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Introduction: The aim of this study was to determine whether electrically evoked multiplet discharges (MDs) are related to severity of clinical deterioration in motor neuron disease (MND).Methods: Stimulated high-density surface electromyographic (HDsEMG) recordings were performed in thenar muscles. Data were collected from 31 MND patients. MDs from the HDsEMG recordings were determined at baseline. ALSFRS-R scores were obtained at baseline and at a maximum of 16 weeks follow-up.Results: The presence of MDs was associated with progressive deterioration of ALSFRS-R score (P = 0.02) and fine motor function (FMF) (P < 0.001). Patients who had a higher number of motor units that generated MDs (r = 0.61, P < 0.001) and patients who had a higher number of MDs (as percentage of applied stimuli) (r = 0.59, P = 0.001) had a more severe decline in FMF.Conclusions: Electrically evoked MDs are associated with more marked clinical deterioration in patients with MND. [ABSTRACT FROM AUTHOR]

Objective: To determine and compare the diagnostic accuracy of electrically elicited multiplet discharges (MDs) and fasciculation potentials (FPs) in motor neuron disease (MND).Methods: Patients were eligible when they had MND in their differential diagnosis and were referred for electromyogram (EMG). Stimulated high-density surface EMG of the thenar muscles was performed on the same day as standard EMG examination. High-density recordings were analysed for presence of MDs and needle EMG of any muscle investigated in the cervical region for presence of FPs.Results: Of the 61 patients enrolled in this diagnostic study, 24 patients were clinically diagnosed with amyotrophic lateral sclerosis (ALS) and 11 patients with progressive muscular atrophy (PMA). Another diagnosis was made in 26 patients. Sixteen patients in whom MDs were detected were diagnosed with either ALS (n = 11) or PMA (n = 5; sensitivity = 47.1%, PPV = 94.1%). MDs were detected in only one patient initially diagnosed with PMA, but in whom later on, multifocal motor neuropathy could not be excluded (specificity = 96.2%). Electrically elicited MDs had a higher specificity than FPs (96.2% vs 53.9%, p < 0.001, n = 26) and lower sensitivity (47.1% vs 85.3%, p = 0.002, n = 34). When considering presence of MDs in MND as neurogenic EMG abnormality, lower motor neuron involvement of ≥ 1 EMG region increased from 50% to 73.5% (p = 0.008, n = 34).Conclusions: Electrically evoked MDs are highly specific for ALS and PMA and are an early sign of lower motor neuron dysfunction. [ABSTRACT FROM AUTHOR]

Amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA) are characterized by a loss of motor units (MUs), reinnervation and, eventually, muscle fibre loss. These three aspects are all reflected in the compound muscle action potential scan (CMAP scan, a high-detail stimulus response curve), which visualizes large MU potentials as 'steps'. We explored changes in the CMAP scan over time, combined the information on steps and CMAP amplitude into a CMAP scan-based progression score (CSPS), and correlated this score with motor unit number estimates (MUNE). Ten patients (three PMA, seven ALS; age 37−77 years) were included. CMAP scan and MUNE measurements were performed five times during a three-month period. Nine patients had additional measurements. The follow-up period was 3−24 months. Results demonstrated that abnormalities in steps preceded a decline in maximum CMAP amplitude during follow-up. Usually, both steps and maximum CMAP amplitude changed between recordings. The correlation between the CSPS and MUNE was −0.80 ( p < 0.01). In conclusion, the CMAP scan can be used to visualize and quantify disease progression in a muscle affected by MND. The CSPS is a measure of MU loss that is quick and easy to obtain and that, in contrast to MUNE, has no sample bias. [ABSTRACT FROM AUTHOR]

Typical Miller Fisher syndrome (MFS) lacks limb muscle weakness, but some patients may unpredictably progress to severe Guillain-Barré syndrome. The compound muscle action potential (CMAP) scan is a recently developed non-invasive, painless, and reproducible method for detecting early changes in motor nerve excitability. This technique was used to monitor subclinical limb motor nerve dysfunction during disease course in typical MFS. Three Miller Fisher patients with preserved limb muscle strength and normal routine nerve conduction studies were included. Frequent serial CMAP scanning of the median nerve was performed during acute phase and follow-up and was related to clinical course and outcome. All patients showed an abnormal increase in the range of stimulus intensities at the day of hospital admission, indicating reduced motor nerve excitability already at the earliest stage of disease. Median nerve dysfunction progressed in parallel or even before clinical deterioration, and improved with clinical recovery. Our study shows that typical MFS is a more general neuropathy, affecting peripheral motor nerves even in patients with preserved limb strength and conduction velocity. CMAP scanning is a sensitive technique for early detection of subclinical motor nerve dysfunction and for monitoring disease activity in immune-mediated neuropathies. [ABSTRACT FROM AUTHOR]

We hypothesized that action potentials evoked by distal stimulation might trigger ectopic activity (multiplet discharges, MDs). By studying MDs, we investigated the involvement of the axonal part of the peripheral motor neuron in amyotrophic lateral sclerosis (ALS) and progressive muscular atrophy (PMA). We performed stimulated high-density surface EMG recordings of the thenar muscles in 10 ALS/PMA patients, five recordings per patient over a three-month period. Furthermore, motor unit number estimates (MUNE) and ALSFRS-R scores were obtained in sessions 1 and 5. MDs were found in all patients, in 21% of the sampled motor units, and in response to 2.4% of the stimulations. The interspike interval range of the MD components was 2.9-6.5 ms, which is compatible only with a distal MD origin. The number of MDs, as percentage of the number of applied stimuli, was correlated with a decline in ALSFRS-R ( r =0.80, p =0.006) and MUNE ( r =0.72, p =0.02). In conclusion, MDs can be elicited with electrical stimulation in ALS and PMA patients. Analysis of MD characteristics provides further indications for pathophysiological excitability changes in the most distal part of the motor neuron. MDs are associated with clinical deterioration. [ABSTRACT FROM AUTHOR]

Objective To determine whether there is a relation between electrically evoked multiplet discharges (MDs) and motor axonal excitability properties. We hypothesized that electrically evoked MDs share their underlying pathophysiological mechanism with fasciculations. Methods High-density surface EMG and motor nerve excitability recordings of the thenar muscles were performed in 22 patients with motor neuron disease (MND) in their differential diagnosis and who were referred for EMG examination. Results Supernormality (hyperexcitable phase following the refractory period) was significantly increased in patients with MDs ( n = 10) compared to patients without MDs ( n = 12) (25.5% vs 17.0%; p = 0.02). Depolarizing threshold electrotonus differed significantly between both groups as well (TEdpeak, 76.6% vs 66.6%, p < 0.01; TEd90-100 ms, 51.7% vs 44.3%, p < 0.01) Conclusions Our findings imply that the same pathophysiological excitability changes are involved in generating MDs and fasciculations. Yet, MDs may be quantified more easily, and may be more specific for abnormal distal excitability than fasciculations, because fasciculations may originate along the motor axon as well as in the neuron cell body. Significance MDs are potentially useful as objective measure of increased distal axonal excitability at individual motor unit level and might complement clinical studies in MND. [ABSTRACT FROM AUTHOR]