Nerve biopsy: Current indications and decision tools.

After initial investigation of patients presenting with symptoms suggestive of neuropathy, a clinical decision is made for a minority of patients to undergo further assessment with nerve biopsy. Many nerve biopsies do not demonstrate a definitive pathological diagnosis and there is considerable cost and morbidity associated with the procedure. This highlights the need for appropriate selection of patients, nerves and neuropathology techniques. Additionally, concomitant muscle and skin biopsies may improve the diagnostic yield in some cases. Several advances have been made in diagnostics in recent years, particularly in genomics. The indications for nerve biopsy have consequently changed over time. This review explores the current indications for nerve biopsies and some of the issues surrounding its use. Also included are comments on alternative diagnostic modalities that may help to supplant or reduce the use of nerve biopsy as a diagnostic test. These primarily include extraneural biopsy and neuroimaging techniques such as magnetic resonance neurography and nerve ultrasound. Finally, we propose an algorithm to assist in deciding when to perform nerve biopsies.

Nerve biopsy in acquired neuropathies.

A diagnosis of neuropathy can typically be determined through clinical assessment and focused investigation. With technological advances, including significant progress in genomics, the role of nerve biopsy has receded over recent years. However, making a specific and, in some cases, tissue-based diagnosis is essential across a wide array of potentially treatable acquired peripheral neuropathies. When laboratory investigations do not suggest a definitive diagnosis, nerve biopsy remains the final step to ascertain the etiology of the disease. The present review highlights the utility of nerve biopsy in confirming a diagnosis, while further illustrating the importance of a tissue-based diagnosis in relation to treatment strategies, particularly when linked to long-term immunosuppressive therapies.

Vasculitic neuropathy: Comparison of clinical predictors with histopathological outcome.

INTRODUCTION: To improve diagnostic accuracy, in this study we compared prebiopsy clinical parameters with subsequent pathological confirmation of peripheral nerve vasculitis. METHODS: Clinical, laboratory, and neurophysiological parameters were analyzed for consecutive patients referred for nerve biopsy with suspected vasculitis. Patients were assigned pathological categories of definite, probable, possible, or absent vasculitis using validated guidelines. Patients with definite or probable vasculitis were considered to have pathologically confirmed vasculitis. RESULTS: From a cohort of 78 patients, biopsy confirmed vasculitis in 29.5%. Parameters that best differentiated between pathologically confirmed and pathologically unlikely vasculitis were stepwise clinical progression (34.8% vs. 5.6%), the presence of serum anti-myeloperoxidase antibody (28.6% vs. 2.2%) and rheumatoid factor seropositivity (38.1% vs. 10.7%). Pathologically absent vasculitis was frequent in patients with normal (100%) or primarily demyelinating (87.5%) nerve conduction studies. DISCUSSION: Factoring the negative predictors of pathologically confirmed vasculitis into decision-making can reduce the frequency of diagnostically unhelpful nerve biopsies. Muscle Nerve 59:643-649, 2019.

Incidence and prevalence of NMOSD in Australia and New Zealand.

OBJECTIVES: We have undertaken a clinic-based survey of neuromyelitis optica spectrum disorders (NMOSDs) in Australia and New Zealand to establish incidence and prevalence across the region and in populations of differing ancestry. BACKGROUND: NMOSD is a recently defined demyelinating disease of the central nervous system (CNS). The incidence and prevalence of NMOSD in Australia and New Zealand has not been established. METHODS: Centres managing patients with demyelinating disease of the CNS across Australia and New Zealand reported patients with clinical and laboratory features that were suspicious for NMOSD. Testing for aquaporin 4 antibodies was undertaken in all suspected cases. From this group, cases were identified who fulfilled the 2015 Wingerchuk diagnostic criteria for NMOSD. A capture-recapture methodology was used to estimate incidence and prevalence, based on additional laboratory identified cases. RESULTS: NMOSD was confirmed in 81/170 (48%) cases referred. Capture-recapture analysis gave an adjusted incidence estimate of 0.37 (95% CI 0.35 to 0.39) per million per year and a prevalence estimate for NMOSD of 0.70 (95% CI 0.61 to 0.78) per 100 000. NMOSD was three times more common in the Asian population (1.57 (95% CI 1.15 to 1.98) per 100 000) compared with the remainder of the population (0.57 (95% CI 0.50 to 0.65) per 100 000). The latitudinal gradient evident in multiple sclerosis was not seen in NMOSD. CONCLUSIONS: NMOSD incidence and prevalence in Australia and New Zealand are comparable with figures from other populations of largely European ancestry. We found NMOSD to be more common in the population with Asian ancestry.

