Unilateral Diaphragmatic Paralysis – Causes, Symptoms

Unilateral diaphragmatic paralysis is a condition in which either the right or left side of the diaphragm loses the ability to contract to allow proper inspiration. This can be the result of muscular issues in the diaphragm or loss of innervation from the phrenic nerve to the hemidiaphragm. This can impact daily living by causing dyspnea at rest or during exercise, sleep disturbances, or in severe cases, decrease life expectancy. There are multiple potential causes for diaphragm dysfunction, including trauma or compression of the phrenic nerve, to medications, to demyelinating disorders, disease states, or even congenital causes. This review is to provide an overview of unilateral diaphragmatic paralysis based on current literature to help with a better understanding of the topic, improve the clinical ability to recognize the condition and a review of diagnostic and treatment options.

Bilateral diaphragmatic paralysis is a rare cause of respiratory failure that is poorly recognized and underdiagnosed. There is often a delay in making the diagnosis, especially in patients who are ventilator dependent (1). Here, we report a case of acute respiratory failure secondary to bilateral diaphragm paralysis as a complication of endoscopic ultrasound (EUS)–guided celiac plexus neurolysis (rx).


The diaphragm is a dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. The diaphragm has the ability to contract and create a negative intrathoracic pressure to allow passive air movement into the lungs. This is to allow gas exchange and proper ventilation. Other accessory muscles assist with breathing, such as the scalenes, intercostals, and sternocleidomastoid muscle, but none are as important as a properly functioning diaphragm. Each hemidiaphragm is innervated by the ipsilateral phrenic nerve, composed of cervical spinal nerves three through five, which is important for proper ventilation.

Unilateral diaphragmatic paralysis is a condition in which one hemidiaphragm is paralyzed or weakened secondary to some underlying condition. This paralysis can be due to any issue from the spinal cord to the phrenic nerve or the muscle itself, and there are varying degrees of paralysis. The severity of unilateral diaphragmatic paralysis is related to the underlying cause. Some causes are expected and are secondary to a procedure being done with full recovery expected in a given time frame, and other causes can be permanent.

When weakness or paralysis of a hemidiaphragm exists, a patient may be asymptomatic or experience dyspnea, which may be more pronounced if there are other comorbidities or lung conditions. Different studies have concluded that exercise tolerance is greatly diminished with unilateral diaphragm paralysis if obesity is comorbidity. An otherwise healthy patient may be able to compensate for the hemidiaphragm paralysis with the proper functioning hemidiaphragm and the assistance of accessory muscles. Immediately after paralysis, the working hemidiaphragm may produce enough negative intrathoracic pressure to compensate for the paralyzed side. Over time the work of breathing gets easier as the paralyzed hemidiaphragm becomes less compliant, and less of a paradoxical movement is seen with inspiration, allowing for better gas exchange. Not all patients will require treatment, and some studies mention that surgery should be reserved for patients with mediastinal shift and respiratory failure.

Causes of Unilateral Diaphragmatic Paralysis

There are many possible causes for unilateral diaphragmatic paralysis, and can either be due to issues in the musculature of the diaphragm or secondary to phrenic nerve pathology. The severity of the paralysis is dependent upon the underlying cause and can be corrected in some cases with no long term deficits, or can be permanent in other instances. The causes of unilateral diaphragmatic paralysis can be divided into different etiologies, listed below.

