Clinical outcomes in multifocal motor neuropathy: A combined cross-sectional and follow-up study

Multifocal motor neuropathy in Japan: A nationwide survey on prevalence, clinical profiles, and treatment

INTRODUCTION/AIMS

Multifocal motor neuropathy (MMN) is a rare disease for which epidemiological and clinical data are limited. We conducted a nationwide survey to determine disease prevalence, incidence, clinical profile, and current treatment status in Japan.

METHODS

A nationwide survey was conducted in 2021 using an established epidemiological method. Questionnaires were sent to all neurology and pediatric neurology departments in Japan. An initial questionnaire was administered to determine the number of patients with and incidence of MMN. A second questionnaire was administered to collect detailed clinical information. The European Federation of Neurological Societies/Peripheral Nerve Society 2010 guidelines were used as diagnostic criteria.

RESULTS

The estimated number of patients with MMN was 507. The estimated prevalence was 0.40 per 100,000 individuals. Detailed clinical profiles were available for 120 patients. The male-to-female ratio was 2.3:1 and the median onset age was 42 years. The median disease duration at diagnosis was 25 months. Most patients presented with upper limb-dominant muscle weakness. Motor nerve conduction blocks were found in 62% of patients and positive anti-GM1 IgM antibody results in 54%. A total of 117 (98%) patients received immunoglobulin therapy, and 91% of them showed improvement. At the time of the last visit (median, 82 months from treatment initiation), 89 (74%) patients were receiving maintenance immunoglobulin therapy. A slight progression of neurological deficits was observed during follow-up.

DISCUSSION

Most patients with MMN in Japan received induction and maintenance immunoglobulin therapies, which appear to suppress long-term disease progression.

Therapeutic potentials of adoptive cell therapy in immune-mediated neuropathy

Immune-mediated neuropathy (IMN) is a group of heterogenous neuropathies caused by intricate autoimmune responses. For now, known mechanisms of different IMN subtypes involve the production of autoantibodies, complement activation, enhanced inflammation and subsequent axonal/demyelinating nerve damages. Recent therapeutic studies mainly focus on specific antibodies and small molecule inhibitors previously approved in rheumatoid diseases. Initial strategies based on the pathophysiologic features of IMN should be explored. Adoptive cell therapy (ACT) refers to the emerging immunotherapies in which circulating immunocytes are collected from peripheral blood and modified with killing and immunomodulatory capacities. It consists of chimeric antigen receptor-T cell therapy, T cell receptor-engineered T cell, CAR-Natural killer cell therapy, and others. In the last decade, ACT has demonstrated extraordinary potentials in treating cancers, infectious diseases and autoimmune diseases. Versatile combinations of targets, chimeric domains and effector cells greatly empower ACT to treat complicated immune disorders. In this review, we summarized the advances of ACT and envisioned suitable strategies for different IMN subtypes.

A 21-bp deletion in the complement regulator CD55 promotor region is associated with multifocal motor neuropathy and its disease course

BACKGROUND AND AIMS

To further substantiate the role of antibody-mediated complement activation in multifocal motor neuropathy (MMN) immunopathology, we investigated the distribution of promotor polymorphisms of genes encoding the membrane-bound complement regulators CD46, CD55, and CD59 in patients with MMN and controls, and evaluated their association with disease course.

METHODS

We used Sanger sequencing to genotype five common polymorphisms in the promotor regions of CD46, CD55, and CD59 in 133 patients with MMN and 380 controls. We correlated each polymorphism to clinical parameters.

RESULTS

The genotype frequencies of rs28371582, a 21-bp deletion in the CD55 promotor region, were altered in patients with MMN as compared to controls (p .009; Del/Del genotype 16.8% vs. 7.7%, p .005, odds ratio: 2.43 [1.27-4.58]), and patients carrying this deletion had a more favorable disease course (mean difference 0.26 Medical Research Council [MRC] points/year; 95% confidence interval [CI]: 0.040-0.490, p .019). The presence of CD59 rs141385724 was associated with less severe pre-diagnostic disease course (mean difference 0.940 MRC point/year; 95% CI: 0.083-1.80, p .032).