A new era in the treatment of multiple sclerosis.

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system with a multifactorial aetiology and highly variable natural history. A growing understanding of the immunopathogenesis of the condition has led to an expanding array of therapies for this previously untreatable disease. While a cure for MS remains elusive, the potential to reduce inflammatory disease activity by preventing relapses and minimising disease progression is achievable. The importance of early treatment in minimising long-term disability is increasingly recognised. Most of the newer, more effective therapies are associated with risks and practical problems that necessitate an active management strategy and continuous vigilance. While the initiation of these therapies is likely to remain the responsibility of neurologists, other specialist physicians and general practitioners will be involved in the identification and management of adverse effects.

Severe treatment-refractory antibody positive autoimmune autonomic ganglionopathy after mRNA COVID19 vaccination.

BACKGROUND: COVID-19 vaccine-associated peripheral and central neuroimmunological disorders have been well described. We present the case of a 56 year old male who developed α3-ganglionic AChR antibody positive Autoimmune Autonomic Ganglionopathy (AAG) after completion of a two-dose course of mRNA (Comirnaty) vaccination for COVID19. RESULTS: A previously hypertensive 56 year old male presented with the subacute onset of severe constipation, urinary retention, erectile dysfunction, sudomotor failure, sicca symptoms, non-reactive pupils and severe orthostatic hypotension shortly after receiving the second dose of an mRNA vaccine against COVID19. Autonomic testing revealed severe cardiovagal, adrenergic and sudomotor impairment, and tonic 'half-mast' pupils with evidence of sympathetic and parasympathetic denervation. Pathological α3-ganglionic ACHR antibodies were positive in serum as detected by a new flow cytometric immunomodulation assay. Malignancy was excluded. The patient was diagnosed with severe, treatment-refractory acute AAG. CONCLUSIONS: While autonomic dysfunction has been previously reported post-COVID19 vaccination, to our knowledge this is the first reported case of antibody-positive AAG in this setting. The severity of this case is in marked contrast to the existing literature on idiopathic antibody-positive autoimmune pandysautonomia.

A Flow Cytometric Assay to Detect Functional Ganglionic Acetylcholine Receptor Antibodies by Immunomodulation in Autoimmune Autonomic Ganglionopathy.

Autoimmune Autonomic Ganglionopathy (AAG) is an uncommon immune-mediated neurological disease that results in failure of autonomic function and is associated with autoantibodies directed against the ganglionic acetylcholine receptor (gnACHR). The antibodies are routinely detected by immunoprecipitation assays, such as radioimmunoassays (RIA), although these assays do not detect all patients with AAG and may yield false positive results. Autoantibodies against the gnACHR exert pathology by receptor modulation. Flow cytometric analysis is able to determine if this has occurred, in contrast to the assays in current use that rely on immunoprecipitation. Here, we describe the first high-throughput, non-radioactive flow cytometric assay to determine autoantibody mediated gnACHR immunomodulation. Previously identified gnACHR antibody seronegative and seropositive sera samples (RIA confirmed) were blinded and obtained from the Oxford Neuroimmunology group along with samples collected locally from patients with or without AAG. All samples were assessed for the ability to cause gnACHR immunomodulation utilizing the prototypical gnACHR expressing cell line, IMR-32. Decision limits were calculated from healthy controls, and Receiver Operating Characteristic (ROC) curves were constructed after unblinding all samples. One hundred and ninety serum samples were analyzed; all 182 expected negative samples (from healthy controls, autonomic disorders not thought to be AAG, other neurological disorders without autonomic dysfunction and patients with Systemic Lupus Erythematosus) were negative for immunomodulation (<18%), as were the RIA negative AAG and unconfirmed AAG samples. All RIA positive samples displayed significant immunomodulation. There were no false positive or negative samples. There was perfect qualitative concordance as compared to RIA, with an Area Under ROC of 1. Detection of Immunomodulation by flow cytometry for the identification of gnACHR autoantibodies offers excellent concordance with the gnACHR antibody RIA, and overcomes many of the shortcomings of immunoprecipitation assays by directly measuring the pathological effects of these autoantibodies at the cellular level. Further work is needed to determine the correlation between the degree of immunomodulation and disease severity.

