Assessment of nerve excitability in toxic and metabolic neuropathies

High-dose pharmaceutical-grade biotin in patients with demyelinating neuropathies: a phase 2b open label, uncontrolled, pilot study

BACKGROUND

We proposed to investigate high-dose pharmaceutical-grade biotin in a population of demyelinating neuropathies of different aetiologies, as a proof-of-concept.

METHODS

Phase IIb open label, uncontrolled, single center, pilot study in 15 patients (three groups of five patients) with chronic demyelinating peripheral neuropathy, i.e. chronic inflammatory demyelinating polyradiculoneuropathy, anti-myelin-associated glycoprotein neuropathy and Charcot-Marie-Tooth 1a or 1b. The investigational product was high-dose pharmaceutical-grade biotin (100 mg taken orally three times a day over a maximum of 52 weeks. The primary endpoint was a 10% relative improvement in 2 of the following 4 electrophysiological variables: motor nerve conduction velocity, distal motor latency, F wave latency, duration of the compound muscle action potential. The secondary endpoints included Overall Neuropathy Limitations Scale (ONLS) score, Medical Research Council (MRC) sum score, Inflammatory Neuropathy Cause and Treatment (INCAT) sensory sum score, 10-m walk test, 6-min walk test, posturography parameters, and nerve excitability variables.

RESULTS

The primary endpoint was reached in one patient. In the full population analysis, some secondary endpoints parameters improved: MRC score, INCAT sensory sum score, 6-min walk distance, strength-duration time constant, and rheobase. There was a positive correlation between the improvement in the 6-min walk distance and the strength-duration time constant. Regarding the safety results, 42 adverse events occurred, of which three were of severe intensity but none was considered as related to the investigational product.

CONCLUSIONS

Even if the primary endpoint was not met, administration of high-dose pharmaceutical-grade biotin led to an improvement in various sensory and motor parameters, gait abilities, and nerve excitability parameters. The tolerance of the treatment was satisfactory.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02967679; date 2016/12/05.

Nerve excitability test and lead toxicity: a case-control study

BACKGROUND

Although conventional electrophysiological parameters have been proposed as clinical indicators for monitoring lead neuropathies, their correlations with blood lead level are weak. In this study, we investigated the applicability of nerve excitability tests (NETs) to evaluate lead intoxication.

METHODS

Fourteen workers who were exposed to lead with an elevated blood level ranging from 17.8 to 64.9 µg/dL and 20 healthy controls with similar ages and body heights were enrolled. Both workers and controls underwent nerve conduction studies (NCSs), motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS), and NETs.

RESULTS

NCSs showed prolonged distal latencies and decreased motor nerve conduction velocity of median nerves in the workers but without significant correlation to blood lead level (BLL). Significantly prolonged MEP latency was observed in the workers (+ 6 ms). NETs demonstrated hyperpolarized resting membrane potentials in stimulus-response curves and changes in the property of potassium channels under a hyperpolarized current in threshold electrotonus, implying that lead hyperpolarized nerves by interfering with potassium channels. NETs also showed a better correlation with BLL than conventional electrophysiological parameters.

CONCLUSIONS

Axonal hyperpolarization and central conduction delay are more apparently reflecting elevated BLL than NCS. NET may have the potential for early detection of lead neuropathy.

The threshold tracking nerve conduction study technique: Experience of clinical users unfamiliar with a research-grade neuronal excitability system

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Threshold tracking nerve conduction studies (TTNCSs) measure axon excitability.

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TTNCSs can objectively characterize neuronal dysfunction and treatment response.

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An available research-grade TTNCS system has not been widely implemented .

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Clinical electrophysiologists with varying levels of experience can perform TTNCSs.

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A user-friendly system and education about TTNCSs could broaden use of the technique.

Objective

To 1) explore if clinical electrophysiologists with different degrees of experience performing standard nerve conduction studies could run a threshold tracking nerve conduction study (TTNCS) protocol and 2) learn how clinical users view a research-grade TTNCSs neuronal excitability system.

Methods

Five clinical electrophysiologists conducted a TTNCS session using QTracS and then completed a questionnaire describing their impressions.

Results

All of the electrophysiologists completed the QTracS protocol on an initial attempt. Perceived strengths comprised the ease of preparatory steps and quick protocol speed. Identified drawbacks included an unwieldly user-interface. The electrophysiologists indicated that knowledge of TTNCS principles and applications would be critical for incorporation of the method into clinical use.

Conclusions

This pilot study suggests that clinical electrophysiologists can carry out TTNCSs with a research-grade system. The development of a more user-friendly program, along with dedicated education and training, could lead to wider application of the TTNCS technique.

Significance

Considered together with clinical presentation and other biomarkers, increased use of TTNCSs could provide improved assessment of neuromuscular disease and treatment response.

The Future of Neurotoxicology: A Neuroelectrophysiological Viewpoint

Neuroelectrophysiology is an old science, dating to the 18th century when electrical activity in nerves was discovered. Such discoveries have led to a variety of neurophysiological techniques, ranging from basic neuroscience to clinical applications. These clinical applications allow assessment of complex neurological functions such as (but not limited to) sensory perception (vision, hearing, somatosensory function), and muscle function. The ability to use similar techniques in both humans and animal models increases the ability to perform mechanistic research to investigate neurological problems. Good animal to human homology of many neurophysiological systems facilitates interpretation of data to provide cause-effect linkages to epidemiological findings. Mechanistic cellular research to screen for toxicity often includes gaps between cellular and whole animal/person neurophysiological changes, preventing understanding of the complete function of the nervous system. Building Adverse Outcome Pathways (AOPs) will allow us to begin to identify brain regions, timelines, neurotransmitters, etc. that may be Key Events (KE) in the Adverse Outcomes (AO). This requires an integrated strategy, from in vitro to in vivo (and hypothesis generation, testing, revision). Scientists need to determine intermediate levels of nervous system organization that are related to an AO and work both upstream and downstream using mechanistic approaches. Possibly more than any other organ, the brain will require networks of pathways/AOPs to allow sufficient predictive accuracy. Advancements in neurobiological techniques should be incorporated into these AOP-base neurotoxicological assessments, including interactions between many regions of the brain simultaneously. Coupled with advancements in optogenetic manipulation, complex functions of the nervous system (such as acquisition, attention, sensory perception, etc.) can be examined in real time. The integration of neurophysiological changes with changes in gene/protein expression can begin to provide the mechanistic underpinnings for biological changes. Establishment of linkages between changes in cellular physiology and those at the level of the AO will allow construction of biological pathways (AOPs) and allow development of higher throughput assays to test for changes to critical physiological circuits. To allow mechanistic/predictive toxicology of the nervous system to be protective of human populations, neuroelectrophysiology has a critical role in our future.

Early changes of nerve integrity in preclinical carriers of hereditary transthyretin Ala117Ser amyloidosis with polyneuropathy

BACKGROUND AND PURPOSE

Disease-modifying therapies provide new horizons for hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) to slow neuropathic progression. Initiating treatment at the earliest time requires biomarkers reflecting both small- and large-fiber degeneration in carriers.

METHODS

This study included examinations of pathology (intraepidermal nerve fiber [IENF] density), physiology (nerve conduction studies, autonomic function test, and nerve excitability), and psychophysics (thermal thresholds) in carriers to compare to healthy controls and asymptomatic diabetic patients.

