Respiratory complications are among the most serious concerns associated with spinal muscular atrophy (SMA) and are the leading cause of morbidity and mortality in these patients. Effective management requires the close monitoring of respiratory function and the timely implementation of supportive interventions.

The pulmonary aspects of SMA are a cornerstone of its management. The inability to breathe well can be life-limiting for some patients with SMA, and respiratory failure is often the cause of death among those with the disorder. If a patient is in chronic respiratory failure, an acute stressor can be fatal. There are various levels of the kind of respiratory support that may be needed. For example, walkers with SMA typically do not need significant breathing support while nonsitters with SMA almost universally will need respiratory support. The entire spectrum is highly variable, ranging from newborns who are diagnosed early via newborn screening and may have minimal symptoms, receive treatment quickly, and are doing very well, to those who had SMA for a long time before disease-modifying therapy (DMT) was available and now need significant respiratory support as teenagers or adults living with SMA.

A basic truth about SMA is that there is a phase of the disease that relentlessly progresses and gets worse, no matter when a patient is diagnosed with symptoms. What we are trying to do with DMTs is to stabilize the patient to a higher level of improvement before reaching a plateau in function and to subsequently progress at a slower rate of decline than would have occurred in the natural history of the disease. Patients with SMA who would never have sat in their natural history may now become sitters because they have had the support of an intervention that gives them back some SMN protein. These individuals may experience an altered long-term trajectory, with a different type of scoliosis, contractures, and response to stressors such as fractures or viral illnesses. In addition, we may see more resilience in patients on DMT when they have a stressor such as a viral infection, as DMT may lead to fewer infections in general in individuals on treatment and potentially shorter stays in the hospital (if they do happen), with less intervention needed than in the past. These are all encouraging trends that we are seeing in some of the real-world data.

Proactive (rather than reactive) pulmonary care is important. However, oversupporting patients with SMA is also a risk. So, it is important to tailor the intervention to the individual in terms of where they are in their own developmental trajectory, taking into account their lifestyle to ensure the best quality of life while preventing complications such as acute-on-chronic respiratory failure.

The most severe forms of SMA unfortunately remain the most common, so, in this new age of newborn screening identification and early diagnosis, we want to be vigilant in those with early, rapidly progressing symptoms. The challenge is that pulmonary function tests are unreliable before approximately age 6 years, so other indicators, such as sleep studies, response to viral illnesses, and family observations on sleep or breathing even while awake, are important indicators to identify those who need to be watched more closely and be put on appropriate supportive interventions. A patient’s bulbar function is also important to consider, including their swallowing ability and eating choices. Nutritionists, gastroenterologists, and speech therapists need to be involved, especially if swallowing is significantly affected, as respiratory status can fluctuate based on swallowing health.

Puberty can present additional challenges, especially for sitters. Often, the growth around that period can change the dynamics of movement in general and can affect the progression of scoliosis, which can impact respiratory function. Even in patients on DMTs, scoliosis remains prevalent and requires monitoring via x-ray. Bracing may help stabilize progression, but severe cases require surgery, such as spinal fusion or growth rod surgery. Spinal surgery itself affects respiratory function. Therefore, it is critical to keep an eye on the patient’s scoliotic curve in conjunction with our orthopedic colleagues.