Electrodiagnostic assessment of the autonomic nervous system: A consensus statement endorsed by the American Autonomic Society, American Academy of Neurology, and the International Federation of Clinical Neurophysiology.

Evaluation of disorders of the autonomic nervous system is both an art and a science, calling upon the physician's most astute clinical skills as well as knowledge of autonomic neurology and physiology. Over the last three decades, the development of noninvasive clinical tests that assess the function of autonomic nerves, the validation and standardization of these tests, and the growth of a large body of literature characterizing test results in patients with autonomic disorders have equipped clinical practice further with a valuable set of objective tools to assist diagnosis and prognosis. This review, based on current evidence, outlines an international expert consensus set of recommendations to guide clinical electrodiagnostic autonomic testing. Grading and localization of autonomic deficits incorporates scores from sympathetic cardiovascular adrenergic, parasympathetic cardiovagal, and sudomotor testing, as no single test alone is sufficient to diagnose the degree or distribution of autonomic failure. The composite autonomic severity score (CASS) is a useful score of autonomic failure that is normalized for age and gender. Valid indications for autonomic testing include generalized autonomic failure, regional or selective system syndromes of autonomic impairment, peripheral autonomic neuropathy and ganglionopathy, small fiber neuropathy, orthostatic hypotension, orthostatic intolerance, syncope, neurodegenerative disorders, autonomic hyperactivity, and anhidrosis.

MRI Patterns Distinguish AQP4 Antibody Positive Neuromyelitis Optica Spectrum Disorder From Multiple Sclerosis.

Neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS) are inflammatory diseases of the CNS. Overlap in the clinical and MRI features of NMOSD and MS means that distinguishing these conditions can be difficult. With the aim of evaluating the diagnostic utility of MRI features in distinguishing NMOSD from MS, we have conducted a cross-sectional analysis of imaging data and developed predictive models to distinguish the two conditions. NMOSD and MS MRI lesions were identified and defined through a literature search. Aquaporin-4 (AQP4) antibody positive NMOSD cases and age- and sex-matched MS cases were collected. MRI of orbits, brain and spine were reported by at least two blinded reviewers. MRI brain or spine was available for 166/168 (99%) of cases. Longitudinally extensive (OR = 203), "bright spotty" (OR = 93.8), whole (axial; OR = 57.8) or gadolinium (Gd) enhancing (OR = 28.6) spinal cord lesions, bilateral (OR = 31.3) or Gd-enhancing (OR = 15.4) optic nerve lesions, and nucleus tractus solitarius (OR = 19.2), periaqueductal (OR = 16.8) or hypothalamic (OR = 7.2) brain lesions were associated with NMOSD. Ovoid (OR = 0.029), Dawson's fingers (OR = 0.031), pyramidal corpus callosum (OR = 0.058), periventricular (OR = 0.136), temporal lobe (OR = 0.137) and T1 black holes (OR = 0.154) brain lesions were associated with MS. A score-based algorithm and a decision tree determined by machine learning accurately predicted more than 85% of both diagnoses using first available imaging alone. We have confirmed NMOSD and MS specific MRI features and combined these in predictive models that can accurately identify more than 85% of cases as either AQP4 seropositive NMOSD or MS.

Chronic inflammatory demyelinating polyradiculoneuropathy presenting as predominantly sciatic monomelic neuropathy.