RESULTS

There were 43 carriers (44.2 ± 11.4 years, p.Ala117Ser in 42 carriers), 43 controls (43.4 ± 12.7 years) including 26 noncarrier families, and 50 asymptomatic diabetic patients (58.1 ± 9.5 years). Carriers had lower IENF densities than controls and similar densities as diabetic patients. Median nerve conduction parameters, especially distal motor latency, were the most frequent neurophysiological abnormality in carriers, could differentiate carriers from controls and diabetic patients, were correlated with IENF densities in carriers but not in controls and diabetic patients, and were correlated with nerve excitability parameters in carriers but not in controls. Fifteen carriers (34.9%) with electrophysiological evidence of median nerve entrapment at the wrist had lower IENF densities and more abnormal conduction parameters than carriers without. We defined nerve dysfunction index-the ratio of median distal motor latency to IENF density-which differentiated carriers from controls.

CONCLUSIONS

In late-onset ATTRv-PN carriers with predominant p.Ala117Ser, median conduction parameters were the most common neurophysiological abnormalities and served as surrogate signatures of small- and large-fiber impairment. Combination of median distal motor latency and IENF density can reflect early neuropathy in carriers.

Neuromuscular Electrical Stimulation Reduces Leg Cramps in Patients With Lumbar Degenerative Disorders: A Randomized Placebo-Controlled Trial

Objectives

Lumbar spinal stenosis (LSS) and lumbar disc herniation (LDH) are often accompanied by frequently occurring leg cramps severely affecting patients' life and sleep quality. Recent evidence suggests that neuromuscular electric stimulation (NMES) of cramp‐prone muscles may prevent cramps in lumbar disorders.

Materials and Methods

Thirty‐two men and women (63 ± 9 years) with LSS and/or LDH suffering from cramps were randomly allocated to four different groups. Unilateral stimulation of the gastrocnemius was applied twice a week over four weeks (3 × 6 × 5 sec stimulation trains at 30 Hz above the individual cramp threshold frequency [CTF]). Three groups received either 85%, 55%, or 25% of their maximum tolerated stimulation intensity, whereas one group only received pseudo‐stimulation.

Results

The number of reported leg cramps decreased in the 25% (25 ± 14 to 7 ± 4; p = 0.002), 55% (24 ± 10 to 10 ± 11; p = 0.014) and 85%NMES (23 ± 17 to 1 ± 1; p < 0.001) group, whereas it remained unchanged after pseudo‐stimulation (20 ± 32 to 19 ± 33; p > 0.999). In the 25% and 85%NMES group, this improvement was accompanied by an increased CTF (p < 0.001).

Conclusion

Regularly applied NMES of the calf muscles reduces leg cramps in patients with LSS/LDH even at low stimulation intensity.

Immune-mediated axonal dysfunction in seropositive and seronegative primary Sjögren's syndrome

OBJECTIVE

The present study investigates the peripheral neuropathy in Primary Sjögren's syndrome (pSS) using the nerve excitability test to further elucidate how peripheral nerves are affected by the autoantibodies.

METHODS

Each patient received clinical evaluation, examination for anti-SSA/Ro and anti-SSB/La antibodies titer, paired motor and sensory nerve excitability test, thermal quantitative sensory test (QST), and nerve conduction study (NCS).

RESULTS

A total of 40 pSS patients wasenrolled. Motor axonal study of the pSS with positive anti-SSA/Ro or anti-SSB/La antibodies (n = 28) was found to have increased stimulus for 50% compound muscle action potential (CMAP) (P < 0.05), increased rheobase (P < 0.01), increased minimum I/V slope (P < 0.01) and hyperpolarizing I/V slope (P < 0.05), increased relative refractory period (RRP, P < 0.001), decreased accommodation of threshold electrotonus toward depolarizing current (P < 0.05), and increased accommodation toward hyperpolarizing current (P < 0.05). Seronegative pSS (n = 10) showed much less prominent motor axonal changes, showing only increased minimum I/V slope (P < 0.05). Sensory axonal study in seropositive pSS patients is found to have increased stimulus for 50% sensory nerve action potential (SNAP) (P < 0.01), decreased latency (P < 0.01), increased RRP (P < 0.01), and increased subexcitability (P < 0.05). Seronegative pSS patients have shown no significant sensory axonal changes. Thermal QST showed more prominent abnormalities in seronegative pSS compared to seropositive pSS.

INTERPRETATION

Anti-SSA/Ro and anti-SSB/La autoantibodies might cause dysfunction in nodal and internodal region of the axon and small nerve fibers; meanwhile, autoreactive antibodies in seronegative pSS mainly affect small nerve fibers. Thus, the underlying pathophysiology for the two types of pSS is different.

Methods for in vivo studies in rodents of chemotherapy induced peripheral neuropathy

Peripheral neuropathy is one of the most common, dose limiting, and long-lasting disabling adverse events of chemotherapy treatment. Unfortunately, no treatment has proven efficacy to prevent this adverse effect in patients or improve the nerve regeneration, once it is established. Experimental models, particularly using rats and mice, are useful to investigate the mechanisms related to axonal or neuronal degeneration and target loss of function induced by neurotoxic drugs, as well as to test new strategies to prevent the development of neuropathy and to improve functional restitution. Therefore, objective and reliable methods should be applied for the assessment of function and innervation in adequately designed in vivo studies of CIPN, taking into account the impact of age, sex and species/strains features. This review gives an overview of the most useful methods to assess sensory, motor and autonomic functions, electrophysiological and morphological tests in rodent models of peripheral neuropathy, focused on CIPN. We include as well a proposal of protocols that may improve the quality and comparability of studies undertaken in different laboratories. It is recommended to apply more than one functional method for each type of function, and to perform parallel morphological studies in the same targets and models.

Early sensory neurophysiological changes in prediabetes

AIMS/INTRODUCTION

To elucidate whether axonal changes arise in the prediabetic state and to find a biomarker for early detection of neurophysiological changes.

MATERIALS AND METHODS

We enrolled asymptomatic diabetes patients, as well as prediabetic and normoglycemic individuals to test sensory nerve excitability, and we analyzed those findings and their correlation with clinical profiles.

RESULTS

In nerve excitability tests, superexcitability in the recovery cycle showed increasing changes in the normoglycemic, prediabetes and diabetes cohorts (-19.09 ± 4.56% in normoglycemia, -22.39 ± 3.16% in prediabetes and -23.71 ± 5.15% in diabetes, P = 0.002). Relatively prolonged distal sensory latency was observed in the median nerve (3.12 ± 0.29 ms in normoglycemia, 3.23 ± 0.38 ms in prediabetes and 3.45 ± 0.43 ms in diabetes, P = 0.019). Superexcitability was positively correlated with fasting plasma glucose (r = 0.291, P = 0.009) and glycated hemoglobin (r = 0.331, P = 0.003) in all participants.

CONCLUSIONS

Sensory superexcitability and latencies are the most sensitive parameters for detecting preclinical physiological dysfunction in prediabetes. In addition, changes in favor of superexcitability were positively correlated with glycated hemoglobin for all participants. These results suggest that early axonal changes start in the prediabetic stage, and that the monitoring strategy for polyneuropathy should start as early as prediabetes.

