Diaphragm paralysis occurs when the diaphragm, the primary muscle responsible for breathing, loses its ability to contract effectively. This large, dome-shaped muscle separates the chest and abdominal cavities and is solely controlled by the phrenic nerve. When the diaphragm contracts, it moves downward, creating negative pressure that draws air into the lungs. Paralysis results from an interruption of the signal transmission between the brain and the muscle, leading to a significant reduction in lung capacity. This dysfunction can be unilateral or bilateral, with the underlying cause dictating the extent and severity of the condition.
Causes Involving Direct Phrenic Nerve Damage
The most common causes of diaphragm paralysis involve direct, localized damage to the phrenic nerve. This type of injury is frequently referred to as iatrogenic, meaning it is unintentionally caused by medical intervention. Cardiac bypass grafting surgery carries a risk of phrenic nerve injury, sometimes due to the use of icy slush for heart cooling, which can cause a temporary cold injury. The nerve’s proximity to the internal thoracic artery also makes it vulnerable during dissection for coronary artery bypass procedures.
Other thoracic and neck surgeries, such as those for lung cancer or on the esophagus, can inadvertently compromise the nerve through direct cutting, stretching, or thermal damage. Localized physical trauma or compression is often the culprit in unilateral paralysis. Blunt or penetrating trauma to the chest or neck, such as from motor vehicle accidents, can physically sever or bruise the nerve, immediately halting the signal transmission.
Compression of the nerve by surrounding masses represents another form of direct damage, often leading to a slower onset of paralysis. Malignant tumors, particularly lung cancer or mediastinal masses, may grow to invade or press upon the phrenic nerve. Enlarged lymph nodes near the nerve route can also exert sufficient pressure to disrupt the nerve’s electrical signaling, resulting in flaccid paralysis. This localized interruption prevents the motor signal from reaching the muscle fibers.
Causes Related to Systemic Neuromuscular Disease
Diaphragm paralysis can result from systemic diseases that affect the entire nervous system or the muscles themselves, rather than a localized injury. These conditions frequently lead to bilateral paralysis because the disease process is widespread. Amyotrophic Lateral Sclerosis (ALS) and other motor neuron diseases progressively destroy the nerve cells in the brain and spinal cord that send signals to the phrenic nerve. As these motor neurons die, the capacity to generate the signal needed for diaphragm contraction is lost, leading to respiratory failure.
Guillain-Barré Syndrome (GBS) is an autoimmune condition where the immune system attacks the myelin sheath, the protective covering of peripheral nerves, including the phrenic nerve. This demyelination severely slows or blocks nerve conduction, making GBS a frequent cause of acute respiratory muscle paralysis requiring ventilatory support. Similarly, high cervical spinal cord injuries, particularly those affecting the C3 through C5 vertebral levels, can directly damage the motor neuron cell bodies responsible for initiating the phrenic nerve signal.
Diseases that primarily affect the muscle tissue, known as myopathies, can cause diaphragm failure even if the nerve signal is intact. Muscular dystrophies, such as Duchenne or Becker, cause the diaphragm muscle fibers to progressively weaken and degenerate. Neuromuscular junction disorders, like myasthenia gravis, interfere with the chemical communication between the nerve ending and the muscle fiber, preventing the electrical impulse from triggering a contraction.
Other Less Frequent Etiologies
A substantial percentage of diaphragm paralysis cases are categorized as idiopathic, meaning the specific cause remains undetermined despite thorough investigation. Estimates for these cases range widely, sometimes accounting for up to 20% to 50% of diagnoses. Idiopathic cases are often presumed to be viral in origin, as spontaneous recovery suggests temporary inflammation or mild nerve damage.
Infectious agents can directly target and inflame the phrenic nerve, a condition called phrenic neuritis. Certain viruses, including Herpes Zoster or the West Nile virus, have been documented to cause inflammation, resulting in temporary or permanent paralysis. Lyme disease is another bacterial infection that can sometimes trigger neuropathy affecting the phrenic nerve.
Exposure to certain toxins or medications can also interfere with nerve function and contribute to paralysis. This includes environmental agents, heavy metals, or specific drugs that disrupt the electrical or chemical processes necessary for nerve impulse transmission. In these cases, the failure is often a functional disruption rather than a physical severance or systemic degeneration.