BACKGROUND: Chronic inflammatory demyelinating polyneuropathy (CIDP) is a common yet underdiagnosed cause of potentially treatable chronic sensorimotor neuropathy. The classical form of the disease is characterised by symmetrical weakness in both distal and proximal muscle groups accompanied by sensory dysfunction and diminished tendon reflexes lasting more than 2 months. METHOD: The diagnosis of CIDP is supplemented by electrodiagnostic studies and biopsy findings confirming demyelination, in accordance with well-established diagnostic criteria. Atypical presentations of CIDP often pose a diagnostic challenge. RESULTS: In this paper, we present a case of isolated lower limb involvement due to CIDP to raise awareness of this focal lower limb variant. Of particular, significance is the use of lumbosacral plexus MRI to assist in the diagnosis. CONCLUSION: Focal CIDP is an atypical presentation that should be considered in patients presenting with chronic monomelic neuropathy and should be investigated with electrodiagnostic studies, lumbar puncture, nerve biopsy and MRI of the nerve roots and plexuses.

Precision therapy for neuromyelitis optica spectrum disorder: A retrospective analysis of the use of class-switched memory B-cells for individualised rituximab dosing schedules.

BACKGROUND: B-cell depleting treatments are widely used to modify the course of neuromyelitis optica spectrum disorder (NMOSD). Despite recent successful Phase 3 trials of several novel NMOSD therapies, limited availability and high cost constrains their clinical use, and rituximab (RTX) remains a core treatment in many centres. Since 2013, the Royal Prince Alfred Hospital Neuroimmunology Clinic (NIC) has regularly measured class-switched memory B-cells (SMB-cells) in the peripheral blood of patients with NMOSD, who have been treated with RTX, in order to guide retreatment intervals. OBJECTIVE: To assess the management and outcomes of the treated patients, and to determine the effect of SMB-cell monitoring in guiding retreatment intervals. METHODS: A retrospective analysis of hospital records, clinic letters and laboratory data was performed. RESULTS: Sixteen patients with NMOSD received individualised rituximab dosing at NIC between 2013 and 2018. Fourteen (87.5%) were aquaporin-4 antibody (AQP4-Ab) positive; 1 (6.25%) was myelin oligodendrocyte glycoprotein antibody (MOG-Ab) positive and 1 (6.25%) was seronegative. After commencement of RTX, individually dosed according to regular measurements of serum SMB-cells, there was a 77.5% reduction in annualised relapse rate over a mean follow-up time of 46.1 months in our recently active NMOSD patients. Their mean retreatment interval was 50.9 weeks. CONCLUSIONS: This study provides real-world evidence supporting individualised rituximab dosing in the treatment of NMOSD.

Relapse Patterns in NMOSD: Evidence for Earlier Occurrence of Optic Neuritis and Possible Seasonal Variation.

Neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) show overlap in their clinical features. We performed an analysis of relapses with the aim of determining differences between the two conditions. Cases of NMOSD and age- and sex-matched MS controls were collected from across Australia and New Zealand. Demographic and clinical information, including relapse histories, were recorded using a standard questionnaire. There were 75 cases of NMOSD and 101 MS controls. There were 328 relapses in the NMOSD cases and 375 in MS controls. Spinal cord and optic neuritis attacks were the most common relapses in both NMOSD and MS. Optic neuritis (p < 0.001) and area postrema relapses (P = 0.002) were more common in NMOSD and other brainstem attacks were more common in MS (p < 0.001). Prior to age 30 years, attacks of optic neuritis were more common in NMOSD than transverse myelitis. After 30 this pattern was reversed. Relapses in NMOSD were more likely to be treated with acute immunotherapies and were less likely to recover completely. Analysis by month of relapse in NMOSD showed a trend toward reduced risk of relapse in February to April compared to a peak in November to January (P = 0.065). Optic neuritis and transverse myelitis are the most common types of relapse in NMOSD and MS. Optic neuritis tends to occur more frequently in NMOSD prior to the age of 30, with transverse myelitis being more common thereafter. Relapses in NMOSD were more severe. A seasonal bias for relapses in spring-summer may exist in NMOSD.

