Single fibre electromyographic jitter in multiple sclerosis

Peripheral nervous system in multiple sclerosis-understanding the involvement via autonomic nervous system

AIM

The aim of this review is to summarize the clinical and paraclinical findings that demonstrate that multiple sclerosis (MS) affects the peripheral nervous system (PNS) as well as the central nervous system (CNS). Methods: Narrative review.

RESULTS

MS is traditionally defined as a chronic demyelinating immune-mediated disease of the CNS. However, there is emerging evidence that MS is a disease that does not solely affect the CNS but can manifest with PNS involvement as well. Several pathology studies have reported on signs of demyelination in the PNS, as well as on structural and functional involvement of the PNS in persons with MS (pwMS). From the functional aspect, several studies have shown autonomic nervous system (ANS) involvement in the form of sudomotor dysfunction measured with quantitative sudomotor axon reflex test (QSART) in different stages of MS, adding to the growing body of evidence that indicate PNS involvement in MS. In this review the clinical, pathological, neurophysiological, and imaging findings that demonstrate that MS affects the PNS as well as the CNS are summarized, with the emphasis on the ANS abnormalities.

CONCLUSION

Further large-scale research is needed in order to fully understand the frequency and importance of PNS affection in MS.

Long-Term High-Density Extracellular Recordings Enable Studies of Muscle Cell Physiology

Skeletal (voluntary) muscle is the most abundant tissue in the body, thus making it an important biomedical research subject. Studies of neuromuscular transmission, including disorders of ion channels or receptors in autoimmune or genetic neuromuscular disorders, require high-spatial-resolution measurement techniques and an ability to acquire repeated recordings over time in order to track pharmacological interventions. Preclinical techniques for studying diseases of neuromuscular transmission can be enhanced by physiologic ex vivo models of tissue-tissue and cell-cell interactions. Here, we present a method, which allows tracking the development of primary skeletal muscle cells from myoblasts into mature contracting myotubes over more than 2 months. In contrast to most previous studies, the myotubes did not detach from the surface but instead formed functional networks between the myotubes, whose electrical signals were observed over the entire culturing period. Primary cultures of mouse myoblasts differentiated into contracting myotubes on a chip that contained an array of 26,400 platinum electrodes at a density of 3,265 electrodes per mm². Our ability to track extracellular action potentials at subcellular resolution enabled study of skeletal muscle development and kinetics, modes of spiking and spatio-temporal relationships between muscles. The developed system in turn enables creation of a novel electrophysiological platform for establishing ex vivo disease models.

Patterns and significance of concomitant central and peripheral inflammatory demyelination

Inflammatory demyelinating diseases comprise a spectrum of disorders that affect central nervous system (CNS) and peripheral nervous system (PNS) myelin. Most individuals have demyelinating disease restricted to one or the other compartment but patients with concomitant CNS and PNS inflammatory inflammatory demyelinating processes have been reported not infrequently. In most such patients, involvement of either the CNS or the PNS predominates the clinical picture. Involvement of the other compartment is usually mild or subclinical with unclear prognostic and therapeutic implications. Similarly, while experimentally induced demyelinating disease in animal models is usually CNS or PNS predominant, varying degrees of pathology in the other system can occur depending on the species, type of immunogen, and genetic background of the immunized animal. When CNS and PNS demyelinating diseases occur concurrently, effective treatment for CNS disease can be safely combined with effective treatment for PNS disease.

The sad plight of multiple sclerosis research (low on fact, high on fiction): critical data to support it being a neurocristopathy

The literature for evidence of autoimmunity in multiple sclerosis (MS) is analysed critically. In contrast to the accepted theory, the human counterpart of the animal model experimental autoimmune demyelinating disease, experimental allergic encephalomyelitis (EAE), is not MS but a different demyelinating disorder, i.e. acute disseminated encephalomyelitis and acute haemorrhagic leucoencephalitis. Extrapolation of EAE research to MS has been guided largely by faith and a blind acceptance rather than sound, scientific rationale. No specific or sensitive immunological test exists that is diagnostic of MS despite the extensive application of modern technology. Immunosuppression has failed to have any consistent effect on prognosis or disease progression. The available data on MS immunotherapy are conflicting, at times contradictory and are based on findings in animals with EAE. They show predominantly a 30% effect in relapsing/remitting MS which suggests powerful placebo effect. Critical analysis of the epidemiological data shows no association with any specific autoimmune diseases, but does suggest that geographic factors and age at development posit an early onset possibly dependent on environmental influences. Certain neurological diseases are, however, found in association with MS, namely hypertrophic peripheral neuropathy, neurofibromatosis-1, cerebral glioma, glioblastoma multiforme and certain familial forms of narcolepsy. These share a common genetic influence possibly from genes on chromosome 17 affecting cell proliferation. A significant number of these disorders are of neural crest origin, the classical example being abnormalities of the Schwann cell. These and other data allow us to propose that MS is a developmental neural crest disorder, i.e. a cristopathy, implicating glial cell dysfunction with diffuse blood-brain barrier breakdown. The data on transcription factor SOX10 mutations in animals may explain these bizarre clinical associations with MS and the phenotypic variability of such alterations (Cossais et al. 2010). Research directed to the area of neural crest associations is likely to be rewarding.

