Assessment of the reliability of the motor unit size index (MUSIX) in single subject “round-robin” and multi-centre settings

Objective The motor unit size index (MUSIX) is incorporated into the motor unit number index (MUNIX). Our objective was to assess the intra-/inter-rater reliability of MUSIX in healthy volunteers across single subject “round robin” and multi-centre settings. Methods Data were obtained from i). a round-robin assessment in which 12 raters (6 with prior experience and 6 without) assessed six muscles (abductor pollicis brevis, abductor digiti minimi, biceps brachii, tibialis anterior, extensor digitorum brevis and abductor hallucis) and ii). a multi-centre study with 6 centres studying the same muscles in 66 healthy volunteers. Intra/inter-rater data were provided by 5 centres, 1 centre provided only intra-rater data. Intra/inter-rater variability was assessed using the coefficient of variation (COV), Bland-Altman plots, bias and 95% limits of agreement. Results In the round-robin assessment intra-rater COVs for MUSIX ranged from 7.8% to 28.4%. Inter-rater variability was between 7.8% and 16.2%. Prior experience did not impact on MUSIX values. In the multi-centre study MUSIX was more consistent than the MUNIX. Abductor hallucis was the least reliable muscle. Conclusions The MUSIX is a reliable neurophysiological biomarker of reinnervation. Significance MUSIX could provide insights into the pathophysiology of a range of neuromuscular disorders, providing a quantitative biomarker of reinnervation

Retrospective diagnosis of congenital cytomegalovirus infection and cortical maldevelopment

Congenital cytomegalovirus (CMV) infection can cause malformations of cortical development (MCD). It is difficult to establish CMV as a cause of MCD several months postpartum. This can now be done by detection of CMV DNA in dried blood spots (DBS test) on Guthrie cards. The authors used DBS tests to assess 10 patients with MCD of unknown cause. Four of the 10 patients were positive for CMV

Reinnervation as measured by the motor unit size index is associated with preservation of muscle strength in amyotrophic lateral sclerosis but not all muscles reinnervate

Introduction The motor unit size index (MUSIX) may provide insight into reinnervation patterns in diseases such as amyotrophic lateral sclerosis (ALS). However, it is not known if MUSIX detects clinically relevant changes in reinnervation, or if all muscles manifest changes in MUSIX in response reinnervation following motor unit loss. Methods 57 patients with ALS were assessed at 3-monthly intervals for 12 months in 4 centres. Muscles examined were abductor pollicis brevis, abductor digiti minimi, biceps brachii and tibialis anterior. Results were split into two groups: muscles with increases in MUSIX and those without. Longitudinal changes in MUSIX, motor unit number index (MUNIX), compound muscle action potential (CMAP) amplitude and medical research council (MRC) strength score were investigated. Results 133 muscles were examined. 59% of muscles exhibited an increase in MUSIX during the study. Muscles with MUSIX increases lost more motor units (MUNIX decline at 12 months -58%, p<0.001) than muscles that did not increase MUSIX (MUNIX decline at 12 months -34.6%, P<0.001). Despite this, longitudinal changes in muscle strength were similar. When motor unit loss was similar, an absence of MUSIX increase was associated with a significantly greater loss of muscle strength (P = 0.002). Discussion MUSIX increases are associated with greater motor unit loss but relative preservation of muscle strength. Thus, MUSIX appears to be measuring a clinically relevant response that can provide a quantitative outcome measure of reinnervation in clinical trials. Furthermore, MUSIX suggests that reinnervation may play an important role in determining the progression of weakness

Motor Unit Number Index (MUNIX): reference values of five different muscles in healthy subjects from a multi-centre study.

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Motor Unit Number Index (MUNIX): a novel neurophysiological marker for neuromuscular disorders; test-retest reliability in healthy volunteers.

Item does not contain fulltextOBJECTIVE: To investigate the intra-rater and inter-rater test-retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting. METHODS: Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners. RESULTS: The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies. CONCLUSION: MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability. SIGNIFICANCE: Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.1 september 201

Motor Unit Number Index (MUNIX): a novel neurophysiological marker for neuromuscular disorders; test-retest reliability in healthy volunteers.

Item does not contain fulltextOBJECTIVE: To investigate the intra-rater and inter-rater test-retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting. METHODS: Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners. RESULTS: The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies. CONCLUSION: MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability. SIGNIFICANCE: Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.1 september 201