Search

Objective: To assess the repeatability and suitability for multicentre studies of MScanFit motor unit number estimation (MUNE), which involves modelling compound muscle action potential (CMAP) scans. Methods: Fifteen groups in 9 countries recorded CMAP scans twice, 1–2 weeks apart in healthy subjects from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. The original MScanFit program (MScanFit-1) was compared with a revised version (MScanFit-2), designed to accommodate different muscles and recording conditions by setting the minimal motor unit size as a function of maximum CMAP. Results: Complete sets of 6 recordings were obtained from 148 subjects. CMAP amplitudes differed significantly between centres for all muscles, and the same was true for MScanFit-1 MUNE. With MScanFit-2, MUNE differed less between centres but remained significantly different for APB. Coefficients of variation between repeats were 18.0% for ADM, 16.8% for APB, and 12.1% for TA. Conclusions: It is recommended for multicentre studies to use MScanFit-2 for analysis. TA provided the least variable MUNE values between subjects and the most repeatable within subjects. Significance: MScanFit was primarily devised to model the discontinuities in CMAP scans in patients and is less suitable for healthy subjects with smooth scans.

Background Nerve excitability testing by threshold-tracking is the only available method to study axonal ion channel function and membrane potential in the clinical setting. The measures are, however, indirect and the interpretation of neuropathic changes remains challenging. The same multiple measures of axonal excitability were adapted to further explore the pathophysiological changes in rodent disease models under pharmacologic and genetic manipulations. These studies are typically limited to the investigation of the “long nerves” such as the tail or the tibial nerves. New method We introduce a novel setup to explore the ulnar nerve excitability in rodents. We provide normative ulnar data in 11 adult female Long Evans rats under anaesthesia by comparison with tibial and caudal nerves. Additionally, these measures were repeated weekly on 3 occasions to determine the repeatability of these tests. Results Nerve excitability assessment of ulnar nerve proved to be a longitudinally repeatable measure of axonal function mature in rats, as were measures in tibial and caudal nerves. Comparison with existing method: Ulnar nerve motor excitability measures were different from the caudal and tibial excitability measures. Most notably, ulnar nerve showed the largest threshold changes during both depolarizing and hyperpolarizing threshold electrotonus. Conclusions Ulnar nerves demonstrate a distinct nerve excitability profile than the caudal and tibial nerves which could have functional and pathological implications.

Contains fulltext : 167925.pdf (Publisher’s version ) (Open Access), See Cannon (doi:10.1093/brain/awv400) for a scientific commentary on this article.Congenital myopathies are a clinically and genetically heterogeneous group of muscle disorders characterized by congenital or early-onset hypotonia and muscle weakness, and specific pathological features on muscle biopsy. The phenotype ranges from foetal akinesia resulting in in utero or neonatal mortality, to milder disorders that are not life-limiting. Over the past decade, more than 20 new congenital myopathy genes have been identified. Most encode proteins involved in muscle contraction; however, mutations in ion channel-encoding genes are increasingly being recognized as a cause of this group of disorders. SCN4A encodes the alpha-subunit of the skeletal muscle voltage-gated sodium channel (Nav1.4). This channel is essential for the generation and propagation of the muscle action potential crucial to muscle contraction. Dominant SCN4A gain-of-function mutations are a well-established cause of myotonia and periodic paralysis. Using whole exome sequencing, we identified homozygous or compound heterozygous SCN4A mutations in a cohort of 11 individuals from six unrelated kindreds with congenital myopathy. Affected members developed in utero- or neonatal-onset muscle weakness of variable severity. In seven cases, severe muscle weakness resulted in death during the third trimester or shortly after birth. The remaining four cases had marked congenital or neonatal-onset hypotonia and weakness associated with mild-to-moderate facial and neck weakness, significant neonatal-onset respiratory and swallowing difficulties and childhood-onset spinal deformities. All four surviving cohort members experienced clinical improvement in the first decade of life. Muscle biopsies showed myopathic features including fibre size variability, presence of fibrofatty tissue of varying severity, without specific structural abnormalities. Electrophysiology suggested a myopathic process, without myotonia. In vitr