Alteration of motor nerve recovery cycle in multiple sclerosis

OBJECTIVE

To study peripheral motor nerve excitability in patients with multiple sclerosis (MS).

METHODS

Twenty MS patients with normal nerve conduction parameters and no predisposing factors for peripheral neuropathy were included. Compound muscle action potentials were recorded from the abductor digiti minimi muscle to paired-pulse stimulation of the ulnar nerve at the wrist, with various interstimuli intervals (ISIs) ranging from 1 to 7 ms. The motor nerve recovery cycle was studied using a subtraction method. We measured the durations of the absolute and relative refractory periods (ARP, RRP) and the percentages of refractoriness and supernormality at 2.6 and 7 ms ISIs. The results obtained in MS patients were compared to normative values established in 20 age-matched healthy subjects. Correlations were made between excitability parameters and MS type (relapsing-remitting or progressive), EDSS score, disease duration, and motor evoked potential (MEP) abnormalities.

RESULTS

Supernormality was extremely reduced, refractoriness was increased and both ARP and RRP were prolonged in MS patients vs. healthy controls. These alterations did not correlate to clinical features or to the presence of MEP abnormalities.

CONCLUSIONS

Changes in motor nerve recovery cycle revealed the existence of subtle impairment in the peripheral nervous system of MS patients, mainly characterized by a reduced supernormality.

SIGNIFICANCE

Peripheral nerve excitability alterations in MS may be due to axoglial paranodal dysjunction or juxtaparanodal dysfunction.

Interferon causes no myasthenia in a seropositive patient with multiple sclerosis

We describe a successful outcome of long-term interferon beta-1b therapy in a patient who had multiple sclerosis (MS) with positive serum autoantibody to muscle acetylcholine receptor (AChR-Ab). Because of the reported possible causative linkage between interferon beta-1b and myasthenia gravis (MG), the presence of the pathogenic antibody complicated therapeutic strategies. We carefully observed the patient for further 6 months before the treatment, excluding symptomatic MG. The interferon beta-1b therapy then provided a clinical benefit. Hopefully this report will allow MS patients in similar situations to make more rapid, unprejudiced judgments than our patients.

Endplate dysfunction in healthy muscle following a period of disuse

The objective of this study was to test the hypothesis that muscle disuse can result in abnormal neuromuscular transmission. Six healthy volunteers (2 females, mean age = 33 years) participated in the study. Cast immobilization of one leg, for a period of 4 weeks, was used as a model of disuse; the contralateral leg was used as a control. Three testing sessions, consisting of stimulation single fiber electromyography of the soleus muscle bilaterally, were done before, immediately after, and 4 weeks after cast removal. The main outcome measure was neuromuscular jitter, measured as the mean of the consecutive differences (MCD) of single muscle fiber potentials. A mean MCD was calculated for each muscle, and the data from all subjects was pooled to calculate a sample mean MCD. The control side showed good reproducibility of results between testing sessions. The experimental side showed a significant increase of the sample mean MCD after casting when compared to: preimmobilization values (P < 0.001), and to the control side (P < 0.001). After 4 weeks of recovery, the sample mean MCD returned to preimmobilization values. This study presents evidence that muscle disuse, without any neuromuscular disease, can result in a reversible dysfunction of neuromuscular transmission.

Peripheral neuropathy in multiple sclerosis: a clinical and electrophysiologic study

Peripheral nerve abnormalities are uncommon in multiple sclerosis (MS). When present, they are usually attributed to factors associated with advanced disease, such as malnutrition or cytotoxic drugs. We prospectively evaluated 22 mildly disabled MS patients with sensory complaints for evidence of neuropathy using the Neuropathy Symptom Score (NSS), clinical examination, and electrophysiologic studies of peripheral nerves. Distal latency, F-wave response, and nerve conduction velocity (NCV) and amplitude in the ulnar, median, tibial, peroneal and sural nerves were examined. Neuropathy was recorded if electrophysiologic abnormalities were detected in at least two peripheral nerves in the same patient. The most frequent electrophysiologic abnormalities noted were prolonged F-wave response and low motor amplitude in the peroneal nerve, slow sensory conduction velocities of the ulnar and sural nerves, and prolonged distal latencies in the sensory ulnar and sural nerves. Electrophysiologic abnormalities were found in 33 of 244 nerves examined (14.7%) and occurred in 10 patients (45.5%). Neuropathic symptoms were mild and did not correlate with electrophysiologic abnormalities. Age, disease duration, disease course and neurologic disability as evaluated by the Kurtzke Expanded Disability Status Scale, were not associated with the presence of neuropathy. Our findings indicate a high frequency of sensory-motor neuropathy in a selected group of MS patients.

