One-third of adults with SMA show signs of poor lung function
About a third of adults with spinal muscular atrophy (SMA) show signs of poor, and abnormal, lung function, according to new analyses that found breathing problems were more likely in patients with severe disease — including those with type 2 SMA and those without an ability to walk.
Lower lung function among these SMA patients also was tied to a increased need for noninvasive ventilation (NIV) and scoliosis surgery, and to worse motor function, the researchers found.
“Respiratory function in adult SMA patients is relatively frequently impaired, substantially stable, and significantly correlated with motor function and disease severity,” the team wrote, noting that “disease duration and age do not correlate with respiratory dysfunction.”
The researchers called for further study “focusing in particular on older patients” and those with more severe disease types.
Their findings were detailed in “Respiratory function in a large cohort of treatment-naïve adult spinal muscular atrophy patients: a cross-sectional study,” published in Neuromuscular Disorders.
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Guidelines call for breathing checks only in adults with poor lung function
In SMA, weakness in the muscles needed for breathing can cause respiratory dysfunction, which correlates with SMA type. Patients with more severe SMA — specifically types 1 or 2 — are more likely to experience significant breathing issues compared with individuals with less severe disease, typically types 3 or 4.
International guidelines recommend that SMA patients who have the ability to sit up or walk should undergo breathing assessments only if there is clinical evidence of respiratory dysfunction.
Further, noninvasive ventilation for breathing support — in some cases provided by a BiPAP or bi-level positive pressure machine — is only recommended for patients who cannot walk. A BiPAP machine, worn as a mask over the nose and mouth, or as a tube to the nose, can make breathing easier by changing the pressure of air during inhalation and exhalation.
These guidelines, however, are largely based on pediatric patients, because there is a lack of lung function data for adults with SMA.
“Indeed, life-long follow-up and respiratory care in adult patients are not specifically addressed in guidelines or recommendations,” the researchers noted.
Now, a team of scientists from across Italy aimed to learn more about respiratory function in SMA patients in the country. They evaluated lung function among 145 treatment-naïve adults with SMA in Italy. The patients, 40% of whom were women, had a median age of 37 and had been living with SMA for a median of 29.7 years.
Among the patients were 18 with SMA type 2, 125 with SMA type 3, and two with SMA type 4. A total of 66 were able to walk. The 79 people considered sitters had lost their walking ability at a median age of 18.
Lung function was evaluated with the forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) tests. FVC is a measure of the amount of air one can forcibly exhale from the lungs in a single exhalation, while FEV1 measures the amount of air a person can force out of the lungs in one second.
The median FVC value was 88% of what’s predicted based on age and sex. Median FEV1 performance was 90.5%.
Lung function was significantly higher for people with SMA type 3 versus type 2. For those with type 3, individuals who retained their walking ability had better lung function than did patients who had not.
Generally speaking, lower FVC and FEV1 values were found to be significantly associated with indicators of more severe disease, including SMA type 2, fewer copies of the so-called backup SMN2 gene, and a loss of walking ability. Age was associated with lung function only among SMA type 3 walkers.
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Patients with poor lung function more likely to need noninvasive ventilation
About a third of patients were found to have abnormal FVC (37%) or FEV1 (31%) performance — meaning less than 80% of the expected value. Abnormal FVC values were significantly more represented in SMA2 patients.
NIV was needed in 21 patients (14.6%) for respiratory issues, which started at a median age of 23. The need for NIV was significantly linked to lower lung function values. Moreover, NIV was started at a significantly younger age in SMA2 patients than in SMA3 sitters or walkers.
A number of other clinical factors were tied to impaired respiratory function. Specifically, patients with lower lung FVC and FEV1 values also were more likely to need cough assistance or surgery for scoliosis. These individuals also had worse motor function and were more likely to see a loss of walking ability.
Further, the need for NIV and surgery for scoliosis were significantly more frequent in those with SMA2 but were not correlated to each other.
Respiratory function should be regularly followed-up in adult patients with SMA, regardless the disease severity.
This work highlights the need for better management of respiratory problems in both adult and pediatric SMA patients, the researchers said, calling it a focus “of outmost importance.”
They noted that “respiratory dysfunction can cause significant morbidity and mortality, mainly because of a higher risk of respiratory infections.”
“Overall, respiratory function should be regularly followed-up in adult patients with SMA, regardless the disease severity,” the researchers wrote, noting that these measurements can ultimately serve as biomarkers for monitoring treatment responses.
The team did note that “respiratory function appears to stabilize in adulthood, except for [among] walking patients.”
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