Mice deficient of myelin protein zero (P0) are established models of demyelinating Charcot-Marie-Tooth (CMT) disease. Recent work form our laboratory indicated that in severely affected P0−/− as well as in P0+/− (modeling CMT1B), the neuropathy is aggravated by associated changes in voltage-gated Na + channel isoforms with ectopic expression of NaV1.8 on motor axons. This raised the hypothesis that treatments with NaV1.8 blockers could be used in treatment strategies to improve the motor function in these models. We investigated the effect of the NaV1.8 subtype selective blocker A-803467 and of the novel blocker Compound 31 (C31, Bioorg Med Chem Lett 2010, 20, 6812; AbbVie Inc.) which can be orally administered. Double P0 and NaV1.8 knockouts were used as controls. Multiple measures of tibial nerve excitability by “threshold-tracking” were used to monitor the acute changes in motor axon membrane function up to 2 hours after the blockers. Overall, the baseline excitability measures were much more abnormal in P0−/− at 4 months as compared to P0+/− at 20 months. Nevertheless, in both models, the NaV1.8 blockers produced similar deviations in excitability at a dose of 100 mg/Kg. Most notably, the deviations during both depolarizing and hyperpolarizing threshold electrotonus were increased. Optimizing the parameters of the “Bostock” nodal-internodal myelinated motor axon mathematical model indicated a hyperpolarizing change in resting membrane potential. Our data suggest that ectopic NaV1.8 expression causes a state of motor axon depolarization which can be reversed by pharmacologic NaV1.8 blockers. Measures of axonal excitability could be used to monitor the functional consequence of NaV1.8 blockers in future therapeutic studies.

Prolonged high frequency electrical stimulation (RS) was found to precipitate motor axon degeneration in P0+/− mice, a model of demyelinating Charcot-Marie-Tooth disease (CMT1B). We hypothesized that this was due to the associated changes in voltage-gated Na + channel (VGSC) isoforms with ectopic expression of NaV1.8 on motor axons. The aim of this study was to investigate whether the increased RS toxicity in P0+/− can be attenuated by both the non-selective VGSC blocker lamotrigine and by a novel NaV1.8 subtype selective blocker (Compound 31, Bioorg. Med. Chem. Lett. 2010, 20, 6812; AbbVie Inc.). Investigations were carried out in 1-year-old WT, P0+/− and NaV1.8 knockouts (P0+/−SNS) mice. Tibial nerve RS was carried out under anesthesia using interrupted trains of 200 Hz for 3 hours, which is not neurotoxic in WT. Nerve function was monitored by conventional conduction studies and nerve excitability measures by threshold-tracking. Electrophysiological and histological outcome measures were compared at 3 days after RS to allow for axonal degeneration to occur. Following RS, the CMAP amplitude of P0+/− remained reduced to 50% in association with signs of ongoing axonal degeneration. This toxicity of RS in P0+/− could be largely attenuated by pretreatment with lamotrigine. Furthermore, a similar attenuation was observed in P0+/− following pre-treatment with Compound 31 as well as in P0+/− SNS. Our data suggest that increased toxicity of RS on motor axons in P0+/− could be attributed to an increased activity-dependent Na+ influx, especially through NaV1.8. This raises hope that subtype-selective VGSC blockers could be neuroprotective for motor function in CMT1B.

We have developed an EMG decomposition system called EMGTools that can extract the constituent MUAPs and firing patterns for quantitative analysis from the EMG signal recorded at slight effort for clinical evaluation. The aim was to implement a robust system able to handle the challenges and variations in clinically recorded signals. The system extracts MUAPs recorded by concentric needle electrodes and resolves superimposed MUAPs to produce firing patterns (FPs). Thus, critical fixed thresholds/parameters are avoided and replaced with adaptive solutions. The decomposition algorithm consists of three stages: segmentation, clustering and resolution of compound segments. The results are validated using three different methods, comparing mean MUAP duration with previous methods, comparing dual channel recordings, and assessing the residual signal after a decomposition. The advantages and limitations of the system are discussed.