The clinical profile of NMOSD in Australia and New Zealand.

Neuromyelitis optica spectrum disorders (NMOSD) are an inflammation of the central nervous system associated with autoantibodies to aquaporin-4. We have undertaken a clinic-based survey of NMOSD in the Australia and New Zealand populations with the aim of characterising the clinical features and establishing the value of recently revised diagnostic criteria. Cases of possible NMOSD and age and sex-matched controls with multiple sclerosis (MS) were referred from centres across Australia and New Zealand. Cases were classified as NMOSD if they met the 2015 IPND criteria and remained as suspected NMOSD if they did not. Clinical and paraclinical data were compared across the three groups. NMOSD was confirmed in 75 cases and 89 had suspected NMOSD. There were 101 controls with MS. Age at onset, relapse rates and EDSS scores were significantly higher in NMOSD than in MS. Lesions and symptoms referable to the optic nerve were more common in NMOSD whereas brainstem, cerebellar and cerebral lesions were more common in MS. Longitudinally extensive spinal cord lesions were seen in 48/71 (68%) of cases with NMOSD. Elevations of CSF, white cell count and protein were more common in NMOSD. We have confirmed a clinical pattern of NMOSD that has been seen in several geographical regions. We have demonstrated the clinical utility of the current diagnostic criteria. Distinct patterns of disease are evident in NMOSD and MS, but there remains a large number of patients with NMOSD-like features who do not meet the current diagnostic criteria for NMOSD and remain a diagnostic challenge.

Investigation of tumefactive demyelination is associated with higher economic burden and more adverse events compared with conventional multiple sclerosis.

BACKGROUND: Tumefactive demyelinating lesions occur as part of the spectrum of multiple sclerosis (MS), but can be difficult to distinguish from other large cerebral lesions such as neoplasm or abscess. OBJECTIVES: To estimate the cost associated with diagnostic investigation of patients with tumefactive demyelination (TD), including associated morbidity, and compare this to more typical relapsing-remitting MS. METHODS: Retrospective review of medical records of patients seen between 2013 and 2018 in clinics at the Brain and Mind Centre, Sydney, Australia; a center with tertiary referral expertise in MS. RESULTS: Thirty-one patients with TD and 31 patients with MS were compared. The cost of investigating TD was more than 7.5 times higher per patient than MS ($18,300 vs $2418, p < 0.01). More patients in the TD group were admitted to hospital (22/31 versus 10/31) and ICU admissions only occurred in the TD group (10/22 versus 0/10). Brain biopsy was performed only in the TD group (7 patients), which contributed to cost differences and also accounted for differences in adverse outcomes. CONCLUSION: The cost and morbidity related to investigating TD is higher than in typical MS. Improvements in the diagnosis of TD have the potential to improve health and economic outcomes.

Gain and loss of gastrointestinal symptoms in diabetes mellitus: associations with psychiatric disease, glycemic control, and autonomic neuropathy over 2 years of follow-up.

OBJECTIVE: To prospectively determine the turnover (gain or loss) of gastrointestinal (GI) symptoms in diabetic subjects in relation to glycemic control, autonomic neuropathy and psychiatric disease over a 2-year follow-up. METHODS: Type 1 and type 2 diabetic subjects were recruited from the community, as were community controls. Individual GI symptoms were examined by a validated questionnaire and classified as diarrhea, irritable bowel syndrome, upper GI symptoms, and any GI symptoms at baseline, 12 and 24 months. Glycemic control (glycated hemoglobin), autonomic function (using standardized tests), and psychiatric disease (using the Composite International Diagnostic Interview) were also assessed at these time points. RESULTS: Baseline and 2-year follow-up data were available for 139 diabetic subjects and 55 controls. Glycated hemoglobin at baseline was 7.7% (+/-1.36) in the diabetic group; 5% had severe autonomic dysfunction. There was a significantly higher prevalence of diarrhea in the diabetic subjects. GI symptom turnover varied between 15% and 25% in the diabetic group and was not significantly different from the controls. There was no clear association between turnover of GI symptoms and either glycemic control or autonomic neuropathy. The appearance of depression was associated with gaining of most symptoms apart from irritable bowel syndrome, although the associations did not always reach significance. The univariate results were confirmed after adjusting for age, gender, body mass index, and metformin use. CONCLUSION: The turnover of GI symptoms in diabetic subjects was not associated with glycemic control but there was a positive association with change in depression.

