The majority of people who have CMT will not develop breathing problems. But for the few who do, the symptoms are the same as those seen in other neuromuscular diseases that can impact breathing. They are not unique to CMT and can vary widely in severity.
Common symptoms include shortness of breath, shallow breathing, difficulty lying flat, shortness of breath with exertion, a weak cough, and sleep-disordered breathing, which can include obstructive sleep apnea, central sleep apnea, and nocturnal hypopnea. Some people may also experience elevated carbon dioxide levels, especially during sleep.
Often, the earliest signs are difficulty taking a full breath, a gradual increase in shortness of breath, breathing that becomes shallow, feeling air-starved when lying flat, becoming easily winded with mild physical activity, and running out of air when speaking. A weak cough may develop because the muscles used for breathing are also the muscles used for coughing. Sleep-disordered breathing can occur at any time.
What Is Orthopnea?
Orthopnea is defined as shortness of breath when lying flat on your back (supine) and is often an early sign of CMT-induced breathing muscle weakness. When lying flat, the chest cavity must expand against gravity, and the diaphragm must move against the weight of the abdominal cavity. Weakened breathing muscles may not be strong enough to overcome these mechanical demands, leading to increased shortness of breath.
What Is Obstructive Sleep Apnea?
Research suggests that CMT may predispose to obstructive sleep apnea (OSA). OSA occurs when the upper airway collapses during sleep, resulting in airway obstruction. Breathing pauses briefly (apnea) until the airway reopens. A person with CMT can have OSA with or without breathing muscle weakness, and OSA can be an early sign of breathing muscle involvement.
What Is Central Sleep Apnea?
Central sleep apnea (CSA) is different from OSA. In CSA, the airway remains open but breathing pauses because the signal from the brain to breathe briefly stops. A person with CMT can have both OSA and CSA. If the events are frequent or prolonged, oxygen levels may become reduced during sleep, even though lung tissue remains healthy.
What Is Nocturnal Hypopnea?
Nocturnal hypopnea is a period of rapid, shallow breathing during sleep that lasts at least ten seconds. This pattern leads to reduced lung inflation, which can lower oxygen levels and raise carbon dioxide levels. Hypopnea is often most noticeable during REM sleep. During REM, most breathing muscles are inactive except the diaphragm and the parasternal intercostals. If these muscles are weakened, they may not be able to fully support the respiratory demands required during REM, leading to hypopnea.
What Is Dyspnea on Exertion?
Dyspnea on exertion is shortness of breath that worsens with physical activity. During physical exertion, the body requires an increase in tidal volume (VT), which is the amount of air moved with each respiratory cycle (one breath in and out). Increasing VT depends on greater chest expansion. When the breathing muscles are weakened, the ability to increase chest expansion and, therefore, VT may be reduced, leading to a feeling of air hunger during physical activity.
Can CMT Cause Elevated Carbon Dioxide Levels?
One of the biggest concerns in CMT-related respiratory muscle weakness is the potential for elevated carbon dioxide (CO₂) levels, also known as hypercapnia. This occurs when the lungs cannot inflate enough to allow a full exchange of air. If the lungs do not fill with enough air, the body cannot blow out enough carbon dioxide, and CO₂ is pulled back into the bloodstream on the next breath.
Symptoms of hypercapnia can include headaches, confusion, difficulty staying awake, and worsening shortness of breath. Therefore, managing CO2 levels is a primary focus in treating CMT-related breathing issues.
Can CMT Cause Low Oxygen Levels?
Oxygen levels are usually normal in CMT-related respiratory muscle weakness because lung tissue remains unaffected. The lungs can still effectively pull oxygen into the body. When oxygen levels do reduce, it is usually due to sleep-disordered breathing. Once awake and upright, oxygen levels typically return to normal.
Talk to Your Healthcare Provider
This is not a complete list. If you are experiencing any respiratory symptoms, CMT might not be the cause. It is important to discuss your symptoms with a qualified healthcare provider and follow their guidance.