Essential References for Structural Analysis of the Peripheral Nervous System for Pathologists and Toxicologists

Toxicologic neuropathology for the peripheral nervous system (PNS) is a vital but often underappreciated element of basic translational research and safety assessment. Evaluation of the PNS may be complicated by unfamiliarity with normal nerve and ganglion biology, which differs to some degree among species; the presence of confounding artifacts related to suboptimal sampling and processing; and limited experience with differentiating such artifacts from genuine disease manifestations and incidental background changes. This compilation of key PNS neurobiology, neuropathology, and neurotoxicology references is designed to allow pathologists and toxicologists to readily access essential information that is needed to enhance their proficiency in evaluating and interpreting toxic changes in PNS tissues from many species.

Muscle weakness: Understanding the principles of myopathy and neuropathy in the critically ill patient and the management options

Myo-neuropathy of the critically ill patient is a difficult nosological entity to understand and manage. It appears soon after injury, and it is estimated that 20-30% of patients admitted to Intensive Care Units will develop it in some degree. Although muscular and nervous involvement are related, the former has a better prognosis. Myo-neuropathy associates to more morbidity, longer stay in Intensive Care Unit and in hospital, and also to higher costs and mortality. It is considered part of the main determinants of the new entities: the Chronic Critical Patient and the Post Intensive Care Syndrome. This update focuses on aetiology, pathophysiology, diagnosis and strategies that can prevent, alleviate and/or improve muscle (or muscle-nerve) weakness.

Synthetic Pinnatoxins A and G Reversibly Block Mouse Skeletal Neuromuscular Transmission In Vivo and In Vitro

Pinnatoxins (PnTXs) A-H constitute an emerging family belonging to the cyclic imine group of phycotoxins. Interest has been focused on these fast-acting and highly-potent toxins because they are widely found in contaminated shellfish. Despite their highly complex molecular structure, PnTXs have been chemically synthetized and demonstrated to act on various nicotinic acetylcholine receptor (nAChR) subtypes. In the present work, PnTX-A, PnTX-G and analogue, obtained by chemical synthesis with a high degree of purity (>98%), have been studied in vivo and in vitro on adult mouse and isolated nerve-muscle preparations expressing the mature muscle-type (α1)₂β1δε nAChR. The results show that PnTX-A and G acted on the neuromuscular system of anesthetized mice and blocked the compound muscle action potential (CMAP) in a dose- and time-dependent manner, using a minimally invasive electrophysiological method. The CMAP block produced by both toxins in vivo was reversible within 6–8 h. PnTX-A and G, applied to isolated extensor digitorum longus nerve-muscle preparations, blocked reversibly isometric twitches evoked by nerve stimulation. The action of PnTX-A was reversed by 3,4-diaminopyridine. Both toxins exerted no direct action on muscle fibers, as revealed by direct muscle stimulation. PnTX-A and G blocked synaptic transmission at mouse neuromuscular junctions and PnTX-A amino ketone analogue (containing an open form of the imine ring) had no effect on neuromuscular transmission. These results indicate the importance of the cyclic imine for interacting with the adult mammalian muscle-type nAChR. Modeling and docking studies revealed molecular determinants responsible for the interaction of PnTXs with the muscle-type nAChR.

From identification to functional characterization of cyriotoxin-1a, an antinociceptive toxin from the spider Cyriopagopus schioedtei

BACKGROUND AND PURPOSE

The Na_V 1.7 channel is highly expressed in dorsal root ganglia of the sensory nervous system and plays a central role in the pain signalling process. We investigated a library prepared from original venoms of 117 different animals to identify new selective inhibitors of this target.

EXPERIMENTAL APPROACH

We used high throughput screening of a large venom collection using automated patch-clamp experiments on human voltage-gated sodium channel subtypes and then in vitro and in vivo electrophysiological experiments to characterize the active peptides that have been purified, sequenced, and chemically synthesized. Analgesic effects were evaluated in vivo in mice models.

KEY RESULTS

We identified cyriotoxin-1a (CyrTx-1a), a novel peptide isolated from Cyriopagopus schioedtei spider venom, as a candidate for further characterization. This 33 amino acids toxin belongs to the inhibitor cystine knot structural family and inhibits hNa_V 1.1-1.3 and 1.6-1.7 channels in the low nanomolar range, compared to the micromolar range for hNa_V 1.4-1.5 and 1.8 channels. CyrTx-1a was 920 times more efficient at inhibiting tetrodotoxin (TTX)-sensitive than TTX-resistant sodium currents recorded from adult mouse dorsal root ganglia neurons and in vivo electrophysiological experiments showed that CyrTx-1a was approximately 170 times less efficient than huwentoxin-IV at altering mouse skeletal neuromuscular excitability properties. CyrTx-1a exhibited an analgesic effect in mice by increasing reaction time in the hot-plate assay.

CONCLUSIONS AND IMPLICATIONS

The pharmacological profile of CyrTx-1a paves the way for further molecular engineering aimed to optimize the potential antinociceptive properties of this peptide.

Preventive action of benztropine on platinum-induced peripheral neuropathies and tumor growth

The endogenous cholinergic system plays a key role in neuronal cells, by suppressing neurite outgrowth and myelination and, in some cancer cells, favoring tumor growth. Platinum compounds are widely used as part of first line conventional cancer chemotherapy; their efficacy is however limited by peripheral neuropathy as a major side-effect. In a multiple sclerosis mouse model, benztropine, that also acts as an anti-histamine and a dopamine re-uptake inhibitor, induced the differentiation of oligodendrocytes through M1 and M3 muscarinic receptors and enhanced re-myelination. We have evaluated whether benztropine can increase anti-tumoral efficacy of oxaliplatin, while preventing its neurotoxicity.We showed that benztropine improves acute and chronic clinical symptoms of oxaliplatin-induced peripheral neuropathies in mice. Sensory alterations detected by electrophysiology in oxaliplatin-treated mice were consistent with a decreased nerve conduction velocity and membrane hyperexcitability due to alterations in the density and/or functioning of both sodium and potassium channels, confirmed by action potential analysis from ex-vivo cultures of mouse dorsal root ganglion sensory neurons using whole-cell patch-clamp. These alterations were all prevented by benztropine. In oxaliplatin-treated mice, MBP expression, confocal and electronic microscopy of the sciatic nerves revealed a demyelination and confirmed the alteration of the myelinated axons morphology when compared to animals injected with oxaliplatin plus benztropine. Benztropine also prevented the decrease in neuronal density in the paws of mice injected with oxaliplatin. The neuroprotection conferred by benztropine against chemotherapeutic drugs was associated with a lower expression of inflammatory cytokines and extended to diabetic-induced peripheral neuropathy in mice.Mice receiving benztropine alone presented a lower tumor growth when compared to untreated animals and synergized the anti-tumoral effect of oxaliplatin, a phenomenon explained at least in part by benztropine-induced ROS imbalance in tumor cells.This report shows that blocking muscarinic receptors with benztropine prevents peripheral neuropathies and increases the therapeutic index of oxaliplatin. These results can be rapidly transposable to patients as benztropine is currently indicated in Parkinson's disease in the United States.

Trends and Cost Analysis of Upper Extremity Nerve Injury Using the National (Nationwide) Inpatient Sample

OBJECTIVE

Epidemiology in upper extremity peripheral nerve injury (PNI) has not been comprehensively evaluated. The aim of this study was to calculate updated incidence of upper extremity PNIs in the United States and examine clinical trends and costs using a national database.