Peripheral sensory abnormalities in patients with multiple sclerosis

Although multiple sclerosis primarily affects myelin within the central nervous system, both pathologic and physiological studies suggest that mild deficits in peripheral nervous system myelin may be common. To evaluate this question further, we performed near nerve studies on sural nerves of 14 patients with multiple sclerosis. Peak-to-peak amplitude and maximum conduction velocity were normal in 9 of 14 patients, while minimum conduction velocity, or the velocity of the slowest-conducting component of the sensory action potential, was abnormally reduced in 9 patients. In addition, the supernormal period was evaluated for patients and compared with a control sample; multiple sclerosis patients showed a significant reduction in the amplitude of supernormality. Both the reduction in minimum conduction velocity and the alteration in the supernormal period are consistent with a mild defect in peripheral myelin.

The peripheral nervous system in multiple sclerosis. A review and pathogenetic hypothesis

Despite the rarity of such observations in autopsy material, peripheral nervous system involvement in patients with multiple sclerosis is more common than suspected, judging from results of sophisticated electrophysiological and teased nerve fiber studies. The existence of a number of well documented cases of overt peripheral neuropathy in MS patients suggests that an etiological link may exist between the two conditions. The proposal has been made that one of the obligatory steps in the pathogenesis of MS is an alteration of the blood-brain barrier, which results in most instances from an immunologically induced vasculopathy due to a non-specific viral infection. Whereas the CNS responds by the formation of MS plaques, the PNS lesion is that of the typical post-infectious inflammatory polyneuropathy. In some MS patients an unusual degree of immunological vulnerability causes onion-bulb formations to develop as a result of repeated antigenic challenges. In MS patients the onion-bulb formation is the PNS analog of the CNS plaque: both result from the same pathogenetic mechanism.

Demyelinating optic neuropathy with Miller-Fisher syndrome. The case for overlap syndromes with central and peripheral demyelination

The syndrome of ataxia, areflexia and ophthalmoplegia, or Miller-Fisher syndrome, has been considered to be a variant of Guillain-Barré syndrome with pathology restricted to the peripheral nervous system. A patient with Miller-Fisher syndrome and bilateral demyelinating optic neuropathy suggesting associated central nervous system pathology is presented. Clinical and experimental evidence regarding the association of central and peripheral nervous system demyelination is reviewed.

A case of myasthenia gravis associated with optic neuritis

A case of myasthenia gravis is described in association with optic neuritis in which brain-stem auditory and somatosensory evoked potentials were normal. CSF contained alkaline oligoclonal IgG bands. Blood lymphocyte subpopulations showed a decreased number of T-suppressor cells.

Altered supernormality in multiple sclerosis peripheral nerve

Supernormality is a regular part of the recovery cycle of nerve. Supernormality was expressed in terms of amplitude, and in 20 control subjects the mean (S2 conditioned/S2 unconditioned) ratio of the median sensory nerve action potential amplitude recorded at the elbow measured 285 +/- 174 (range 119 to 783). A supramaximal conditioning shock was delivered 6 msec in advance of the test pulse. Seventeen (42.5%) of 40 patients with multiple sclerosis (MS) failed to demonstrate supernormality, the (S2 conditioned/S2 unconditioned) ratio being less than 100. This abnormality probably reflects a delay in recovery cycle and is additional evidence implicating peripheral nervous system involvement in multiple sclerosis.

Motor unit potential abnormalities in multiple sclerosis: further evidence for a peripheral nervous system defect

We have recently reported abnormalities of single fibre EMG in patients with multiple sclerosis. The present study applies quantitative electrophysiological techniques to the same group of patients. The number of motor units in the extensor digitorum brevis muscle was measured and their characteristics recorded. Also the shortest distal motor latency and fastest motor conduction velocities were estimated. Abnormalities suggesting a patchy denervating/reinnervating process due to pathology in the intramuscular nerve network or at the endplate were found in a number of patients. There was a good correlation between patients with abnormal motor unit potentials and those with abnormal single fibre EMG "jitter".