Functioning and quality of life in patients with neuropathy associated with anti-MAG antibodies

Validity and Responsiveness of Balance Measurements Using Posturography in Patients With Immune-Mediated Neuropathies

BACKGROUND AND AIMS

Validated objective measures for balance in immune mediated neuropathies are lacking. In this study, we investigated the clinimetric properties of posturography using a force platform, a quantitative assessment of postural control.

METHODS

We assessed patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and IgM-related polyneuropathy (IgM-PNP) using sway parameters (path, area and amplitude) measured at multiple time points. Validity was investigated by assessing differences in sway path between patients with and without reported balance symptoms and by assessing correlations of sway path with (established) impairment measures related to balance, disability and quality of life (QoL). Responsiveness was assessed by means of an anchor-based approach, using a patient anchor and two disability scales.

RESULTS

We included 52 CIDP and 13 IgM-PNP patients. In CIDP, sway path was 25% longer in patients reporting balance symptoms relative to patients without balance symptoms (p = 0.03). There was excellent reliability between consecutive measurements in both CIDP and IgM-PNP. Moderate to good correlations were observed between sway path and an ataxia scale (CIDP: Spearman's ρ = 0.46, 95% CI: 0.2-0.69; IgM-PNP: Spearman's ρ = 0.72, 95% CI: 0.28-0.96) while correlations with related disability measures and QoL were poor. Changes in sway parameters over time were not consistently associated with changes in other outcome measures.

INTERPRETATION

Posturography measurements showed poor validity and responsiveness. Therefore, despite excellent reliability, using a force platform in clinical practice or trials for immune-mediated neuropathies cannot be recommended.

Neuropathy with anti-myelin-associated glycoprotein antibodies: update on diagnosis, pathophysiology and management

Antimyelin-associated glycoprotein (MAG) neuropathy is a rare autoimmune demyelinating peripheral neuropathy caused by IgM autoantibodies targeting MAG. The typical presentation is that of a slowly progressive, distal, length-dependent, predominantly sensory, sometimes ataxic neuropathy, frequently accompanied by upper limb tremor. Distal motor weakness may subsequently occur. The clinical presentation may vary and rarely be consistent with that of typical chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), as well as have an aggressive and rapidly disabling course. The diagnosis of anti-MAG neuropathy is based on the detection of anti-MAG antibodies through ELISA or western blot analysis, primarily in presence of an IgM monoclonal gammopathy. Anti-MAG neuropathy may occur without or with haematological malignancy. Electrophysiology is characteristic of a predominantly distal demyelinating neuropathy. Intravenous immunoglobulins and plasma exchange have unproven benefits, but may provide short-term effects. Cytotoxic therapies are commonly used, although without an evidence base. Rituximab, an anti-B-cell monoclonal antibody was studied in two randomised controlled trials, neither of which achieved their primary outcome. However, a meta-analysis of these two studies demonstrated improvement of disability at 8-12 months. A recent trial with lenalidomide was interrupted prematurely due to a high rate of venous thromboembolism. There are currently two ongoing trials with Bruton's tyrosine kinase inhibitors. Symptom control is otherwise frequently needed. Outcome measures used for other inflammatory neuropathies present limitations in anti-MAG neuropathy. International registries such as the planned IMAGiNe study may, in future, provide answers to the many remaining questions.

Optimizing Anti-Myelin-Associated Glycoprotein and IgM-Gammopathy Testing for Neuropathy Treatment Evaluation

BACKGROUND AND OBJECTIVES

Patients with typical anti-myelin-associated glycoprotein (anti-MAG) neuropathy have IgM-gammopathy, mimic distal chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), and are treatment resistant. Anti-MAG patients go unrecognized when IgM-gammopathy is undetected or with atypical phenotypes. We investigated an optimal anti-MAG titration cutoff for excluding CIDP and the impact of IgM-gammopathy detection on neuropathy treatment evaluation without anti-MAG antibodies.

METHODS

European Academy of Neurology/Peripheral Nerve Society 2021 guidelines were used to assess patients with neuropathy using anti-MAG Bühlmann titration units (BTU) and IgM-gammopathy with Mass-Fix (mass spectrophotometry) and serum protein immunofixation electrophoresis (SPIEP). The immunotherapy outcome was reviewed by inflammatory neuropathy cause and treatment (INCAT) and summated compound muscle action potential (CMAP) nerve conduction changes.

