulinemia is often an indolent disorder, and many patients are candidates for observation with careful monitoring. For symptomatic patients, one must distinguish between those patients whose symptoms are related to immunologic manifestations associated with the IgM monoclonal protein and those that have symptoms related to progressive marrow and nodal infiltration with lymphoplasmacytic lymphoma. In Waldenström macroglobulinemia, the driver for therapy in the majority of patients is progressive anemia, secondary to bone marrow replacement by lymphoplasmacytic lymphoma. Recent introduction of MYD88 mutational analysis has been very useful for diagnostic purposes but is unclear what effect it might have on the prognosis or response rate to therapy. An algorithm is provided on the management of asymptomatic individuals and the sequence used for chemotherapeutic intervention of symptomatic patients.