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Clin Neurophysiol. 2018 Nov;129(11):2333-2340. doi: 10.1016/j.clinph.2018.08.025. Epub 2018 Sep 13.

The motor unit number index (MUNIX) profile of patients with adult spinal muscular atrophy.

Author information

1
Sorbonne Université, CNRS, INSERM, Laboratoire d'Imagerie Biomédicale, Paris, France; APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France.
2
APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France; APHP, Hôpital Pitié-Salpêtriere, Service d'Explorations Fonctionnelles, Paris, France.
3
APHP, Centre de Référence Maladies Neuromusculaires Paris-Est, Institut de Myologie, Hôpital Pitié-Salpêtrière, Paris, France.
4
APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France.
5
APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France; Département de recherche en éthique, EA 1610: Etudes des sciences et techniques, Université Paris Sud/Paris Saclay, Paris, France.
6
Hôpital des Peupliers, Ramsay Générale de Santé, F-75013 Paris, France.
7
Neurology Department, Nord/Est/Ile de France Neuromuscular Center, Raymond-Poincaré Hospital, Garches, France; INSERM U1179, END-ICAP, Versailles Saint-Quentin-en-Yvelines University, Montigny-le-Bretonneux, France.
8
Institut pour la Recherche sur la Moelle Epinière et l'Encéphale (IRME), Paris, France.
9
Sorbonne Université, CNRS, INSERM, Laboratoire d'Imagerie Biomédicale, Paris, France.
10
Sorbonne Université, CNRS, INSERM, Laboratoire d'Imagerie Biomédicale, Paris, France; APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France; Computational Neuroimaging Group, Academic Unit of Neurology, Trinity College Dublin, Ireland.
11
Institute of Myology, Neuromuscular Investigation Center, Paris, France; Institut pour la Recherche sur la Moelle Epinière et l'Encéphale (IRME), Paris, France.
12
Sorbonne Université, CNRS, INSERM, Laboratoire d'Imagerie Biomédicale, Paris, France; APHP, Département de Neurologie, Hôpital Pitié-Salpêtrière, Centre référent SLA, Paris, France; Northern Ireland Centre for Stratified Medicine, Biomedical Sciences Research Institute Ulster University, C-TRIC, Altnagelvin Hospital, Derry/Londonderry, United Kingdom. Electronic address: pierre-francois.pradat@psl.aphp.fr.

Abstract

OBJECTIVE:

Objective of this study is the comprehensive characterisation of motor unit (MU) loss in type III and IV Spinal Muscular Atrophy (SMA) using motor unit number index (MUNIX), and evaluation of compensatory mechanisms based on MU size indices (MUSIX).

METHODS:

Nineteen type III and IV SMA patients and 16 gender- and age-matched healthy controls were recruited. Neuromuscular performance was evaluated by muscle strength testing and functional scales. Compound motor action potential (CMAP), MUNIX and MUSIX were studied in the abductor pollicis brevis (APB), abductor digiti minimi (ADM), deltoid, tibialis anterior and trapezius muscles. A composite MUNIX score was also calculated.

RESULTS:

SMA patients exhibited significantly reduced MUNIX values (p < 0.05) in all muscles, while MUSIX was increased, suggesting active re-innervation. Significant correlations were identified between MUNIX/MUSIX and muscle strength. Similarly, composite MUNIX scores correlated with disability scores. Interestingly, in SMA patients MUNIX was much lower in the ADM than in the ABP, a pattern which is distinctly different from that observed in Amyotrophic Lateral Sclerosis.

CONCLUSIONS:

MUNIX is a sensitive measure of MU loss in adult forms of SMA and correlates with disability.

SIGNIFICANCE:

MUNIX evaluation is a promising candidate biomarker for longitudinal studies and pharmacological trials in adult SMA patients.

KEYWORDS:

Biomarkers; MUNIX; MUSIX; Motor unit loss; SMA type III; SMA type IV

PMID:
30248623
DOI:
10.1016/j.clinph.2018.08.025
[Indexed for MEDLINE]

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