Diaphragm paralysis occurs when the diaphragm, the main muscle responsible for breathing, loses its ability to contract effectively. This large, dome-shaped sheet of muscle is situated at the base of the chest cavity, separating it from the abdomen. Normally, when a person inhales, the diaphragm contracts and moves downward, increasing chest volume and drawing air into the lungs. Paralysis, which can affect one side (unilateral) or both sides (bilateral), disrupts this mechanical process, significantly reducing lung capacity. When the diaphragm is paralyzed, accessory muscles must compensate, leading to symptoms like shortness of breath, especially when lying flat or during physical exertion. Causes generally fall into three categories: damage to the controlling nerve, systemic diseases affecting the nervous system, or injury to the muscle itself.
Local Injury to the Phrenic Nerve
The phrenic nerve is the sole nerve responsible for controlling the movement of the diaphragm, originating from the cervical spine in the neck at the C3, C4, and C5 levels. Because of its long path from the neck down through the chest cavity to the diaphragm, it is vulnerable to localized damage or compression at various points along its route. Damage to this nerve is the most common cause of diaphragm paralysis.
Iatrogenic injury, damage caused unintentionally by a medical procedure, is a frequent cause, particularly following cardiothoracic or cervical surgeries. Procedures near the heart, such as cardiac bypass grafting, carry a risk of phrenic nerve injury.
Other surgical procedures, including those involving the neck, esophagus, or chest cavity, also place the phrenic nerve at risk of being cut, stretched, or traumatized. Furthermore, certain nerve blocks used for pain control, such as interscalene or high thoracic blocks, may result in the local anesthetic spreading to and temporarily blocking the function of the phrenic nerve. This chemical block interrupts the electrical signal, causing a temporary, reversible paralysis of the corresponding side of the diaphragm.
The phrenic nerve can also be damaged by blunt or penetrating physical trauma to the neck or chest. A sudden, forceful impact to the neck, such as a sports injury or motor vehicle accident, can bruise, stretch, or even tear the nerve fibers. Similarly, penetrating injuries from stab or gunshot wounds to the chest can sever the nerve, leading to permanent paralysis on that side.
Compression of the nerve by nearby growths or masses is another mechanism of local injury. Tumors, such as lung cancers or cancers in the mediastinum, can grow directly into or press against the phrenic nerve, physically preventing it from transmitting signals. Non-cancerous masses like cysts or enlarged lymph nodes can also exert compressive force, functionally blocking the nerve’s ability to stimulate the diaphragm.
Systemic Neurological and Infectious Conditions
Diaphragm paralysis can arise as a symptom of a body-wide disease that affects the nervous system or the neuromuscular junction. These systemic conditions disrupt the communication pathway between the brain and the diaphragm, often affecting other muscles in the body as well. Neurological diseases that progressively destroy nerve cells are a notable cause, including motor neuron diseases like Amyotrophic Lateral Sclerosis (ALS). In ALS, the motor neurons supplying the phrenic nerve degenerate, leading to progressive muscle weakness and eventual paralysis.
Autoimmune disorders are another significant category. Guillain-Barré Syndrome (GBS) is a prime example, where the immune system attacks the myelin sheath surrounding peripheral nerves, including the phrenic nerve. This damage slows or halts the nerve’s ability to conduct electrical impulses, causing rapid onset of muscle weakness.
Infectious agents can also trigger nerve damage that results in diaphragm paralysis. Certain viruses and bacteria can directly invade or provoke an immune response against the nervous system, a process known as neuropathy. For instance, Lyme disease or the Varicella-Zoster virus (which causes shingles) have been linked to inflammation and damage of the phrenic nerve.
Other conditions that cause widespread nerve damage, or polyneuropathies, can affect the diaphragm. These include uncontrolled diabetes, which can lead to diabetic neuropathy, or chronic inflammatory demyelinating polyneuropathy (CIDP). These systemic processes interfere with the proper electrical signaling, preventing the message to contract from reaching the diaphragm muscle.
Direct Damage to the Diaphragm Muscle
Diaphragm paralysis can originate from a defect or injury directly within the muscle tissue itself, rather than a nerve signal problem. This is a less common cause than phrenic nerve injury, but it results in the muscle being unable to contract even when signaled. This category includes primary muscle disorders, or myopathies, which cause muscle fibers to weaken or break down.
Both inherited and acquired myopathies can affect the diaphragm. Muscular dystrophies, a group of genetic diseases causing progressive weakness, may involve the diaphragm, as can certain metabolic conditions like acid maltase deficiency. In these cases, the structural integrity or energy supply of the muscle cells is compromised, preventing a strong, coordinated contraction.
Localized, mechanical damage to the muscle is another direct cause. Severe blunt trauma to the abdomen or lower chest, often from motor vehicle accidents, can cause a diaphragm rupture, which is a tear in the muscle itself. Penetrating wounds, such as from a knife or bullet, can also directly lacerate the muscle tissue, resulting in a loss of contraction and movement in the affected area.