RESULTS

Seven hundred and fifty-two patients (average age: 63.8 years, female: 31%) were identified over 30 months: (1) typical anti-MAG neuropathy (n = 104); (2) atypical anti-MAG neuropathy (n = 13); (3) distal or sensory-predominant CIDP (n = 25), including 7 without IgM-gammopathy; (4) typical CIDP (n = 47), including 36 without IgM-gammopathy; (5) axonal IgM-gammopathy-associated neuropathy (n = 104); and (6) IgM-gammopathy-negative, anti-MAG-negative axonal neuropathies (n = 426); and (7) without neuropathy (n = 33) anti-MAG negative. IgM-gammopathy was evaluated by Mass-Fix (n = 493), SPIEP (n = 355), or both (n = 96). Mass-Fix detected 4 additional IgM-gammopathies (3%, 4/117) among patients with anti-MAG antibodies and 7 additional patients (2%, 7/376) without anti-MAG not detected by SPIEP testing. Immunotherapy follow-up was available in 123 (mean: 23 months, range: 3-120 months) including 47 with CIDP (28 without IgM-gammopathy) and 76 non-CIDP (5 without IgM-gammopathy, 45 anti-MAG positive). Treatments included IVIG (n = 89), rituximab (n = 80), and ibrutinib or zanubrutinib (n = 24). An optimal anti-MAG-positive cutoff was identified at ≥1,500 BTU (78% sensitivity, 96% specificity) and at ≥10,000 BTU (74% sensitivity, 100% specificity) for typical anti-MAG neuropathy. Improvements in INCAT scores (p < 0.0001) and summated CMAP (p = 0.0028) were associated with negative anti-MAG (<1,500 BTU, n = 78) and absence of IgM-gammopathy (n = 34). Among 47 patients with electrodiagnostically confirmed CIDP, all anti-MAG negative, the presence of IgM-gammopathy (n = 19) also correlated with a worse treatment response (INCAT scores p = 0.035, summated CMAP p = 0.049).

DISCUSSION

A cutoff of 10,000 BTU seems optimal for typical anti-MAG neuropathy while ≥1,500 BTU reduces the likelihood of immune-treatable CIDP. Mass-Fix improves IgM-gammopathy detection in anti-MAG and other IgM-gammopathy neuropathies. Patients with IgM-gammopathy lacking MAG antibodies show reduced treatment response.

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.

Validity, responsiveness, floor and ceiling effects of the Berg Balance Scale in patients with Guillain-Barré syndrome

We investigated the measurement properties of the Berg Balance Scale in patients with Guillain-Barré syndrome. A retrospective analysis was performed of 81 patients with Guillain-Barré syndrome of age 17-84 years who had completed inpatient rehabilitation over a 5-year period. They were assessed with the Berg Balance Scale, the 10 Meter Walk Test, and the 6 Minute Walk Test at admission and discharge. The concurrent validity of the Berg Balance Scale was confirmed by very good correlations with the 10 Meter Walk Test at admission and discharge (ρ = 0.83 and 0.78, respectively) and by excellent and very good correlations with the 6 Minute Walk Test at admission (ρ = 0.91) and discharge (ρ = 0.77). The predictive validity of the Berg Balance Scale for the 10 Meter Walk Test and the 6 Minute Walk Test at discharge was moderate (ρ = 0.62 and 0.61, respectively) and very good (ρ = -0.87) for length of stay. The minimal clinically important difference of the Berg Balance Scale was estimated to be 10 points. The scale was highly responsive to changes in balance (Cohen's d 0.9). No floor effect was identified. A ceiling effect was identified only at discharge. The Berg Balance Scale is feasible in patients with Guillain-Barré syndrome at admission and discharge from rehabilitation. However, a ceiling effect may occur at discharge in patients with high levels of balance.

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.