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 ±â€¯1.6% vs healthy controls (HC): -21.8 ±â€¯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 ±â€¯8.1 mm2 vs HC: 9.1 ±â€¯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.

Effective treatment of experimental autoimmune neuritis with Fc fragment of human immunoglobulin.

IV immunoglobulin (IVIg) and its Fc fragment proved effective in preventing further progression of experimental autoimmune neuritis (EAN) in the rat induced by whole bovine peripheral nerve myelin and shortening disease duration. This effectiveness was associated with significant differences in electrophysiological parameters including less prolongation of somatosensory evoked potential (S wave) latencies, better maintained S wave amplitudes, less reduction of distal motor nerve conduction velocity, and better maintained amplitudes of compound muscle action potentials of dorsal foot muscles after stimulation at ankle and hip. Moreover, treatment with IVIg and Fc fragments resulted in less extensive inflammation and demyelination in nerve roots evidenced by significantly lower histological grades. The current study provides direct evidence for the first time that Fc fraction of IVIg is the effective component in the treatment of rat EAN.

Effective treatment of experimental autoimmune neuritis with human immunoglobulin.

High-dose intravenous immunoglobulin (IVIg) is an effective treatment for inflammatory demyelinating neuropathies, although the mechanism(s) of action remain incompletely understood. Experimental autoimmune neuritis (EAN) is an animal model of inflammatory demyelinating neuropathies; however, there have been conflicting reports regarding the efficacy of human IVIg in EAN. To obtain a model suitable for the study of the mechanism(s) of action of IVIg in Guillain-Barré syndrome, we investigated the effect of IVIg in EAN in the rat using clinical, electrophysiological and morphological measures. Human IVIg administered at the onset of signs of disease proved effective in preventing further progression of disease and shortening disease duration. This effectiveness was associated with significant differences in electrophysiological parameters including less prolongation of somatosensory evoked potential (S wave) latencies, better maintained S wave amplitudes, less reduction of distal motor nerve conduction velocity, and better maintained amplitudes of compound muscle action potentials of the dorsal foot muscles after stimulation at ankle and hip. Moreover, treatment with IVIg resulted in significantly lower histological grades in rat EAN. The current study provides evidence that human IVIg is effective in the treatment of EAN in the rat, indicating that this model may facilitate further investigation of the mechanism(s) of action of IVIg in inflammatory demyelinating neuropathies.

Motor unit remodelling in multifocal motor neuropathy: The importance of axonal loss.

OBJECTIVE: To estimate the degree of axonal loss in patients diagnosed with multifocal motor neuropathy (MMN) using a novel assessment of motor unit numbers and size. METHODS: Automated motor unit number estimation using a compound muscle action potential (CMAP) scan was undertaken in median nerves with conduction block. Results were compared with 30 age-matched healthy controls. RESULTS: Compared with healthy controls, MMN patients had fewer motor units (MMN: 33±11vs HC: 93±36 [mean±SD]; p<0.0001) and larger 'size of the largest unit' (MMN: 1.2±0.5mVvs HC: 0.4±0.1mV; p<0.0001), despite having normal distal CMAP amplitudes (MMN: 7.6±1.8mVvs HC: 8.7±2.5mV; p=0.24). CONCLUSIONS: MMN is associated with marked axonal loss which may be masked by striking re-innervation resulting in preservation of distal CMAP amplitudes. SIGNIFICANCE: Assessment of motor unit properties should be incorporated into assessment of disease progression in MMN, given that nerve conduction studies are insensitive to motor unit remodelling.