  • Traumatic – Trauma is considered the most common cause of diaphragm weakness. Direct trauma, either blunt trauma or during a surgical procedure, has the potential to injure the phrenic nerve leading to hemidiaphragm weakness or paralysis. The highest risk is during cardiac bypass cases, where up to 20 percent of cases result in temporary diaphragm weakness due to the cooling necessary for the procedure. Cases have also been reported during mediastinal, esophageal or lung surgeries, and even with laparoscopic cholecystectomy.
  • Compression – Compression of the phrenic nerve, whether in the form of cervical spondylosis or from an adjacent tumor or malformation, can lead to a decreased ability to function properly. Up to 5 percent of lung cancer cases have shown phrenic nerve involvement.
  • Neuropathic – Disease states that often cause nerve damage or demyelination may lead to diaphragm paralysis or weakness by interfering with the conduction of the phrenic nerve. Diabetic neuropathy can cause damage to the phrenic nerve, especially if glucose is not tightly controlled. Multiple sclerosis could also diminish the function of the phrenic nerve, depending on the location of the lesions, along with other chronic demyelinating disorders. Studies have also shown that neuralgic amyotrophy may also be a commonly overlooked etiology, with 7.6 percent of these patients having phrenic nerve involvement.
  • Inflammatory – Viruses such as Herpes zoster, Zika, Poliovirus, and other viral infections have been linked to unilateral diaphragmatic paralysis. A case series of congenital Zika syndrome reported 4 infants with diaphragm weakness that eventually died secondary to respiratory failure. Other than viral infections, some bacterial infections, such as Lyme disease, are known to affect the phrenic nerve. Noninfectious inflammatory causes have been noted to cause diaphragm weakness, including sarcoidosis and amyloidosis. Case reports have pointed at neuromyelitis optics as a culprit of unilateral diaphragmatic paralysis as well.
  • Iatrogenic – Many times in the preoperative or postoperative settings, patients will receive nerve blocks to assist with pain control. Local spread of anesthetic can affect the phrenic nerve and block impulses being sent to the diaphragm and cause unilateral diaphragmatic paralysis. This phenomenon has been reported with many blocks but more commonly seen in interscalene, brachial plexus nerve blocks, and high thoracic paravertebral nerve blocks.
  • Idiopathic – There have been many cases if both unilateral and bilateral diaphragmatic paralysis and weakness for which the cause is considered unknown. Nearly 20% of the cases have been considered idiopathic.

Symptoms of

Symptoms of significant, usually bilateral diaphragm weakness or paralysis are shortness of breath when lying flat, with walking or with immersion in water up to the lower chest. Bilateral diaphragm paralysis can produce sleep-disordered breathing with reductions in blood oxygen levels.

Newborns and children with unilateral diaphragmatic paralysis may experience more severe respiratory distress than adults, due to weaker muscles and a more compliant chest wall. The newborn may have a weak cry or show signs of gastrointestinal distress, with frequent vomiting. Children with bilateral diaphragmatic paralysis require immediate medical attention and ventilator intervention because the condition can be life-threatening.

Diagnosis of Unilateral Diaphragmatic Paralysis

History and Physical

One-third of patients may experience exertional dyspnea, while others with more comorbidities are reporting dyspnea at rest. These patients experience hypoventilation, which can lead to hypercapnia, which worsens during sleep and may lead to daytime fatigue. Immediately after unilateral diaphragmatic paralysis, symptoms may be at their worst since the body has not had time to compensate. Studies using electromyography (EMG) have shown that trans-diaphragmatic pressures may drop as much as 45 percent during airway occlusion immediately after injury, but after two weeks improved to only a 25 percent drop from baseline due to compensation mechanisms.

A physical exam may reveal non-specific findings for unilateral diaphragmatic paralysis. The exam may seem benign in an otherwise healthy individual. Occasionally there may be dullness to percussion or diminished breath sounds at the lung base on the affected side. During sleep, paradoxical thoracoabdominal movement may be seen, along with the complaint of orthopnea in the supine position, which improves with lateral positioning with the healthy lung down. Sleep respiratory disorders are also commonly associated with unilateral diaphragmatic paralysis, specifically during REM sleep.


When evaluating a patient with suspected diaphragmatic paralysis, it is important to take into consideration what the underlying cause is. For example, if a patient underwent cardiac surgery, it is known that up to 20 percent of patients have residual weakness due to the cooling of the phrenic nerve that resolves with time. An extensive workup is not likely required urgently for these patients. A diagnosis can be made based on a combination of the patient’s history, physical exam findings, imaging, and other tests.

