Motor unit number estimates and quantitative motor unit analysis in healthy subjects and patients with amyotrophic lateral sclerosis

Abstract

Limitations associated with global measures of function in patients with amyotrophic lateral sclerosis (ALS) and the qualitative nature of needle electromyography have stimulated the development of alternate means of monitoring disease severity and progression in ALS. Thus, the objective of this study was to examine the ability of one these techniques, decomposition-based quantitative electromyography (DQEMG), to obtain electrophysiological data, including motor unit number estimates (MUNEs), from a group of patients with ALS. The first dorsal interosseous and biceps brachii muscles were studied in 10 healthy subjects and 9 patients with ALS. Following the acquisition of a maximum M wave, needle- and surface-detected EMGs were collected simultaneously during 30-second contractions performed at 10% of the maximum voluntary contraction force to obtain motor unit potential (MUP) trains. DQEMG was then used to extract the surface-detected MUP associated with each MUP train, the mean size of which was divided into the maximum M wave to obtain a MUNE. The results suggest that quantitative electrophysiological data obtained using DQEMG are representative of the pathophysiological changes in the lower motor system in ALS patients, supporting its use in studies documenting the natural history and progression of the disease.

Probabilistic muscle characterization using QEMG: Application to neuropathic muscle

“…[12][13][14][15] These EMG signals were decomposed into MUP templates using DQEMG. 16 DQEMG typically finds 51 isolated MUPs produced by a single motor unit, aligns them, and uses a median trimmed average to form the MUP template.…”

Relationships between surface EMG variables and motor unit firing rates

“…The recruitment and rate coding strategy varies among muscles, and is seemingly dependent on the number of motor units and the function of the muscle. In the Wrst dorsal interosseous (FDI), for example, it is suggested that there are approximately 144 motor units, and evidence suggests that all of these motor units are typically recruited by approximately 60% maximal voluntary contraction (MVC) force (Boe et al 2007). Beyond 60% MVC in the FDI, rate coding is used to increase force.…”

“…Beyond 60% MVC in the FDI, rate coding is used to increase force. In the biceps brachii, it is estimated that there are between 271 and 360 motor units, and it is suggested that new motor units are recruited up to approximately 88% MVC (Boe et al 2007;Kukulka and Clamann 1981), relying solely on the rate coding for only approximately the highest 10-20% of MVC.…”

High inter-rater reliability in analyzing results of decomposition-based quantitative electromyography in subjects with or without neuromuscular disorder

“…Clinically this information is valuable in that it provides insight into the changes occurring at the level of the MU in response to disorders of the neuromuscular system. Evidence to support this has come from several studies, including the observation of decreased MU number estimates and increased MU size and complexity in patients with amyotrophic lateral sclerosis (ALS) (Boe et al, 2007) and Charcot-Marie Tooth (CMT) disease (Shy et al, 2007), in addition to demonstrating age-related MU remodeling and an associated decrease in the estimated numbers of MUs in old and very old men (McNeil et al, 2005).…”