INTERPRETATION

MMN susceptibility is associated with a 21-bp deletion in the CD55 promotor region (rs2871582), which is associated with lower CD55 expression. Patients carrying this deletion may have a more favorable long-term disease outcome. Taken together, these results point out the relevance of the pre-C5 level of the complement cascade in the inflammatory processes underlying MMN.

IgM anti-GM2 antibodies in patients with multifocal motor neuropathy target Schwann cells and are associated with early onset

BACKGROUND

Multifocal motor neuropathy (MMN) is a rare, chronic immune-mediated polyneuropathy characterized by asymmetric distal limb weakness. An important feature of MMN is the presence of IgM antibodies against gangliosides, in particular GM1 and less often GM2. Antibodies against GM1 bind to motor neurons (MNs) and cause damage through complement activation. The involvement of Schwann cells (SCs), expressing GM1 and GM2, in the pathogenesis of MMN is unknown.

METHODS

Combining the data of our 2007 and 2015 combined cross-sectional and follow-up studies in Dutch patients with MMN, we evaluated the presence of IgM antibodies against GM1 and GM2 in serum from 124 patients with MMN and investigated their binding to SCs and complement-activating properties. We also assessed the relation of IgM binding and complement deposition with clinical characteristics.

RESULTS

Thirteen out of 124 patients (10%) had a positive ELISA titer for IgM anti-GM2. Age at onset of symptoms was significantly lower in MMN patients with anti-GM2 IgM. IgM binding to SCs correlated with IgM anti-GM2 titers. We found no correlation between IgM anti-GM2 titers and MN binding or with IgM anti-GM1 titers. IgM binding to SCs decreased upon pre-incubation of serum with soluble GM2, but not with soluble GM1. IgM anti-GM2 binding to SCs correlated with complement activation, as reflected by increased C3 fixation on SCs and C5a formation in the supernatant.

CONCLUSION

Circulating IgM anti-GM2 antibodies define a subgroup of patients with MMN that has an earlier onset of disease. These antibodies probably target SCs specifically and activate complement, similarly as IgM anti-GM1 on MNs. Our data indicate that complement activation by IgM antibodies bound to SCs and MNs underlies MMN pathology.

Evidence for spontaneous regulation of the humoral IgM anti-GM1 autoimmune response by IgG antibodies in multifocal motor neuropathy patients

BACKGROUND AND AIMS

Multifocal motor neuropathy (MMN) is a peripheral nerve disorder characterized by slow progressive distal asymmetric weakness with minimal or no sensory impairment. Currently, a vast evidence supports a direct pathogenic role of IgM anti-GM1 antibodies on disease pathogenesis. Patients with MMN seropositive for GM1-specific IgM antibodies have significantly more weakness, disability and axon loss than patients without these antibodies. During the screening for IgM anti-GM1 antibodies in a cohort of patients with neuropathy we noticed an absence or significant reduction of natural IgM anti-GM1 autoreactivity in some patients with MMN, suggesting a mechanism of self-control of autoreactivity. We aim to understand the lack of natural reactivity against GM1 in MMN patients.

METHODS

The presence of free IgM anti-GM1 reactivity or its complex to blocking IgG was analysed by combining high performance thin layer chromatography-immunostaining, soluble binding inhibition assays, Protein-G or GM1-affinity columns and dot blot assays.

RESULTS

We identified in MMN patients an immunoregulation of IgM anti-GM1 antibodies mediated by IgG immunoglobulins characterized by: (i) lack of natural IgM anti-GM1 autoreactivity as a result of a immunoregulatory IgG-dependent mechanism; (ii) presence of natural and disease-associated IgM anti-GM1/IgG blocking Ab complexes in sera; and (iii) high levels of IgG blocking against natural IgM anti-GM1 antibodies (Abs.

INTERPRETATION

Our observations unmask a spontaneous IgG-dependent mechanism of immunoregulation against IgM anti-GM1 antibodies that could explain, in part, fluctuations in the usually slowly progressive clinical course that characterizes the disease and, at the same time, allows the identification of an autoimmune response against GM1 ganglioside in seronegative patients.