METHODS

The National (Nationwide) Inpatient Sample was used to evaluate patients with upper extremity PNI (International Classification of Diseases, Ninth Revision, Clinical Modification 9534, 9550-9559) in 2001-2013.

RESULTS

A weighted total of 170,579 patients experienced upper extremity PNI, representing a mean incidence of 43.8/1 million people annually. Mean (± SEM) age of patients was 38.1 ± 0.05 years, 74.3% of patients were male, and 49.0% were Caucasian. PNIs occurred to the ulnar (17.8%), radial (15.1%), digital (18.0%), median (13.0%), multiple (11.5%), and other (10.1%) nerves and brachial plexus (14.5%). The number of upper extremity PNIs decreased overall. Average care charge was $47,004 ± $185, with an average increase of $4623/year and compound annual growth rate of 9.59%. Although surgical nerve repair and home disposition were common with isolated PNIs, patients with brachial plexus PNIs did not have nerve surgery and were more likely to be discharged to skilled nursing facilities. Multivariate analysis showed that length of stay (β = 0.677, P = 0.0001) and number of procedures (β = 0.188, P = 0.0001) most affected total patient charges.

CONCLUSIONS

These results suggest an overall decrease in number of PNIs, suggesting lower incidence or frequency of detection; however, the cost of care has increased. Despite advances in nerve repair techniques, nerve surgery rates have not increased, especially for brachial plexus injuries, which may be undertreated.

Correlation between markers of peripheral nerve function and structure in type 1 diabetes

BACKGROUND

Clinical and experimental studies in patients with type 1 and type 2 diabetes have demonstrated changes in ion channel function and nerve structure. In this study, we investigated the relationship between axonal dysfunction and morphological change in diabetic polyneuropathy by using neuromuscular ultrasound and nerve excitability techniques. We also explored possible differences in this relationship between type 1 and type 2 diabetes.

METHODS

Nerve ultrasound and corresponding motor excitability studies were undertaken in 110 diabetes patients (50 type 1; 60 type 2) and 60 age-matched controls (30 for each group). Neuropathy severity was assessed by using total neuropathy score. Median and tibial nerve cross-sectional areas were measured at nonentrapment sites by using high-resolution linear probe.

RESULTS

Median and tibial nerve cross-sectional areas were significantly higher in diabetes patients compared with controls: type 1 (median = 7.6 ± 0.2 mm² vs 6.3 ± 0.1 mm² ; tibial = 14.5 ± 0.7 mm² vs 10.8 ± 0.3 mm² , P < .05) and type 2 (median = 9.1 ± 0.3 mm² vs 7.2 ± 0.1 mm² ; tibial = 18.5 ± 1.0 mm² vs 12.8 ± 0.5 mm² , P < .05). In the type 1 cohort, significant correlations were found between nerve cross-sectional area and excitability parameters including resting current-threshold slope (median: r = 0.523, P < .0001; tibial: r = -0.571, P = .004) and depolarizing threshold electrotonus at 90 to 100 ms (median: 0.424, P < .01; tibial: r = 0.435, P = .030). In contrast, there was no relationship between excitability values and nerve cross-sectional area in the type 2 cohort.

CONCLUSIONS

This study has identified correlation between markers of axonal membrane function and structural abnormalities in peripheral nerves of type 1 diabetes patients. The differential relationship in nerve function and structure between type 1 and type 2 diabetes provides clinical evidence that different pathophysiological mechanisms underlie the development of neuropathy in these patient groups.

Muscular cramp: causes and management

Muscular cramp is a common symptom in healthy people, especially among the elderly and in young people after vigorous or peak exercise. It is prominent in a number of benign neurological syndromes. It is a particular feature of chronic neurogenic disorders, especially amyotrophic lateral sclerosis. A literature review was undertaken to understand the diverse clinical associations of cramp and its neurophysiological basis, taking into account recent developments in membrane physiology and modulation of motor neuronal excitability. Many aspects of cramping remain incompletely understood and require further study. Current treatment options are correspondingly limited.

Direct evidence for high affinity blockade of NaV1.6 channel subtype by huwentoxin-IV spider peptide, using multiscale functional approaches

The Chinese bird spider huwentoxin-IV (HwTx-IV) is well-known to be a highly potent blocker of Na_V1.7 subtype of voltage-gated sodium (Na_V) channels, a genetically validated analgesic target, and thus promising as a potential lead molecule for the development of novel pain therapeutics. In the present study, the interaction between HwTx-IV and Na_V1.6 channel subtype was investigated using multiscale (from in vivo to individual cell) functional approaches. HwTx-IV was approximatively 2 times more efficient than tetrodotoxin (TTX) to inhibit the compound muscle action potential recorded from the mouse skeletal neuromuscular system in vivo, and 30 times more effective to inhibit nerve-evoked than directly-elicited muscle contractile force of isolated mouse hemidiaphragms. These results strongly suggest that the inhibition of nerve-evoked skeletal muscle functioning, produced by HwTx-IV, resulted from a toxin-induced preferential blockade of Na_V1.6, compared to Na_V1.4, channel subtype. This was confirmed by whole-cell automated patch-clamp experiments performed on human embryonic kidney (HEK)-293 cells overexpressing hNa_V1.1-1.8 channel subtypes. HwTx-IV was also approximatively 850 times more efficient to inhibit TTX-sensitive than TTX-resistant sodium currents recorded from mouse dorsal root ganglia neurons. Finally, based on our data, we predict that blockade of the Na_V1.6 channel subtype was involved in the in vivo toxicity of HwTx-IV, although this toxicity was more than 2 times lower than that of TTX. In conclusion, our results provide detailed information regarding the effects of HwTx-IV and allow a better understanding of the side-effect mechanisms involved in vivo and of channel subtype interactions resulting from the toxin activity.

Selective recurrent laryngeal nerve stimulation using a penetrating electrode array in the feline model

OBJECTIVES/HYPOTHESIS

Laryngeal muscles (LMs) are controlled by the recurrent laryngeal nerve (RLN), injury of which can result in vocal fold (VF) paralysis (VFP). We aimed to introduce a bioelectric approach to selective stimulation of LMs and graded muscle contraction responses.

STUDY DESIGN

Acute experiments in cats.

METHODS

The study included six anesthetized cats. In four cats, a multichannel penetrating microelectrode array (MEA) was placed into an uninjured RLN. For RLN injury experiments, one cat received a standardized hemostat-crush injury, and one cat received a transection-reapproximation injury 4 months prior to testing. In each experiment, three LMs (thyroarytenoid, posterior cricoarytenoid, and cricothyroid muscles) were monitored with an electromyographic (EMG) nerve integrity monitoring system. Electrical current pulses were delivered to each stimulating channel individually. Elicited EMG voltage outputs were recorded for each muscle. Direct videolaryngoscopy was performed for visualization of VF movement.

RESULTS

Stimulation through individual channels led to selective activation of restricted nerve populations, resulting in selective contraction of individual LMs. Increasing current levels resulted in rising EMG voltage responses. Typically, activation of individual muscles was successfully achieved via single placement of the MEA by selection of appropriate stimulation channels. VF abduction was predominantly observed on videolaryngoscopy. Nerve histology confirmed injury in cases of RLN crush and transection experiments.

