The utility of motor unit number estimation methods versus quantitative motor unit potential analysis in diagnosis of ALS.

OBJECTIVE: To compare the diagnostic utility of motor unit number estimation (MUNE) methods to motor unit potential (MUP) analysis in amyotrophic lateral sclerosis (ALS). METHODS: Twenty-five patients (1 definite, 11 probable, 9 possible ALS and 4 progressive muscular atrophy) and 22 healthy controls were prospectively included. Quantitative MUP analysis and three MUNE methods; Multiple Point Stimulation MUNE (MPS), Motor Unit Number Index (MUNIX) and MScanFit MUNE (MScan) were done in abductor pollicis brevis muscle. The sensitivities were compared by McNemar chi-square test. MUNE, MUP and revised ALS Functional Rating Scale (ALSFRS-R) parameters were correlated by regression analysis. RESULTS: The sensitivities of MPS (76%) and MScan (68%) were higher than MUP duration (36%) and amplitude (40%) in detecting motor unit loss (p < 0.05). MUNE methods increased the categorical probability from possible to probable ALS in 4 patients (16%). There was only significant correlation between ALSFRS-R and MScan (r = 0.443, p = 0.027) among the electrophysiological tests. MUNE methods did not correlate to MUP parameters. CONCLUSIONS: MUNE methods are more sensitive in showing abnormality than MUP analysis. SIGNIFICANCE: MUNE methods, in particular MScan, may have the potential to be implemented in the clinical practice for diagnosis and follow-up of neuromuscular disorders particularly ALS.

Reproducibility, and sensitivity to motor unit loss in amyotrophic lateral sclerosis, of a novel MUNE method: MScanFit MUNE.

OBJECTIVE: To examine inter- and intra-rater reproducibility and sensitivity to motor unit loss of a novel motor unit number estimation (MUNE) method, MScanFit MUNE (MScan), compared to two traditional MUNE methods; Multiple point stimulation MUNE (MPS) and Motor Unit Number Index (MUNIX). METHODS: Twenty-two ALS patients and 20 sex- and age-matched healthy controls were included. MPS, MUNIX, and MScan were performed twice each by two blinded physicians. Reproducibility of MUNE values was assessed by coefficient of variation (CV) and intra class correlation coefficient (ICC). Ability to detect motor unit loss was assessed by ROC curves and area under the curve (AUC). The times taken for each of the methods were recorded. RESULTS: MScan was more reproducible than MPS and MUNIX both between and within operators. The mean CV for MScan (12.3%) was significantly lower than for MPS (24.7%) or MUNIX (21.5%). All methods had ICC>0.94. MScan and Munix were significantly quicker to perform than MPS (6.3mvs. 13.2m). MScan (AUC=0.930) and MPS (AUC=0.899) were significantly better at discriminating between patients and healthy controls than MUNIX (AUC=0.831). CONCLUSIONS: MScan was more consistent than MPS or MUNIX and better at distinguishing ALS patients from healthy subjects. SIGNIFICANCE: MScan may improve detection and assessment of motor unit loss.

Modulation of the muscle and nerve compound muscle action potential by evoked pain.

Background and aims To our knowledge there are no studies that have examined the effects of the experimental pain on muscle fibre excitability as measured by the amplitudes of the potentials evoked by direct muscle stimulation (DMS) in a muscle at rest. We hypothesized that evoked pain can modulate the muscle compound action potential (CMAP) obtained by DMS possibly due to changes in muscle fibre excitability. Methods Pain was evoked by intramuscular infusion of hypertonic saline in 50 men. Ten control subjects were infused with isotonic saline. The infusions were given distal to the motor end plate region of the dominant brachial biceps muscle (BBM) in a double-blind manner. The nerve CMAP was obtained by stimulating the musculocutaneous nerve and recording from the BBM using surface-electrodes. Muscle CMAPs were obtained by direct muscle stimulation with subdermal electrodes placed subcutaneously in the distal third of the muscle. A stimuli-response curve of the amplitudes from muscle CMAP was obtained by stimulating from 10 to 90 mA. Results There was a decrease of the nerve CMAP amplitudes after infusion of isotonic saline (from 13.78mV to 12.16 mV), p-value 0.0007 and of hypertonic saline (from 13.35 mV to 10.85 mV), p-value 0.0000. The percent decrease from before to after infusion was larger in the hypertonic saline group (19.37%) compared to the isotonic saline group (12.18%), p-value 0.025. There was a decrease of the amplitudes of the muscle CMAP after infusion of both isotonic (at 90 mA from 13.84mV to 10.32 mV, p value 0.001) and of hypertonic saline (at 90 mA from 14.01 mV to 8.19 mV, p value 0.000). The percent decrease was larger in the hypertonic saline group compared to the isotonic saline group for all the stimulations intensities. At 90 mA we saw a 42% decrease in the hypertonic saline group and 24.5% in the isotonic saline group, p value 0.005. There were no changes in conduction velocity. Conclusion We found a larger amplitude decrease of the muscle and nerve potentials following hypertonic saline infusion compared with that of isotonic saline. We suggest that this deferential outcome of hypertonic saline on muscle CMAP may be linked to the nociceptive effect on muscle fibre membrane excitability. Implications The study supplies with some evidence of the peripheral effect of muscle pain. However, further trials with other nociceptive substances such as capsaicin should be performed.