Multifocal motor neuropathy is not associated with altered innate immune responses to endotoxin

OBJECTIVE

Antibody- and complement-mediated peripheral nerve inflammation are central in the pathogenesis of MMN. Here, we studied innate immune responses to endotoxin in patients with MMN and controls to further our understanding of MMN risk factors and disease modifiers.

METHODS

We stimulated whole blood of 52 patients with MMN and 24 controls with endotoxin and collected plasma. With a multiplex assay, we determined levels of the immunoregulating proteins IL-1RA, IL-1β, IL-6, IL-10, IL-21, TNF-α, IL-8 and CD40L in unstimulated and LPS-stimulated plasma. We compared baseline and stimulated protein levels between patients and controls and correlated concentrations to clinical parameters.

RESULTS

Protein level changes after stimulation were comparable between groups (p > 0.05). IL-1RA, IL-1β, IL-6 and IL-21 baseline concentrations showed a positive correlation with monthly IVIg dosage (all corrected p-values < 0.016). Patients with anti-GM1 IgM antibodies showed a more pronounced IL-21 increase after stimulation (p 0.048).

CONCLUSIONS

Altered endotoxin-induced innate immune responses are unlikely to be a susceptibility factor for MMN.

Autoimmune polyneuropathies

The autoimmune peripheral neuropathies with prominent motor manifestations are a diverse collection of unusual peripheral neuropathies that are appreciated in vast clinical settings. This chapter highlights the most common immune-mediated, motor predominant neuropathies excluding acute, and chronic inflammatory demyelinating polyradiculoneuropathy (AIDP and CIDP, respectively). Other acquired demyelinating neuropathies such as distal CIDP and multifocal motor neuropathy will be covered. Additionally, the radiculoplexus neuropathies, resulting from microvasculitis-induced injury to nerve roots, plexuses, and nerves, including diabetic and nondiabetic lumbosacral radiculoplexus neuropathy and neuralgic amyotrophy (i.e., Parsonage-Turner syndrome), will be included. Finally, the motor predominant peripheral neuropathies encountered in association with rheumatological disease, particularly Sjögren's syndrome and rheumatoid arthritis, are covered. Early recognition of these distinct motor predominant autoimmune neuropathies and initiation of immunomodulatory and immunosuppressant treatment likely result in improved outcomes.

Plexus MRI helps distinguish the immune-mediated neuropathies MADSAM and MMN

BACKGROUND

Among immune-mediated neuropathies, clinical-electrophysiological overlap exists between multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) and multifocal motor neuropathy (MMN). Divergent immune pathogenesis, immunotherapy response, and prognosis exist between these two disorders. MRI reports have not shown distinction of these disorders, but biopsy confirmation is lacking in earlier reports. MADSAM nerves are hypertrophic with onion bulbs, inflammation, and edema, whereas MMN findings are limited to multifocal axonal atrophy.

OBJECTIVES

To understand if plexus MRI can distinguish MADSAM from MMN among pathologically (nerve biopsy) confirmed cases.

METHODS

Retrospective chart review and blinded plexus MRI review of biopsy-confirmed MADSAM and MMN cases at Mayo Clinic.

RESULTS

Nine brachial plexuses (MADSAM-5, MMN-4) and 6 lumbosacral plexuses (MADSAM-4, MMN-2) had fascicular biopsies of varied nerves. Median follow-up in MADSAM was 93 months (range: 7-180) and 27 (range: 12-109) in MMN (p = 0.34). MRI hypertrophy occurred solely in MADSAM (89%, 8/9) with T2-hyperintensity in both. There was no correlation between time to imaging for hypertrophy, symptom onset age, or motor neuropathy impairments (mNIS). At last follow-up, on diverse immunotherapies mNIS improved in MADSAM (median - 4, range: -22 to 0), whereas MMN worsened (median 3, range: 0 to 6, p = 0.03) on largely IVIG.