CONCLUSIONS

We demonstrated the ability of a penetrating MEA to selectively stimulate restricted fiber populations within the feline RLN and selectively elicit contractions of discrete LMs in both acute and injury-model experiments, suggesting a potential role for intraneural MEA implantation in VFP management.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:1606-1614, 2018.

In vivo assessment of neurological channelopathies: Application of peripheral nerve excitability studies

With the rapid evolution of understanding of neurological channelopathies comes a need for sensitive tools to evaluate patients in clinical practice. Neurological channelopathies with a single-gene basis can manifest as seizures, headache, ataxia, vertigo, confusion, weakness and neuropathic pain and it is likely that other genetic factors contribute to the phenotype of many of these disorders. Ion channel dysfunction can result in abnormal cell membrane excitability but utilisation of advanced neurophysiology techniques has lagged behind developments in clinical, genetic and imaging evaluation of channelopathies. However, momentum in the application of in vivo axonal excitability testing sees these tests emerging as valuable tools, with the capacity to provide sensitive and specific insights into the mechanism of disease. While single-channel function cannot be directly measured in vivo, evaluation of subjects with single-gene channelopathies has provided insights into the effects of mutation-related alterations of membrane excitability, as well as compensatory adaptive changes. By showing how ion channel dysfunction can affect axonal excitability in vivo, studies of the excitability of peripheral nerve axons complement in vitro analysis of single channel activity. The interpretation of results is enhanced by mathematical modelling of axonal function and insights provided by in vitro work. This article is part of the Special Issue entitled 'Channelopathies.'

Uncovering sensory axonal dysfunction in asymptomatic type 2 diabetic neuropathy

This study investigated sensory and motor nerve excitability properties to elucidate the development of diabetic neuropathy. A total of 109 type 2 diabetes patients were recruited, and 106 were analyzed. According to neuropathy severity, patients were categorized into G0, G1, and G2+3 groups using the total neuropathy score-reduced (TNSr). Patients in the G0 group were asymptomatic and had a TNSr score of 0. Sensory and motor nerve excitability data from diabetic patients were compared with data from 33 healthy controls. Clinical assessment, nerve conduction studies, and sensory and motor nerve excitability testing data were analyzed to determine axonal dysfunction in diabetic neuropathy. In the G0 group, sensory excitability testing revealed increased stimulus for the 50% sensory nerve action potential (P<0.05), shortened strength-duration time constant (P<0.01), increased superexcitability (P<0.01), decreased subexcitability (P<0.05), decreased accommodation to depolarizing current (P<0.01), and a trend of decreased accommodation to hyperpolarizing current in threshold electrotonus. All the changes progressed into G1 (TNSr 1–8) and G2+3 (TNSr 9–24) groups. In contrast, motor excitability only had significantly increased stimulus for the 50% compound motor nerve action potential (P<0.01) in the G0 group. This study revealed that the development of axonal dysfunction in sensory axons occurred prior to and in a different fashion from motor axons. Additionally, sensory nerve excitability tests can detect axonal dysfunction even in asymptomatic patients. These insights further our understanding of diabetic neuropathy and enable the early detection of sensory axonal abnormalities, which may provide a basis for neuroprotective therapeutic approaches.

Niclosamide Inhibits Oxaliplatin Neurotoxicity while Improving Colorectal Cancer Therapeutic Response

Neuropathic pain is a limiting factor of platinum-based chemotherapies. We sought to investigate the neuroprotective potential of niclosamide in peripheral neuropathies induced by oxaliplatin. Normal neuron-like and cancer cells were treated in vitro with oxaliplatin associated or not with an inhibitor of STAT3 and NF-κB, niclosamide. Cell production of reactive oxygen species and viability were measured by 2',7'-dichlorodihydrofluorescein diacetate and crystal violet. Peripheral neuropathies were induced in mice by oxaliplatin with or without niclosamide. Neurologic functions were assessed by behavioral and electrophysiologic tests, intraepidermal innervation, and myelination by immunohistochemical, histologic, and morphologic studies using confocal microscopy. Efficacy on tumor growth was assessed in mice grafted with CT26 colon cancer cells. In neuron-like cells, niclosamide downregulated the production of oxaliplatin-mediated H₂O₂, thereby preventing cell death. In colon cancer cells, niclosamide enhanced oxaliplatin-mediated cell death through increased H₂O₂ production. These observations were explained by inherent lower basal levels of GSH in cancer cells compared with normal and neuron-like cells. In neuropathic mice, niclosamide prevented tactile hypoesthesia and thermal hyperalgesia and abrogated membrane hyperexcitability. The teniacide also prevented intraepidermal nerve fiber density reduction and demyelination in oxaliplatin mice in this mixed form of peripheral neuropathy. Niclosamide prevents oxaliplatin-induced increased levels of IL6, TNFα, and advanced oxidized protein products. Niclosamide displayed antitumor effects while not abrogating oxaliplatin efficacy. These results indicate that niclosamide exerts its neuroprotection both in vitro and in vivo by limiting oxaliplatin-induced oxidative stress and neuroinflammation. These findings identify niclosamide as a promising therapeutic adjunct to oxaliplatin chemotherapy. Mol Cancer Ther; 16(2); 300-11. ©2016 AACR.

Comparative study to evaluate the effects of peritoneal and hemodialysis on peripheral nerve function

INTRODUCTION

There is no specific treatment for neuropathy in chronic kidney disease (CKD). We compared nerve function across hemodialysis (HD) and peritoneal dialysis (PD).

METHODS

Subjects underwent neurological assessment and neurophysiological testing using nerve excitability studies. Pre- and postdialysis studies were undertaken in HD (n = 10) and PD (n = 10) patients and were compared with stage 4 CKD patients (n = 12) and healthy controls (n = 20).

RESULTS

There were prominent differences in nerve excitability between the groups (P <  0.001). The HD group was significantly abnormal compared with all groups for excitability parameters, while the PD group demonstrated results similar to the CKD group. Pre- and postdialysis fluctuations were pronounced in the HD group, while the PD group showed less severe fluctuations.

CONCLUSIONS

PD patients demonstrated greater normality of nerve excitability compared with the HD group despite similar duration of dialysis. These results suggest PD may provide greater homeostatic stability and may be neurologically beneficial. Muscle Nerve 54: 58-64, 2016.

Short-term peripheral nerve stimulation ameliorates axonal dysfunction after spinal cord injury

There is accumulating evidence that peripheral motor axons deteriorate following spinal cord injury (SCI). Secondary axonal dysfunction can exacerbate muscle atrophy, contribute to peripheral neuropathies and neuropathic pain, and lead to further functional impairment. In an attempt to ameliorate the adverse downstream effects that developed following SCI, we investigated the effects of a short-term peripheral nerve stimulation (PNS) program on motor axonal excitability in 22 SCI patients. Axonal excitability studies were undertaken in the median and common peroneal nerves (CPN) bilaterally before and after a 6-wk unilateral PNS program. PNS was delivered percutaneously over the median nerve at the wrist and CPN around the fibular head, and the compound muscle action potential (CMAP) from the abductor pollicis brevis and tibialis anterior was recorded. Stimulus intensity was above motor threshold, and pulses (450 μs) were delivered at 100 Hz with a 2-s on/off cycle for 30 min 5 days/wk. SCI patients had consistently high thresholds with a reduced CMAP consistent with axonal loss; in some patients the peripheral nerves were completely inexcitable. Nerve excitability studies revealed profound changes in membrane potential, with a "fanned-in" appearance in threshold electrotonus, consistent with membrane depolarization, and significantly reduced superexcitability during the recovery cycle. These membrane dysfunctions were ameliorated after 6 wk of PNS, which produced a significant hyperpolarizing effect. The contralateral, nonstimulated nerves remained depolarized. Short-term PNS reversed axonal dysfunction following SCI, may provide an opportunity to prevent chronic changes in axonal and muscular function, and may improve rehabilitation outcomes.

