Complications of Spinal Muscular Atrophy: Respiratory Problems

Reviewed by: HU Medical Review Board | Last reviewed: August 2021

People with spinal muscular atrophy (SMA) have weaker chest muscles because of a problem with their motor neurons. In severe types of SMA, progressive chest weakness leads to breathing problems. Respiratory failure is a leading cause of illness and death for people with SMA types 1 and 2.1,2

Respiratory support is essential for children with SMA to survive and be comfortable. This includes monitoring lung function, airway clearance, and breathing support. The techniques used depend on the type of SMA, the severity of symptoms, and acute events like colds and surgeries.1,2

What respiratory problems do people with SMA experience?

Children with SMA can experience many respiratory problems, including:1

  • Underdeveloped lungs
  • Weak cough, which can cause mucus to stay in the lungs
  • Higher risk of lung infections (pneumonia)
  • More severe reactions to viral infections, such as respiratory syncytial virus (RSV)
  • Swallowing problems and risk of inhaling food or liquid into the lungs (aspiration)
  • Shallow or slow breathing during sleep (hypoventilation)

These respiratory problems often lead to respiratory failure. This happens when the lungs do not give blood enough oxygen. Respiratory failure can be a medical emergency. It is a common cause of death for children with SMA.2

Scoliosis (spine curvature) can also contribute to respiratory problems and can cause restrictive lung disease. This happens when the lungs do not have space to take in enough air.3

Why does spinal muscular atrophy cause respiratory problems?

Normally, we breathe using 2 muscle groups: intercostal muscles and the diaphragm. The intercostal muscles are between the rib cage and help it expand outward as the lungs inflate. The diaphragm is a muscle below the rib cage that helps it expand downward when lungs inflate.1

Children with SMA breathe differently because of weak intercostal muscles. Their diaphragms are stronger and become the main breathing muscle. The rib cage does not expand outward during breathing but still gets pulled downward. This causes “stomach breathing” because the stomach expands instead of the chest. Stomach breathing can cause children with SMA to have bell-shaped chests or sunken chests.1

How are these issues prevented and treated?

Children with SMA types 1 and 2 should be monitored every few months for breathing problems. People with type 3 SMA should also be regularly monitored, but less often. In these evaluations, doctors may monitor:4

  • Coughing and swallowing ability
  • Oxygen levels in the blood using pulse oximetry
  • Changes in the chest wall
  • Breathing ability during sleep
  • Scoliosis (spine curvature)

Breathing exercises may help improve the ability to inflate the lungs. Children can use a cough machine or a resuscitator bag and mask to provide air as they inhale. Cough machines also improve coughing and airway clearance. Other techniques used by doctors and caretakers to clear airways include:1,4

  • Manual cough assistance – Putting upward pressure on the abdomen during coughing
  • Chest physiotherapy – Methods using hands or devices to loosen mucus
  • Postural drainage – Positioning children at an incline with head and chest lower than the legs
  • Intrapulmonary percussive ventilation (IPV) – A machine that provides air pressure into the lungs to loosen secretions

Children with SMA benefit from proactive breathing support. During colds, most children with severe types of SMA will need extra support. Before or after surgery, children with SMA may also need support.4,5

The technique used depends on the severity and how long support is needed. Children may need breathing support 24 hours a day or only while asleep. To help children breathe during sleep, doctors may use:4,5

  • Bi-level Positive Airway Pressure (BiPAP) – A machine that provides air at a rate depending on the child’s breathing and sleep cycle
  • Mechanical ventilator – A machine with more options and settings to control breathing better
  • Negative pressure ventilator (NPV) – A machine encircling the chest with a vacuum to expand the chest and bring air into the lungs

Continuous positive airway pressure (CPAP) gives one continuous air pressure or amount of air. Children with SMA should not use CPAP because it may not allow breathing muscles to relax enough.5

Breathing support can either be “non-invasive” or “invasive.” Non-invasive ventilation (NIV) uses devices outside of the body, such as a face mask, connected to the ventilator to help with breathing. Invasive ventilation uses devices inside the body, with a ventilator connected through a breathing tube into the mouth or body.1,3

Decisions about respiratory support become difficult if non-invasive methods are not enough to support breathing long-term. Stopping interventions, transitioning to palliative (comfort-focused) care, or maintaining long-term invasive ventilation is a deeply personal decision.

All loving and caring parents make different choices, and there is no right choice to make. Ask your doctor about the advantages of each technique for your child. Make a plan of action with your doctor for future changes. This can help act quickly in case of an emergency.1

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