B.Faurouxa,b, L.Griffona,b, A.Amaddeoa,b, N.Stremlerc, J.Mazenqc, S.Khirania,b,d, M.Baravalle-Einaudic.
ABSTRACT
Spinal muscular atrophy (SMA) causes a predominantly bilateral proximal muscle weakness and atrophy. The respiratory muscles are also involved with a weakness of the intercostal muscles and a relatively spared diaphragm. This respiratory muscle weakness translates into a cough impairment, resulting in poor clearance of airway secretions and recurrent pulmonary infections, restrictive lung disease due to a poor or insufficient chest wall and lung growth, nocturnal hypoventilation and, finally, respiratory failure. Systematic and regular monitoring of respiratory muscle performance is necessary in children with SMA in order to anticipate respiratory complications, such as acute and chronic respiratory failure, and guide clinical care. This monitoring is based in clinical practice on volitional and noninvasive tests, such as vital capacity, sniff nasal inspiratory pressure, maximal static pressures, peak expiratory flow and peak cough flow because of their simplicity, availability and ease. In young children, those with poor cooperation or severe respiratory muscle weakness, other, mostly invasive, tests may be required to evaluate respiratory muscle performance. A sleep study, or at least overnight monitoring of nocturnal gas exchange is mandatory for detecting nocturnal alveolar hypoventilation. Training for patients and caregivers in cough-assisted techniques is recommended when respiratory muscle strength falls below 50% of predicted or in case of recurrent or severe respiratory infections. Noninvasive ventilation (NIV) should be initiated in case of isolated nocturnal hypoventilation and followed by a pediatric respiratory team with expertise in NIV. Multidisciplinary (neurology and respiratory) pediatric management is crucial for optimal care of children with SMA.
© 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
Spinal muscular atrophy (SMA) is a common genetic neuromuscular disease involving the motor neurons. The incidence of SMA is estimated to be 1 in 6,000 to 1 in 10,000 live births. SMA represents the second most common cause of mortality from a recessive genetic disorder and children with SMA are among the weakest patients with neuromuscular disorders (NMD). Due to the wide disease presentation, patients are classified in 3 types (type I-III), based on the onset age, the severity of disease and...
2. Respiratory muscle involvement in children with SMA and its consequences
In healthy individuals, inspiration is characterised by a synchronous expansion of the thorax and the abdomen, due to a simultaneous contraction of the diaphragm, which is the main inspiratory muscle, and the external intercostal muscles which contribute to the expansion of the rib cage. Analysis of the respiratory muscles in SMA has shown that the strength of the diaphragm is relatively well preserved, with a predominant weakness of the intercostal muscles. Thus, inspiration relies mainly on...
3.1. Which tests can be used to monitor respiratory muscle strength in children with SMA?
The assessment of the respiratory muscles is challenging because these muscles are not directly accessible as is the case for peripheral muscles. As the function of muscles is to develop force and shorten, in the respiratory system, force is generally estimated as pressure and shortening as lung volume change or displacement of chest wall structures. Tests evaluating respiratory muscles are separated in “volitional” or “nonvolitional” tests and “noninvasive” or “invasive” tests (i.e. requiring...
4. Management of respiratory muscle weakness in children with SMA
The aim of respiratory monitoring is to anticipate respiratory complications by guiding clinical care. Few studies have tried to identify respiratory parameters associated with the risk of respiratory infection or sleep-disordered breathing in children with NMD. Inspiratory VC, PCF and Peak Expiratory Pressure were shown to correlate negatively with the number of chest infections and the number of days treated with antibiotics in a group of 46 children and adolescents with various NMD [13]. The...
5. Conclusion
Respiratory involvement plays a major role in morbidity and mortality in children with SMA. Optimal respiratory care requires multidisciplinary pediatric care including neurologists, pulmonologists, physiotherapists and an experienced home NIV team when NIV becomes necessary. A systematic and regular evaluation of the respiratory muscle function is crucial for the prevention and effective management of respiratory complications in these children.
Disclosure of interest
The authors declare that they have no conflict of interest with this review.
Authorship
Brigitte Fauroux is the main author of the manuscript. Melisande Baravalle, Lucie Griffon, Alessandro Amaddeo, Nathalie Stremler, Julie Mazenq, and Sonia Khirani, contributed to the management of the children with SMA followed in our centers and the writing of the manuscript. All the authors approved the final version of the manuscript.
Funding
This review was performed without funding.
Acknowledgements
The research of Brigitte Fauroux is supported by is supported by the Association Française contre les Myopathies (AFM), Assistance Publique-Hôpitaux de Paris, Paris University, ASV Santé, ADEP Assistance, and ASTEN Santé.
This article is part of a supplement entitled Infantile Spinal Muscular Atrophy (SMA) Diagnosis and Management published with institutional support from Biogen.