Cough, sniff and maximal static pressure patterns in spinal muscular atrophy

Management of Spinal Muscular Atrophy in the Adult Population

Spinal muscular atrophy (SMA) is a group of neurodegenerative disorders resulting from the loss of spinal motor neurons. 95% of patients share a pathogenic mechanism of loss of survival motor neuron (SMN) 1 protein expression due to homozygous deletions or other mutations of the SMN1 gene, with the different phenotypes influenced by variable copy numbers of the SMN2 gene. Advances in supportive care, disease modifying treatment and novel gene therapies have led to an increase in the prevalence of SMA, with a third of SMA patients now represented by adults. Despite the growing number of adult patients, consensus on the management of SMA has focused primarily on the pediatric population. As the disease burden is vastly different in adult SMA, an approach to treatment must be tailored to their unique needs. This review will focus on the management of the adult SMA patient as they age and will discuss proper transition of care from a pediatric to adult center, including the need for continued monitoring for osteoporosis, scoliosis, malnutrition, and declining mobility and functioning. As in the pediatric population, multidisciplinary care remains the best approach to the management of adult SMA. Novel and emerging therapies such as nusinersen and risdiplam provide hope for these patients, though these medications are of uncertain efficacy in this population and require additional study.

Effect of nusinersen on respiratory function in paediatric spinal muscular atrophy types 1-3

INTRODUCTION

Nusinersen is used in spinal muscular atrophy (SMA) to improve peripheral muscle function; however, respiratory effects are largely unknown.

AIM

To assess the effects of nusinersen on respiratory function in paediatric SMA during first year of treatment.

METHODS

A prospective observational study in paediatric patients with SMA who began receiving nusinersen in Queensland, Australia, from June 2018 to December 2019. Outcomes assessed were the age-appropriate respiratory investigations: spirometry, oscillometry, sniff nasal inspiratory pressure, mean inspiratory pressure, mean expiratory pressure, lung clearance index, as well as polysomnography (PSG) and muscle function testing. Lung function was collected retrospectively for up to 2 years prior to nusinersen initiation. Change in lung function was assessed using mixed effects linear regression models, while PSG and muscle function were compared using the Wilcoxon signed-rank test.

RESULTS

Twenty-eight patients (15 male, aged 0.08-18.58 years) were enrolled: type 1 (n=7); type 2 (n=12); type 3 (n=9). The annual rate of decline in FVC z-score prior to nusinersen initiation was -0.58 (95% CI -0.75 to -0.41), and post initiation was -0.25 (95% CI -0.46 to -0.03), with a significant difference in rate of decline (0.33 (95% CI 0.02 to 0.66) (p=0.04)). Most lung function measures were largely unchanged in the year post nusinersen initiation. The total Apnoea-Hypopnoea Index (AHI) was reduced from a median of 5.5 events/hour (IQR 2.1-10.1) at initiation to 2.7 events/hour (IQR 0.7-5.3) after 1 year (p=0.02). All SMA type 1% and 75% of SMA types 2 and 3 had pre-defined peripheral muscle response to nusinersen.

CONCLUSION

The first year of nusinersen treatment saw reduced lung function decline (especially in type 2) and improvement in AHI.

Respiratory management of children with spinal muscular atrophy (SMA)

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.