Berg balance scale as a tool for choosing the walking aid for patients with Guillain-Barré syndrome or polyneuropathy

Berg balance scale (BBS) is a widely used outcome measure in rehabilitation. We wanted to check if it can discriminate among levels of use of walking aid in patients with Guillain-Barré syndrome or polyneuropathy. A retrospective audit of 109 such patients (aged 16-85 years) who had completed inpatient rehabilitation in the period 2012-2017 was conducted. Receiver operating characteristic curve analysis was used to estimate the thresholds that optimise the prediction of the patient's walking aid. Statistically, significant threshold BBS score was estimated for the ability to walk without walking aid (≥49 points, yielding 88% sensitivity, 68% specificity and 83% classification accuracy) and the necessity to walk with a walker (≤37 points, yielding 62% sensitivity, 83% specificity and 78% classification accuracy). BBS score thresholds can therefore help clinicians choose the appropriate walking aid for patients with Guillain-Barré syndrome or polyneuropathy undergoing rehabilitation.

Wearable Health Technology to Quantify the Functional Impact of Peripheral Neuropathy on Mobility in Parkinson's Disease: A Systematic Review

The occurrence of peripheral neuropathy (PNP) is often observed in Parkinson’s disease (PD) patients with a prevalence up to 55%, leading to more prominent functional deficits. Motor assessment with mobile health technologies allows high sensitivity and accuracy and is widely adopted in PD, but scarcely used for PNP assessments. This review provides a comprehensive overview of the methodologies and the most relevant features to investigate PNP and PD motor deficits with wearables. Because of the lack of studies investigating motor impairments in this specific subset of PNP-PD patients, Pubmed, Scopus, and Web of Science electronic databases were used to summarize the state of the art on PNP motor assessment with wearable technology and compare it with the existing evidence on PD. A total of 24 papers on PNP and 13 on PD were selected for data extraction: The main characteristics were described, highlighting major findings, clinical applications, and the most relevant features. The information from both groups (PNP and PD) was merged for defining future directions for the assessment of PNP-PD patients with wearable technology. We established suggestions on the assessment protocol aiming at accurate patient monitoring, targeting personalized treatments and strategies to prevent falls and to investigate PD and PNP motor characteristics.

Quality of life in patients with polyneuropathy associated with different types of monoclonal gammopathy of undetermined significance

Polyneuropathy associated with monoclonal gammopathy of undetermined significance (MGUS-PNP) has a chronic and slowly progressive course but can lead to significant disability and reduced quality of life (QoL). The aim of this study was to analyze QoL in MGUS-PNP patients and to determine its predictors. Our study included 51 patients diagnosed with MGUS-PNP (23.5% with IgM, 66.7% IgG or IgA, 7.8% undetermined paraprotein, 2.0% light chains). QoL was assessed using the SF-36 questionnaire. The Medical Research Council Sum Score (MRC-SS), INCAT disability and sensory scores, ataxia score, Krupp's Fatigue Severity Scale and Beck's Depression Inventory were also used. Total SF-36 score was 50.0 ± 21.4 and no difference was observed between IgM and IgG/IgA MGUS-PNP. Physical composite score was worse than mental (44.4 ± 21.4 vs. 54.5 ± 20.9). Following factors showed correlation with SF-36 total score in univariate analysis: INCAT disability score, MRC-SS, INCAT sensory score, level of ataxia, fatigue and depression (p < 0.01). Significant predictors of worse SF-36 total score in our MGUS-PNP patients were depression (β = - 0.46, p < 0.01), fatigue (β = - 0.32, p < 0.01) and INCAT disability score (β = - 0.27, p < 0.01). QoL in MGUS-PNP is equally affected in patients with different types of paraprotein. MGUS-PNP patients with more severe functional disability, fatigue and depression need special attention of clinicians since they could be at higher risk to have worse QoL. This should be taken into account when treating subjects with MGUS-PNP.

Multidimensional evaluation is necessary to assess hand function in patients with Charcot-Marie-Tooth disease type 1A

BACKGROUND

Charcot-Marie-Tooth (CMT) disease type 1A (CMT1A) is the most common hereditary neuropathy. Several studies have assessed the relation between axonal loss and grip strength; however, the functional impact on dexterity and health-related quality of life (HRQoL) is unknown. We hypothesized that the severity of axonal loss will be correlated with loss of function and HRQoL.

OBJECTIVE

The purpose of this study was to evaluate the relation between severity of electroneuromyography impairment and its impact on function and HRQoL in adults with CMT1A.