Udgivelsesdato: 2008/3/17

Udgivelsesdato: 2008/1

Udgivelsesdato: 2008/3/17

Udgivelsesdato: 2008/6

Udgivelsesdato: 2008/6

Although it is well known that cisplatin causes a sensory neuropathy, the primary site of involvement is not established. The clinical symptoms localized in a stocking-glove distribution may be explained by a length dependent neuronopathy or by a distal axonopathy. To study whether the whole neuron or the distal axon was primarily affected, we have carried out serial clinical and electrophysiological studies in 16 males with testicular cancer before or early and late during and after treatment with cisplatin, etoposide and bleomycin at limited (400 mg/m2 cisplatin) doses. At cumulative doses of cisplatin higher than 300 mg/m2 the patients lost distal tendon and H-reflexes and displayed reduced vibration sense in the feet and the fingers. The amplitudes of sensory nerve action potentials (SNAP) from the fingers innervated by the median nerve and the dorsolateral side of the foot innervated by the sural nerve were 50-60% reduced, whereas no definite changes occurred at lower doses. The SNAP conduction velocities were reduced by 10-15% at cumulative doses of 400-700 mg/m2 consistent with loss of large myelinated fibres. SNAPs from primarily Pacinian corpuscles in digit 3 and the dorsolateral side of the foot evoked by a tactile probe showed similar changes to those observed in SNAPs evoked by electrical stimulation. At these doses, somatosensory evoked potentials (SEPs) from the tibial nerve had increased latencies of peripheral, spinal and central responses suggesting loss of central processes of large dorsal root ganglion cells. Motor conduction studies, autonomic function and warm and cold temperature sensation remained unchanged at all doses of cisplatin treatment. The results of these studies are consistent with degeneration of large sensory neurons whereas there was no evidence of distal axonal degeneration even at the lowest toxic doses of cisplatin.

Udgivelsesdato: 2007-Feb, AIM: Following Wallerian degeneration, peripheral myelinated axons have the ability to regenerate and, given a proper pathway, establish functional connections with targets. In spite of this capacity, the clinical outcome of nerve regeneration remains unsatisfactory. Early studies have found that regenerated internodes remain persistently short though this abnormality did not seem to influence recovery in conduction. It remains unclear to which extent abnormalities in axonal function itself may contribute to the poor outcome of nerve regeneration. METHODS: We review experimental evidence indicating that internodes play an active role in axonal function. RESULTS: By investigating internodal contribution to axonal excitability we have found evidence that axonal function may be permanently compromised in regenerated nerves. Furthermore, we illustrate that internodal function is also abnormal in regenerated human nerves. CONCLUSION: The data suggest that persistently shorter regenerated internodes lead to increased Na+/K+-pump activity in response to increased Na+ entry during conduction. This may impair axonal function during prolonged repetitive activity and drain the energy reserves of the axons.

Udgivelsesdato: 2005-null, The aim of this study was to establish a nerve lesion model to compare serial electrophysiological and functional outcome measures with histological findings. The relative significance of the parameters in lesions of diverse severity, the time course of recovery, and the tools for serial longitudinal studies after nerve lesions were studied in rats. We compared weekly electrophysiological and functional studies for 100 or 150 days in rats after crush or section/suture of the sciatic nerve at midthigh level. Finally, tibial nerves were taken for histology. We confirmed that recovery was faster and more complete in nerves regenerating after crush than after section, irrespective of method of evaluation. Furthermore, continuous maturational changes occurred in control nerves, and such continuous growth-related changes should be taken into account when evaluating maturational changes during nerve regeneration. A lack of correlation between evaluation methods supports that functional, morphological, and physiological parameters show different aspects of the recovery process after nerve lesions, and that these outcome measures should be included separately in therapeutic studies.

Complex forms of hereditary spastic paraplegia (HSP) are rare and usually transmitted in an autosomal recessive pattern. A family of four generations with autosomal dominant hereditary spastic paraplegia (AD-HSP) and a complex phenotype with variably expressed co-existing ataxia, dysarthria, unipolar depression, epilepsy, migraine, and cognitive impairment was investigated. Genetic linkage analysis and sequencing of the SPG4 gene was performed and electrophysiologic investigations were carried out in six individuals and positron emission tomography (PET) in one patient. The disease was linked to the SPG4 locus on chromosome 2p as previously reported for pure HSP. Sequence analysis of the SPG4 (spastin) gene identified a novel 1593 C > T (GLN490Stop) mutation leading to premature termination of exon 12 with ensuing truncation of the encoded protein. However, the mutation was only identified in those individuals who were clinically affected by a complex phenotype consisting of HSP and cerebellar ataxia. Other features noted in this kindred including epilepsy, cognitive impairment, depression, and migraine did not segregate with the HSP phenotype or mutation, and therefore the significance of these features to SPG4 is unclear. Electrophysiologic investigation showed increased central conduction time at somatosensory evoked potentials measured from the lower limbs as the only abnormal finding in two affected individuals with the SPG4 mutation. Moreover, PET of one patient showed significantly relatively decreased regional cerebral blood flow in most of the cerebellum. We conclude that this kindred demonstrates a considerable overlap between cerebellar ataxia and spastic paraplegia, emphasizing the marked clinical heterogeneity of HSP associated with spastin mutations