Peripheral nerve axonal excitability studies: expanding the neurophysiologist's armamentarium

Nerve excitability studies have emerged as a recent novel non-invasive technique that offers complementary information to that provided by more conventional nerve conduction studies, the latter which provide only limited indices of peripheral nerve function. Such novel tools allow for the assessment of peripheral axonal biophysical properties that include ion channels, energy-dependent pumps and membrane potential in health and disease. With improvements in technique and development of protocols, a typical study can be completed in a short period of time and rapid measurement of multiple excitability indices can be achieved that provide insight into different aspects of peripheral nerve function. The advent of automated protocols for the assessment of nerve excitability has promoted their use in previous studies investigating disease pathophysiology such as in metabolic, toxic and demyelinating neuropathies, amyotrophic lateral sclerosis, stroke, spinal cord injury and inherited channelopathies. In more recent years, the use of nerve excitability studies have additionally provided insights into the pathophysiological mechanisms underlying cerebellar disorders that include stroke and familial cerebellar ataxias such as episodic ataxia types 1 and 2. Moreover, this technique may have diagnostic and therapeutic implications that may encompass a broader range of neurodegenerative cerebellar ataxias in years to come. In the foreseeable future, this technique may eventually be incorporated into clinical practice expanding the currently available armamentarium to the neurophysiologist.

Arginine butyrate per os protects mdx mice against cardiomyopathy, kyphosis and changes in axonal excitability

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease caused by lack of dystrophin, a sub-sarcolemmal protein, which leads to dramatic muscle deterioration. We studied in mdx mice, the effects of oral administration of arginine butyrate (AB), a compound currently used for the treatment of sickle cell anemia in children, on cardiomyopathy, vertebral column deformation and electromyographic abnormalities. Monthly follow-up by echocardiography from the 8th month to the 14th month showed that AB treatment protected the mdx mice against drastic reduction (20-23%) of ejection fraction and fractional shortening, and also against the ≈20% ventricular dilatation and 25% cardiac hypertrophy observed in saline-treated mdx mice. The phenotypic improvement was corroborated by the decrease in serum CK level and by better fatigue resistance. Moreover, AB treatment protected against the progressive spinal deformity observed in mdx mice, another similarity with DMD patients. The value of the kyphosis index in AB-treated mice reached 94% of the value in C57BL/10 mice. Finally, axonal excitability parameters such as the membrane resting potential, the threshold and amplitude of the action potential, the absolute and relative refractory periods and the supernormal and subnormal periods, recorded from caudal and plantar muscles in response to excitability tests, that were modified in saline-treated mdx mice were not significantly changed, compared with wild-type animals, in AB-treated mdx mice. All of these results suggest that AB could be a potential treatment for DMD patients.

Treatment of oxaliplatin-induced peripheral neuropathy by intravenous mangafodipir

BACKGROUND

The majority of patients receiving the platinum-based chemotherapy drug oxaliplatin develop peripheral neurotoxicity. Because this neurotoxicity involves ROS production, we investigated the efficacy of mangafodipir, a molecule that has antioxidant properties and is approved for use as an MRI contrast enhancer.

METHODS

The effects of mangafodipir were examined in mice following treatment with oxaliplatin. Neurotoxicity, axon myelination, and advanced oxidized protein products (AOPPs) were monitored. In addition, we enrolled 23 cancer patients with grade ≥ 2 oxaliplatin-induced neuropathy in a phase II study, with 22 patients receiving i.v. mangafodipir following oxaliplatin. Neuropathic effects were monitored for up to 8 cycles of oxaliplatin and mangafodipir.

RESULTS

Mangafodipir prevented motor and sensory dysfunction and demyelinating lesion formation. In mice, serum AOPPs decreased after 4 weeks of mangafodipir treatment. In 77% of patients treated with oxaliplatin and mangafodipir, neuropathy improved or stabilized after 4 cycles. After 8 cycles, neurotoxicity was downgraded to grade ≥ 2 in 6 of 7 patients. Prior to enrollment, patients received an average of 880 ± 239 mg/m2 oxaliplatin. Patients treated with mangafodipir tolerated an additional dose of 458 ± 207 mg/m2 oxaliplatin despite preexisting neuropathy. Mangafodipir responders managed a cumulative dose of 1,426 ± 204 mg/m2 oxaliplatin. Serum AOPPs were lower in responders compared with those in nonresponders.

CONCLUSION

Our study suggests that mangafodipir can prevent and/or relieve oxaliplatin-induced neuropathy in cancer patients. Trial registration. Clinicaltrials.gov NCT00727922. Funding. Université Paris Descartes, Ministère de la Recherche et de l'Enseignement Supérieur, and Assistance Publique-Hôpitaux de Paris.

Toxic c17-sphinganine analogue mycotoxin, contaminating tunisian mussels, causes flaccid paralysis in rodents

Severe toxicity was detected in mussels from Bizerte Lagoon (Northern Tunisia) using routine mouse bioassays for detecting diarrheic and paralytic toxins not associated to classical phytoplankton blooming. The atypical toxicity was characterized by rapid mouse death. The aim of the present work was to understand the basis of such toxicity. Bioassay-guided chromatographic separation and mass spectrometry were used to detect and characterize the fraction responsible for mussels’ toxicity. Only a C17-sphinganine analog mycotoxin (C17-SAMT), with a molecular mass of 287.289 Da, was found in contaminated shellfish. The doses of C17-SAMT that were lethal to 50% of mice were 750 and 150 μg/kg following intraperitoneal and intracerebroventricular injections, respectively, and 900 μg/kg following oral administration. The macroscopic general aspect of cultures and the morphological characteristics of the strains isolated from mussels revealed that the toxicity episodes were associated to the presence of marine microfungi (Fusarium sp., Aspergillus sp. and Trichoderma sp.) in contaminated samples. The major in vivo effect of C17-SAMT on the mouse neuromuscular system was a dose- and time-dependent decrease of compound muscle action potential amplitude and an increased excitability threshold. In vitro, C17-SAMT caused a dose- and time-dependent block of directly- and indirectly-elicited isometric contraction of isolated mouse hemidiaphragms.

Association between calcineurin inhibitor treatment and peripheral nerve dysfunction in renal transplant recipients

Neurotoxicity is a significant clinical side effect of immunosuppressive treatment used in prophylaxis for rejection in solid organ transplants. This study aimed to provide insights into the mechanisms underlying neurotoxicity in patients receiving immunosuppressive treatment following renal transplantation. Clinical and neurophysiological assessments were undertaken in 38 patients receiving immunosuppression following renal transplantation, 19 receiving calcineurin inhibitor (CNI) therapy and 19 receiving a calcineurin-free (CNI-free) regimen. Groups were matched for age, gender, time since transplant and renal function and compared to normal controls (n = 20). The CNI group demonstrated marked differences in nerve excitability parameters, suggestive of nerve membrane depolarization (p < 0.05). Importantly, there were no differences between the two CNIs (cyclosporine A or tacrolimus). In contrast, CNI-free patients showed no differences to normal controls. The CNI-treated patients had a higher prevalence of clinical neuropathy and higher neuropathy severity scores. Longitudinal studies were undertaken in a cohort of subjects within 12 months of transplantation (n = 10). These studies demonstrated persistence of abnormalities in patients maintained on CNI-treatment and improvement noted in those who were switched to a CNI-free regimen. The results of this study have significant implications for selection, or continuation, of immunosuppressive therapy in renal transplant recipients, especially those with pre-existing neurological disability.

