Current Series: Advances in the Treatment of Spinal Muscular Atrophy

Crystal Proud, MD: That was a nice discussion of diagnosis and symptoms of spinal muscular atrophy [SMA]. Let's transition now to discussing more of the nonpharmacologic management of spinal muscular atrophy. SMA is a diagnosis that leads to progressive motor neuron deterioration and resultant muscle weakness. This impacts muscles throughout the body, including those of the arms and legs, muscles that permit swallowing and speech, as well as those that support respiration. As you can imagine, we may have a variety of different subspecialists and individuals who provide supportive care as members of our team, caring for our patients impacted by this diagnosis. Nancy, I was hoping that you could review the pulmonary care that's required for our patients with SMA. 
 
Nancy L. Kuntz, MD
: Absolutely. Children who have spinal muscular atrophy, or even older children with spinal muscular atrophy, have primarily a decreased ventilation, a decreased volume, a decreased strength of the breathing. In addition, they have decreased power for cough and airway clearance. I think that from very early in the course all the way through the course of spinal muscular atrophy, those 2 issues, providing ventilation and providing airway clearance, are things that need to be monitored.  
 
You heard mentioned that, with the older children, some of the outcome measures that can be followed are pulmonary functions, but those are things that can't be easily measured in children until they are 5 to 6 years old because they don't quite catch the gist of the test to do it reliably and accurately before then. What we do in the younger children is monitor things first clinically, looking to see if there is evidence of the paradoxical or abdominal breathing that I think you heard John mention.  
 
He mentioned the paraspinal or the intercostal muscles provided by the paraspinal muscles being relatively weak, with most of the air movement occurring because of contraction of the relatively spared diaphragm. What this does is that, with inspiration, instead of the chest wall expanding and the chest going up, what happens is that the diaphragm pushes down and pushes the abdomen up. You have the abdomen being protuberant during inspiration, and that’s a clinical sign of spinal muscular atrophy. 
 
When we note that in children, that's when people begin to take special measures. It's becoming increasingly easier to monitor CO2 [carbon dioxide] and transcutaneous CO2, but it's still not as readily available as oxygen levels. One of the things that people will frequently do if there's a question that the respiratory muscles are beginning to fail in a clinically important way, would be to look at the baby’s sleep because, obviously, everyone breathes a little more shallowly during sleep. That would be the first place that distress or insufficiency will occur in a patient with spinal muscular atrophy.  
 
Doing an overnight polysomnogram to look at the adequacy of the sleep is something that’s very important. That can be remediated by positive pressure ventilation. It's important that BiPAP [bilevel positive airway pressure] be considered, and there are a lot of noninvasive ways with nasal pillows, facemasks, or other things that can be used and monitored over time for children. It is a different issue to have neuromuscular respiratory weakness than most of the respiratory insufficiency that occurs in children. I see this in our ICU [intensive care unit] when children have very bad respiratory viruses. 
 
Some of the temptation is to put a child on high-flow oxygen or oxygen of any sort because, many times when children have bronchiolitis or other things like that, that's very helpful to them. But that does not help children for whom the primary problem is that the volume of air moving is insufficient. What you need there is the pressure or the breathing, and it’s relatively uncommon that the children need oxygen. It certainly isn't the first step.  
 
Ventilation or support for the weak respiratory muscles is one thing that's monitored. Something that more of us will encounter over time and then perhaps less as the children get treated earlier is the question of whether preventive measures should be taken when children have spinal muscular atrophy to expand the chest wall during the period of rapid growth during infancy. John mentioned that there is  this bell-shaped chest, which is narrow on the top and wider on the bottom.  
 
This is something happens because, over time, the chest wall does not expand, so it grows in the position in which it tends to spend most of its time, which is narrow on the top. Some clinicians have found that early institution of positive pressure, even just during sleep, allows a good chest wall expansion and a more normal volume of the chest wall and therefore normal shape as it proceeds over time. That would be an early option to see in place, almost as a preventive measure. 
 
The second issue I brought up was airway clearance, and pulmonologists within pediatrics have done a wonderful job bringing cough assist, something called insufflator-exsufflator. It's something that puts in a certain amount of premeasured, specified pressure, and then withdraws it with a mask. What that does is it shakes up or clears secretions so that, with whatever degree of cough people have, or postural drainage, or whatever else, the secretions can be cleared from the airway much better. 
 
This is something that is usually for anyone who has a degree of respiratory weakness instituted early and practiced so it doesn't appear awkward or weird either to the family as a caregiver or the child. And then, it is usually not done very often, maybe once a day just for practice and to keep the machine available and familiar. It is then increased if there is any respiratory distress due to a respiratory illness. 
 
I have been very impressed that this, as a tool for families, has been something that's kept many of my patients out of the hospital during intercurrent respiratory illnesses, and that's always a wonderful thing because, even if there isn't a pandemic going on, during most winter seasons and springs in the Midwest, we have enough respiratory viruses of various sorts that are of an increased risk to children who have respiratory weakness. You’d really rather they weather out whatever they have if they can, safely at home, and not come into the ICU and get exposed to more. 
 
Crystal Proud, MD: Absolutely. Pulmonary health obviously plays an incredible role in the care of our patients.