CONCLUSION

Nerve hypertrophy on plexus MRI helps distinguish MMN from MADSAM, where better immunotherapy treatment outcomes were observed. These findings are consistent with the immune pathogenesis seen on biopsies. Radiologic distinction is possible independent of time to imaging and extent of motor deficits, suggesting MRI is helpful in patients with uncertain clinical-electrophysiologic diagnosis, especially motor-onset MADSAM.

MRI of the intraspinal nerve roots in patients with chronic inflammatory neuropathies: abnormalities correlate with clinical phenotypes

OBJECTIVE

Chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN) are caused by inflammatory changes of peripheral nerves. It is unknown if the intra-spinal roots are also affected. This MRI study systematically visualized intra-spinal nerve roots, i.e., the ventral and dorsal roots, in patients with CIDP, MMN and motor neuron disease (MND).

METHODS

We performed a cross-sectional study in 40 patients with CIDP, 27 with MMN and 34 with MND. All patients underwent an MRI scan of the cervical intra-spinal roots. We systematically measured intra-spinal nerve root sizes bilaterally in the transversal plane at C5, C6 and C7 level. We calculated mean nerve root sizes and compared them between study groups and between different clinical phenotypes using a univariate general linear model.

RESULTS

Patients with MMN and CIDP with a motor phenotype had thicker ventral roots compared to patients with CIDP with a sensorimotor phenotype (p = 0.012), while patients with CIDP with a sensory phenotype had thicker dorsal roots compared to patients with a sensorimotor phenotype (p = 0.001) and with MND (p = 0.004).

CONCLUSION

We here show changes in the morphology of intra-spinal nerve roots in patients with chronic inflammatory neuropathies, compatible with their clinical phenotype.

Motor unit integrity in multifocal motor neuropathy: A systematic evaluation with CMAP scans

Introduction/Aims

Progressive axonal loss in multifocal motor neuropathy (MMN) is often assessed with nerve conduction studies (NCS), by recording maximum compound muscle action potentials (CMAPs). However, reinnervation maintains the CMAP amplitude until a significant portion of the motor unit (MU) pool is lost. Therefore, we performed more informative CMAP scans to study MU characteristics in a large cohort of patients with MMN.

Methods

We derived the maximum CMAP amplitude (CMAP_max), an MU number estimate (MUNE), and the largest MU amplitude stimulus current required to elicit 5%, 50%, and 95% of CMAP_max (S5, S50, S95) and relative ranges ([S95 − S5] × 100 / S50) from the scans. These metrics were compared with clinical, laboratory, and NCS results.

Results

Forty MMN patients and 24 healthy controls were included in the study. CMAP_max and MUNE were reduced in MMN patients (both P < .001). Largest MU amplitude as a percentage of CMAP_max was increased in MMN patients (P < .001). Disease duration and treatment duration were not associated with MUNE. Relative range was larger in patients with anti‐GM1 antibodies than in those without anti‐GM1 antibodies (P = .016) and controls (P < .001). The largest MU amplitudes were larger in patients without anti‐GM1 antibodies than in patients with anti‐GM1 antibodies (P = .037) and controls (P = .044).

Discussion

We found that MU loss is common in MMN and accompanied by enlarged MUs. Presence of anti‐GM1 antibodies was associated with increased relative range of MU thresholds and reduction in largest MU amplitude. Our findings indicate that CMAP scans complement routine NCS, and may have potential for practical monitoring of treatment efficacy and disease progression.

Anti-C2 Antibody ARGX-117 Inhibits Complement in a Disease Model for Multifocal Motor Neuropathy

Background and Objectives

To determine the role of complement in the disease pathology of multifocal motor neuropathy (MMN), we investigated complement activation, and inhibition, on binding of MMN patient-derived immunoglobulin M (IgM) antibodies in an induced pluripotent stem cell (iPSC)-derived motor neuron (MN) model for MMN.

Methods

iPSC-derived MNs were characterized for the expression of complement receptors and membrane-bound regulators, for the binding of circulating IgM anti-GM1 from patients with MMN, and for subsequent fixation of C4 and C3 on incubation with fresh serum. The potency of ARGX-117, a novel inhibitory monoclonal antibody targeting C2, to inhibit fixation of complement was assessed.