METHODS

Grip and lateral pinch strength were evaluated with specific dynamometers: the Jamar and the Pinch Gauge. Dexterity was explored with the Sollerman, Jebsen, and Nine-hole Peg tests. The CMT impact on well-being was assessed by the validated Medical Outcomes Study Short Form 36 (SF-36), Beck Depression Inventory, and Fatigue Severity Scale, and disease severity by the CMT neuropathy score and Inflammatory Neuropathy Cause and Treatment sensory sum score. Finally, axonal loss and demyelination process was assessed by electroneuromyography.

RESULTS

We included 33 participants with CMT1A (23 females, mean [SD] age 47.0 [4.7] years). We found lack of correlation between severe electroneuromyography impairment (frequency of abnormal results >80%), significant distal amyotrophy (70%) and quality of life (mean [SD] scores for physical and mental SF-36 36.4 [10.0] and 48.4 [11.5]), autonomy for activities of daily living, and hand function that remains relatively preserved. We found a correlation between lateral pinch and dexterity according to the Sollerman test (r=0.52, p<0.05) but a lack of correlation among the other parameters.

CONCLUSIONS

Electrophysiological follow-up seems to be of little relevance to follow HRQoL in individuals with CMT1A and manual function related to functional objectives for everyday physical medicine and rehabilitation practice. The manual function is complex and requires an overall, quantitative, qualitative and multidisciplinary assessment. Each tool (Pinch Gauge, Jamar, Sollerman, Jebsen, Nine-hole Peg) measures a specific element of manual function and is necessary when performing a grip function analysis.

Prognostic factor of poor outcome in anti-MAG neuropathy: clinical and electrophysiological analysis of a French Cohort

BACKGROUND

Anti-MAG polyneuropathy (anti-MAG PN) is an immune-mediated peripheral sensorimotor neuropathy characterized by distal demyelination and ataxia. However, this disorder, unlike other immune-mediated neuropathies, is difficult to treat in most cases.

METHOD

We retrospectively collected all anti-MAG PN patients followed in two hospitals for a period of 12 years to determine prognostic factors, especially those that indicated a good response to the various therapeutic strategies used.

RESULTS

Forty-seven patients were included in the study; of these, 61% had a classical 'distal demyelinating pattern', 34.2% had a 'CIDP-like pattern', and the others had an 'axonal pattern'. The most commonly used treatments were intravenous immunoglobulin (IVIg) as the first-line treatment and rituximab as the second- or third-line treatment. No prognostic factor was identified for IVIg, but electrophysiological parameters at onset were better in patients with a good response to rituximab than in non-responder patients, even though mild or high disability was observed in nearly half the patients at last examination.

CONCLUSION

Even though disability seems to progress in most cases despite the treatments used, our results suggest that an early electrophysiological reduction in sensory nerves could be considered a 'red flag' for the prompt initiation of rituximab to try to delay long-term disability.

Limitations in daily activities and general perception of quality of life: Long term follow-up in patients with anti-myelin-glycoprotein antibody polyneuropathy

In this study, we assessed the modifications over time of daily activities and quality of life (QoL) in 32 subjects with anti-myelin-glycoprotein (MAG) antibody neuropathy. A widespread panel including clinical scores and patient-reported questionnaires, in compliance of the terms by the International Classification of Functioning, Disability, and Health (ICF) of the World Health Organization (WHO), was employed at enrollment (T0) and at follow-up evaluation (T1) after a mean interval of 15.4 ± 5.7 months. The Sensory Modality Sum score (SMS) at four limbs showed a significant worsening over time (mean score 27.2 ± 3.9 at T0 vs 25.7 ± 3 at T1 at upper limbs, P = .03; 20.5 ± 4.8 at T0 vs 18.6 ± 5.9 at T1 at lower limbs, P = .04). The Visual Analogue Scale (VAS) for pain significantly worsened at upper limbs at T1 (mean values 0.84 ± 1.95 at T0 vs 1.78 ± 2.6 at T1, P = .03). All the other tests did not show significant differences between T0 and T1. In the subgroup who underwent rituximab (15/32 treated before T0, 3/32 patients treated between T0 and T1 with median interval of 1 year), no significant differences were observed between T0 and T1. Despite the quite long follow-up, statistical significance was not achieved either for the limited number of patients or for the lack of sensitive outcome measures. In our cohort, the significant worsening of the SMS and VAS after a median of 14 months can be considered as a reliable expression of the natural history of the disease, and suggest that these scales might represent possible outcome measures in anti-MAG antibody neuropathy.