Evidence for a causal relationship between hyperkalaemia and axonal dysfunction in end-stage kidney disease

OBJECTIVE

Potassium (K(+)) has been implicated as a factor in the development of uraemic neuropathy. This study was undertaken to investigate whether hyperkalaemia plays a causal role in axonal dysfunction in end-stage kidney disease (ESKD).

METHODS

Median motor nerve excitability studies were undertaken in four haemodialysis patients during a modified dialysis session. The serum K(+) level was "clamped" (fixed) for the first 3h of dialysis, whilst allowing all other solutes to be removed, this was followed by dialysis against low dialysate K(+) for a further 4 h. Blood chemistry and nerve excitability studies were undertaken prior to, during and following dialysis. Results were compared to results from the same patients during routine dialysis sessions.

RESULTS

All patients demonstrated significant nerve excitability abnormalities reflective of nerve membrane depolarization in pre-dialysis recordings (p<0.01). After the 3 h clamp period, serum K(+) remained elevated (5.0 mmol/L) and nerve excitability remained highly abnormal, despite the significant clearance of other uraemic toxins. In contrast, studies undertaken during routine dialysis sessions demonstrated significant improvement in both serum K(+) and nerve function after 3 h.

CONCLUSIONS

The current study has established a causal relationship between serum K(+) and axonal membrane depolarization in haemodialysis patients.

SIGNIFICANCE

From a clinical perspective, strict K(+) control may help improve nerve function in ESKD.

Effects of hemodiafiltration and high flux hemodialysis on nerve excitability in end-stage kidney disease

OBJECTIVES

Peripheral neuropathy is the most common neurological complication in end-stage kidney disease. While high flux hemodialysis (HFHD) and hemodiafiltration (HDF) have become the preferred options for extracorporeal dialysis therapy, the effects of these treatments on nerve excitability have not yet been examined.

METHODS

An observational proof-of-concept study of nerve excitability and neuropathy was undertaken in an incident dialysis population (n = 17) receiving either HFHD or HDF. Nerve excitability techniques were utilised to assess nerve ion channel function and membrane potential, in conjunction with clinical assessment and standard nerve conduction studies. A mathematical model of axonal excitability was used to investigate the underlying basis of the observed changes. Nerve excitability was recorded from the median nerve, before, during and after a single dialysis session and correlated with corresponding biochemical markers. Differences in nerve excitability were compared to normal controls with longitudinal follow-up over an 18 month period.

RESULTS

Nerve excitability was performed in patient cohorts treated with either HFHD (n = 9) or online HDF (n = 8), with similar neuropathy status. Nerve excitability measures in HDF-treated patients were significantly closer to normal values compared to HFHD patients obtained over the course of a dialysis session (p<0.05). Longitudinal studies revealed stability of nerve excitability findings, and thus maintenance of improved nerve function in the HDF group.

CONCLUSIONS

This study has provided evidence that nerve excitability in HDF-treated patients is significantly closer to normal values prior to dialysis, across a single dialysis session and at longitudinal follow-up. These findings offer promise for the management of neuropathy in ESKD and should be confirmed in randomised trials.

Axonal dysfunction prior to neuropathy onset in type 1 diabetes

BACKGROUND

The present study was undertaken to determine whether there were changes evident in axonal membrane function prior to the onset of neuropathy in patients with type 1 and type 2 diabetes.

METHODS

From a cohort of 110 consecutive referrals, nerve excitability was investigated in 40 diabetic patients without clinical evidence of neuropathy (20 type 1 diabetic patients and 20 type 2 diabetic patients). Groups were matched for gender, disease duration and HbA(1c). Studies were also undertaken in two control groups, younger controls and older controls, matched for age and gender with the diabetic cohorts.

RESULTS

Subjects with type 1 diabetes demonstrated significant nerve excitability abnormalities when compared with younger normal controls. Specifically, type 1 subjects showed a significant reduction at multiple time points in both depolarising and hyperpolarising threshold electrotonus. Additionally, the relative refractory period was prolonged (type 1, 3.19 ms; younger normal controls, 3.0 ms; p < 0.05) and superexcitability was reduced (type 1, -23.12%; younger normal controls, -26.37%; p < 0.05), consistent with axonal membrane depolarisation. Correlations were identified in type 1 patients between disease duration and nerve excitability parameters, including the relative refractory period (r = -0.533, p < 0.05). In contrast, only minor non-specific changes were noted in the type 2 group.

DISCUSSION

This study provides clear evidence of altered axonal function in patients with type 1 diabetes in the absence of clinical neuropathy. These findings suggest that altered axonal membrane potential may precede neuropathy onset in type 1 diabetes and as such may indicate a window of opportunity to intervene and potentially reverse axonal membrane dysfunction before the development of irreversible neuropathy.

Axonal hyperpolarization in inclusion-body myopathy, Paget disease of the bone, and frontotemporal dementia (IBMPFD)

INTRODUCTION

Inclusion-body myopathy, Paget disease of the bone, and frontotemporal dementia (IBMPFD) is an autosomal dominant disorder due to mutations in the valosin-containing protein (VCP) gene. Patients with this disorder may have neuropathic or myopathic features.

METHODS

Peripheral nerve function and axonal excitability were studied in three members from two families with VCP mutations (p.Arg155Leu and p.Leu198Trp).

RESULTS

Patients from the first family had neurogenic patterns on needle electromyography (EMG), whereas those in the second family had myopathic EMG changes. In threshold electrotonus for motor axons, the changes to depolarizing and hyperpolarizing conditioning currents were at or outside control limits in all three patients. Superexcitability was increased, and the relative refractory period was reduced. The strength-duration time constant was normal. In sensory axons of all three patients, there were similar changes in threshold electrotonus, but not in superexcitability.

DISCUSSION

These features are best explained by axonal hyperpolarization. The findings provide insight into the pathophysiological mechanisms in these genotypes and, possibly, into all patients with IBMPFD.

Early, progressive, and sustained dysfunction of sensory axons underlies paclitaxel-induced neuropathy

Paclitaxel is used in the adjuvant treatment of breast cancer. It induces disabling and potentially long-lasting sensory neuropathy. This study systematically and prospectively investigated sensory function, using clinical grading scales, quantitative sensory testing, and neurophysiological and nerve excitability studies in 28 patients with early-stage breast cancer. After administration of 529 ± 41 mg/m(2) paclitaxel, 71% of patients developed neuropathic symptoms by 6 weeks of treatment. Early and progressive increases in stimulus threshold (P < 0.05) and reduction in sensory amplitudes from 47.0 ± 3.3 μV to 42.4 ± 3.4 μV (P < 0.05) occurred by 4 weeks, with a further reduction by final treatment (33.7 ± 3.0 μV, P < 0.001). The majority of patients (63%) did not experience recovery of neuropathic symptoms at follow-up. Axonal disruption did not relate to membrane conductance dysfunction. We found that paclitaxel produces early sensory dysfunction and leads to persistent neuropathy. Importantly, significant axonal dysfunction within the first month of treatment predated symptom onset, suggesting a window for neuroprotective therapies.