Results

iPSC-derived MNs moderately express the complement regulatory proteins CD46 and CD55 and strongly expressed CD59. Furthermore, MNs express C3aR, C5aR, and complement receptor 1. IgM anti-GM1 antibodies in serum from patients with MMN bind to MNs and induce C3 and C4 fixation on incubation with fresh serum. ARGX-117 inhibits complement activation downstream of C4 induced by patient-derived anti-GM1 antibodies bound to MNs.

Discussion

Binding of IgM antibodies from patients with MMN to iPSC-derived MNs induces complement activation. By expressing complement regulatory proteins, particularly CD59, MNs are protected against complement-mediated lysis. Yet, because of expressing C3aR, the function of these cells may be affected by complement activation upstream of membrane attack complex formation. ARGX-117 inhibits complement activation upstream of C3 in this disease model for MMN and therefore represents an intervention strategy to prevent harmful effects of complement in MMN.

Pure Motor Onset and IgM-Gammopathy Occurrence in Multifocal Acquired Demyelinating Sensory and Motor Neuropathy

BACKGROUND AND OBJECTIVES

To longitudinally investigate patients with multifocal acquired demyelinating sensory and motor neuropathy (MADSAM), quantifying timing and location of sensory involvements in motor onset patients, along with clinicohistopathologic and electrophysiologic findings to ascertain differences in patients with and without monoclonal gammopathy of uncertain significance (MGUS).

METHODS

Patients with MADSAM seen at Mayo Clinic and tested for monoclonal gammopathy and ganglioside antibodies were retrospectively reviewed (January 1, 2007-December 31, 2018).

RESULTS

Of 76 patients with MADSAM, 53% had pure motor, 16% pure sensory, 30% sensorimotor, and 1% cranial nerve onsets. Motor-onset patients were initially diagnosed with multifocal motor neuropathy (MMN). MGUS occurred in 25% (89% immunoglobulin M [IgM] subtype), associating with ganglioside autoantibodies (p < 0.001) and higher IgM titers (p < 0.04). Median time to sensory involvements (confirmed by electrophysiology) in motor onset patients was 18 months (range 6-180). Compared to initial motor nerve involvements, subsequent sensory findings were within the same territory in 35% (14/40), outside in 20% (8/40), or both in 45% (18/40). Brachial and lumbosacral plexus MRI was abnormal in 87% (34/39) and 84% (21/25), respectively, identifying hypertrophy and increased T2 signal predominantly in brachial plexus trunks (64%), divisions (69%), and cords (69%), and intrapelvic sciatic (64%) and femoral (44%) nerves. Proximal fascicular nerve biopsies (n = 9) more frequently demonstrated onion-bulb pathology (p = 0.001) and endoneurial inflammation (p = 0.01) than distal biopsies (n = 17). MRI and biopsy findings were similar among patient subgroups. Initial Inflammatory Neuropathy Cause and Treatment (INCAT) disability scores were higher in patients with MGUS relative to without (p = 0.02). Long-term treatment responsiveness by INCAT score reduction ≥1 or motor Neuropathy Impairment Score (mNIS) >8-point reduction occurred in 75% (49/65) irrespective of MGUS or motor onsets. Most required ongoing immunotherapy (86%). Patients with MGUS more commonly required dual-agent immunotherapy for stability (p = 0.02).

DISCUSSION

Pure motor onsets are the most common MADSAM presentation. Long-term follow-up, repeat electrophysiology, and nerve pathology help distinguish motor onset MADSAM from MMN. Better long-term immunotherapy responsiveness occurs in motor onset MADSAM compared to MMN reports. Patients with MGUS commonly require dual immunotherapy.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that most clinical, electrophysiologic, and histopathologic findings were similar between patients with MADSAM with and without MGUS.

