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Clin Neurophysiol. 2017 Mar;128(3):495-500. doi: 10.1016/j.clinph.2016.11.026. Epub 2016 Dec 18.

Motor Unit Number Index (MUNIX) detects motor neuron loss in pre-symptomatic muscles in Amyotrophic Lateral Sclerosis.

Author information

1
Neuromuscular Diseases Unit/ALS Clinic, Kantonsspital St. Gallen, St. Gallen, Switzerland. Electronic address: christoph.neuwirth@kssg.ch.
2
Medical College of Wisconsin, Milwaukee, WI, USA.
3
Neuromuscular Diseases Unit/ALS Clinic, Kantonsspital St. Gallen, St. Gallen, Switzerland.
4
Department of Neurosciences, Hospital de Santa Maria, Instituto de Medicina Molecular, Faculty of Medicine, University of Lisbon, Lisbon, Portugal.
5
Kantonsspital Winterthur, Winterthur, Switzerland.
6
Natus Medical Inc, Middleton, WI, USA.
7
Institute of Neurosciences, Uppsala University, Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden.
8
Neuromuscular Diseases Unit/ALS Clinic, Kantonsspital St. Gallen, St. Gallen, Switzerland; Department of Neurology, University Hospital Basel, Basel, Switzerland.

Abstract

OBJECTIVE:

Motor Unit Number Index (MUNIX) is a quantitative neurophysiological measure that provides an index of the number of lower motor neurons supplying a muscle. It reflects the loss of motor neurons in patients with Amyotrophic Lateral Sclerosis (ALS). However, it is unclear whether MUNIX also detects motor unit loss in strong, non-wasted muscles.

METHODS:

Three centres measured MUNIX in 49 ALS patients every three months in six different muscles (abductor pollicis brevis, abductor digiti minimi, biceps brachii, tibialis anterior, extensor digitorum brevis, abductor hallucis) on the less affected side. The decline of MUNIX in initially non-wasted, clinically strong muscles (manual muscle testing, MMT grade 5) was analysed before and after onset of weakness.

RESULTS:

In 49 subjects, 151 clinically strong muscles developed weakness and were included for analysis. The average monthly relative loss of MUNIX was 5.0% before and 5.6% after onset of weakness. This rate of change was significantly higher compared to ALS functional rating scale (ALSFRS-R) and compound muscle action potential (CMAP) change over 12months prior to the onset of muscle weakness (p=0.024).

CONCLUSION:

MUNIX is an electrophysiological marker that detects lower motor neuron loss in ALS, before clinical weakness becomes apparent by manual muscle testing.

SIGNIFICANCE:

This makes MUNIX a good biomarker candidate for disease progression and possibly pharmacodynamics responds.

KEYWORDS:

ALSFRS-R; Biomarker; MUNIX; Multicentre; Pre-symptomatic ALS

Comment in

PMID:
28043769
DOI:
10.1016/j.clinph.2016.11.026
[Indexed for MEDLINE]

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