Acute, reversible axonal energy failure during stroke-like episodes in MELAS

The pathophysiology of stroke-like episodes in MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) remains unresolved. Possible mechanisms include mitochondrial angiopathy, cytopathy, or both, collectively resulting in cellular energy depletion. To clarify disease mechanisms, axonal excitability properties were investigated in a 10-year-old child with MELAS. Serial assessments during a stroke-like episode revealed reversible depolarization of the axonal membrane consistent with disruption of energy-dependent processes. Axonal parameters correlated with the clinical assessment of central dysfunction and biochemical measures of acidosis. Novel axonal excitability techniques have established acute, reversible ischemic-like depolarization that may serve as a surrogate marker of central events that develop during stroke-like episodes in MELAS.

Oxaliplatin-induced neurotoxicity: changes in axonal excitability precede development of neuropathy

Administration of oxaliplatin, a platinum-based chemotherapy used extensively in the treatment of colorectal cancer, is complicated by prominent dose-limiting neurotoxicity. Acute neurotoxicity develops following oxaliplatin infusion and resolves within days, while chronic neuropathy develops progressively with higher cumulative doses. To investigate the pathophysiology of oxaliplatin-induced neurotoxicity and neuropathy, clinical grading scales, nerve conduction studies and a total of 905 axonal excitability studies were undertaken in a cohort of 58 consecutive oxaliplatin-treated patients. Acutely following individual oxaliplatin infusions, significant changes were evident in both sensory and motor axons in recovery cycle parameters (P < 0.05), consistent with the development of a functional channelopathy of axonal sodium channels. Longitudinally across treatment (cumulative oxaliplatin dose 776 +/- 46 mg/m(2)), progressive abnormalities developed in sensory axons (refractoriness P < or = 0.001; superexcitability P < 0.001; hyperpolarizing threshold electrotonus 90-100 ms P < or = 0.001), while motor axonal excitability remained unchanged (P > 0.05), consistent with the purely sensory symptoms of chronic oxaliplatin-induced neuropathy. Sensory abnormalities occurred prior to significant reduction in compound sensory amplitude and the development of neuropathy (P < 0.01). Sensory excitability abnormalities that developed during early treatment cycles (cumulative dose 294 +/- 16 mg/m(2) oxaliplatin; P < 0.05) were able to predict final clinical outcome on an individual patient basis in 80% of patients. As such, sensory axonal excitability techniques may provide a means to identify pre-clinical oxaliplatin-induced nerve dysfunction prior to the onset of chronic neuropathy. Furthermore, patients with severe neurotoxicity at treatment completion demonstrated greater excitability changes (P < 0.05) than those left with mild or moderate neurotoxicity, suggesting that assessment of sensory excitability parameters may provide a sensitive biomarker of severity for oxaliplatin-induced neurotoxicity.

Axonal ion channels from bench to bedside: a translational neuroscience perspective

Over recent decades, the development of specialised techniques such as patch clamping and site-directed mutagenesis have established the contribution of neuronal ion channel dysfunction to the pathophysiology of common neurological conditions including epilepsy, multiple sclerosis, spinal cord injury, peripheral neuropathy, episodic ataxia, amyotrophic lateral sclerosis and neuropathic pain. Recently, these insights from in vitro studies have been translated into the clinical realm. In keeping with this progress, novel clinical axonal excitability techniques have been developed to provide information related to the activity of a variety of ion channels, energy-dependent pumps and ion exchange processes activated during impulse conduction in peripheral axons. These non-invasive techniques have been extensively applied to the study of the biophysical properties of human peripheral nerves in vivo and have provided important insights into axonal ion channel function in health and disease. This review will provide a translational perspective, focusing on an overview of the investigational method, the clinical utility in assessing the biophysical basis of ectopic symptom generation in peripheral nerve disease and a review of the major findings of excitability studies in acquired and inherited neurological disease states.

Neuromuscular disease in the dialysis patient: an update for the nephrologist

Neuromuscular disease is an extremely common complication of end-stage kidney disease (ESKD), manifesting in almost all dialysis patients, and leading to weakness, reduced exercise capacity, and disability. Recent studies have suggested that hyperkalemia may underlie the development of neuropathy. As such, maintenance of serum K(+) within normal limits between periods of dialysis in ESKD patients manifesting early neuropathic symptoms may reduce neuropathy development and progression. For patients with more severe neuropathic syndromes, increased dialysis frequency or a switch to high-flux dialysis may prevent further deterioration, while ultimately, renal transplantation is required to improve and restore nerve function. Exercise training programs are beneficial for ESKD patients with muscle weakness due to neuropathy or myopathy, and are capable of improving exercise tolerance and quality of life. Specific treatments have recently been evaluated for symptoms of autonomic neuropathy, including sildenafil for impotence and midodrine for intra-dialytic hypotension, and have been shown to be effective and well tolerated. Other important management strategies for neuropathy include attention to foot care to prevent callus and ulceration, vitamin supplementation, and erythropoietin. Treatment with membrane-stabilizing agents, such as amitryptiline and gabapentin, are highly effective in patients with painful neuropathy.

Acute abnormalities of sensory nerve function associated with oxaliplatin-induced neurotoxicity

PURPOSE

Neurotoxicity is becoming increasingly recognized as the major dose-limiting toxicity of oxaliplatin. Because the mechanism of oxaliplatin-induced neurotoxicity remains unclear, the present study investigated the potential of axonal excitability techniques in identifying pathophysiologic mechanisms and early markers of nerve dysfunction.

PATIENTS AND METHODS

Measures of sensory axonal excitability were recorded before and after infusion over 88 treatment cycles in 25 patients with colorectal cancer, who received a total oxaliplatin dose of 766 +/- 56 mg/m(2). Neurologic assessment, clinical rating scales, and routine nerve conduction studies were performed.

RESULTS

By completion of treatment, 16% of patients had developed severe (grade 3) neurotoxicity, and oxaliplatin dose reduction or cessation as a result of neurotoxicity was required in 40% of patients. Changes in axonal excitability occurred after infusion and could be explained on the basis of alterations in axonal membrane sodium (Na+) channel function (refractoriness: 7.6% +/- 1.7% before infusion v 4.5% +/- 1.4% after infusion; P = .03; superexcitability: -22.8% +/- 0.8% before infusion v -20.1% +/- 1.1% after infusion; P = .0002). Changes became less pronounced in later treatment cycles, suggesting that chronic nerve dysfunction and sensory loss masked acute effects at higher cumulative doses. Importantly, patients who demonstrated reductions in superexcitability in early treatment were subsequently more likely to develop moderate to severe neurotoxicity. The findings suggest that the degree of acute nerve dysfunction may relate to the development of chronic neurotoxicity.

CONCLUSION

Sensory axonal excitability techniques may facilitate identification of Na+ channel dysfunction in oxaliplatin-induced neurotoxicity and thereby provide a method to identify patients at risk for neurotoxicity to target those most likely to benefit from future neuroprotective strategies.