SMN1 Duplications Are Associated With Progressive Muscular Atrophy, but Not With Multifocal Motor Neuropathy and Primary Lateral Sclerosis

Objective

To assess the association between copy number (CN) variation in the survival motor neuron (SMN) locus and multifocal motor neuropathy (MMN), progressive muscular atrophy (PMA), and primary lateral sclerosis (PLS) susceptibility and to determine the association of SMN1 and SMN2 CN with MMN, PMA, and PLS disease course.

Methods

In this monocenter study, we used multiplex ligation-dependent probe amplification to determine SMN1 and SMN2 CN in Dutch patients with MMN, PMA, and PLS and controls. We stratified clinical parameters for SMN1 and SMN2 CN. We analyzed SMN1 and SMN2 exons 1–6, intron 6, and exon 8 CN to study the genetic architecture of SMN1 duplications.

Results

SMN1 and SMN2 CN were determined in 132 patients with MMN, 150 patients with PMA, 104 patients with PLS, and 956 control subjects. MMN and PLS were not associated with CN variation in SMN1 or SMN2. By contrast, patients with PMA more often than controls carried SMN1 duplications (≥3 SMN1 copies, 12.0% vs 5.0%, odds ratio 2.69 (1.43–4.91), p 0.0020). SMN1 and SMN2 CN status was not associated with MMN, PLS, or PMA disease course. In case of SMN1 exon 7 duplications, exons 1–6, exon 8, and introns 6 and 7 were also duplicated, suggesting full SMN1 duplications.

Conclusions

SMN1 duplications are associated with PMA, but not with PLS and MMN. SMN1 duplications in PMA are balanced duplications. The results of this study highlight the primary effect of altered SMN CN on lower motor neurons.

What is in the Literature

This edition of What is in the Literature focuses on chronic immune neuropathies as they represent treatable conditions. There are formal criteria to solidify the diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), but patients are encountered who have clinical and electrodiagnostic features of CIDP but do not fulfill diagnostic criteria. These patients are addressed in recent publications. CIDP (and variants) and other forms of immune-mediated neuropathies (multifocal motor neuropathy) are responsive early on to treatment, but long-term factors are less well described, and a number of publications focus on extended consequences. Acute immune neuropathies have been described in the setting of viral illness, and recent publications look at the question as to whether they are associated with the COVID-19 pandemic. Finally, idiopathic sensory neuropathies are the most common polyneuropathy, and consensus efforts to codify features into subtypes can be used clinically for a more precise diagnosis.

Changes of clinical, neurophysiological and nerve ultrasound characteristics in CIDP over time: a 3-year follow-up

OBJECTIVES

To evaluate, in a prospective study, high-resolution ultrasound (HRUS) changes of nerve segments in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and their relationships with clinical and electrodiagnostic (EDX) characteristics.

METHODS

Twenty-three consecutive patients with CIDP were included in a 3-year follow-up (FU) study. Each patient underwent neurologic examination, EDX and HRUS study. HRUS was performed on median, ulnar and peroneal nerves, yielding a total of 319 scanned nerve segments. INCAT and MRC-sum scores, motor nerve conduction velocity (NCV), compound muscle action potential (cMAP) amplitude, and nerve cross-sectional area (NCSA) were collected at baseline and at FU end, and were used for statistical analysis. Twenty-two healthy individuals, matched to patients for age and BMI, served as controls.

RESULTS

NCSA was higher in patients than in controls (p < 0.0001) and showed significant direct correlation with disease severity, and inverse correlation with NCV and cMAP amplitude, both at baseline and at FU end. Disease duration, clinical scores and EDX were predictors of NCSA enlargement at both time points. During FU, NCSA increased in 51% of nerve segments (p = 0.006), in correlation with INCAT increase and with NCV and cMAP reduction. Considering EDX changes in subgroups that reflect the different types of nerve damage, NCSA significantly increased in those nerve segments that from normal EDX switched to prevalent myelinopathic EDX characteristics.

CONCLUSIONS

Peripheral nerve size tends to increase over time in patients with CIDP, in correlation with clinical and EDX changes, in particular in those nerve segments that undergo a predominantly demyelinating damage.