  • Chest Radiographs – As mentioned previously, many cases of unilateral diaphragmatic paralysis are asymptomatic, leading to some cases being found incidentally by chest radiographs. Chest X-ray alone can diagnose up to 90 percent of unilateral diaphragmatic palsy. The right hemidiaphragm is usually slightly elevated when compared to the left side, and therefore if it is further elevated with a more acute costophrenic angle, one could suspect right diaphragm paralysis. If the left hemidiaphragm was similar height as the right, you might suspect left hemidiaphragm paralysis.
  • Fluoroscopic Evaluation – If a patient is suspected of having unilateral diaphragmatic paralysis based on chest X-ray findings, confirmation of the diagnosis can be through fluoroscopic examination. In unilateral diaphragmatic paralysis, the paralyzed hemidiaphragm will either show no movement or have a paradoxical movement into the thoracic cavity with sniffing or deep inspiration.
  • Pulmonary Function Tests – The diaphragm is the most important muscle for inspiration, accounting for up to 80 percent of the power generated during respiration. With unilateral diaphragmatic paralysis, a 50 percent decline would be expected in the forced vital capacity. This is further decreased up to 25 percent more during supine positioning due to muscle weakness and cranially directed pressure from the abdominal cavity. Other pulmonary volumes may remain unchanged as long as the paralysis remains unilateral. Studies have shown worse results when the unilateral paralysis is on the right side as opposed to the left. Some pulmonary function test studies show that unilateral diaphragmatic paralysis in obese patients can cause a more significant decline in exercise tolerance than just having one or the other condition.
  • Electromyography (EMG) – Electromyography has somewhat of a limited role in the diagnosis of unilateral diaphragmatic paralysis. If the issue is localized to the phrenic nerve, stimulation of the nerve will not cause muscle contraction, and this can be detected. If the pathology is muscular in origin, the phrenic nerve will conduct the impulse as expected, but the diaphragm muscle will not contract.
  • Transdiaphragmatic Pressure Measurements – In unilateral diaphragmatic paralysis, transdiaphragmatic pressures would be expected to be reduced as the diaphragm cannot contract properly. With left hemidiaphragm paralysis more than right, the gastric component of transdiaphragmatic pressure measurement is decreased.
  • Thorax Ultrasound – Ultrasound of the thorax can be used to assist with the diagnosis of diaphragm paralysis. The B mode of ultrasound can show the diaphragm as a thick echogenic line. The M mode has been used to show the movement of the paralyzed diaphragm and can show no motion or a paradoxical movement with quiet breathing, voluntary sniffing, or deep breathing.
  • CT Scan – Once patients have been diagnosed with unilateral diaphragmatic paralysis, a CT scan can be beneficial to determine the cause of the paralysis along with rule out any possible compression from tumors or other thoracic etiology. Another common finding is atelectasis at the base of the lung on the affected side.
  • MRI – An MRI may be considered if the patient presents with cervical spine pain or for a closer look at soft tissue after trauma to diagnose the etiology of the diaphragm weakness accurately. A case report of a patient who underwent foraminotomies after foraminal stenosis was seen on MRI reported resolution of hemidiaphragm paralysis.
  • Sleep Study – As mentioned earlier, with unilateral diaphragmatic paralysis, the ability to ventilate may diminish and lead hypercapnia that worsens during sleep. Some studies recommend the use of sleep studies or continuous pulse oximetry to titrate continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) for these patients to improve ventilation.
  • Laboratory Tests – Lab testing is non-specific for unilateral diaphragmatic paralysis. Testing can be done to assess underlying conditions that potentially cause the diaphragm paralysis, such as thyroid tests or serology for Borrelia burgdorferi in suspected Lyme disease. Other tests such as a complete blood count may be considered as part of the initial workup to rule out anemia as a potential cause for dyspnea.

Treatment of Unilateral Diaphragmatic Paralysis

In many cases of unilateral diaphragmatic paralysis, the patient is asymptomatic, and the paralysis is found incidentally. No intervention is required in this case, as the condition is not impacting the patient’s quality of life. The prognosis in these patients is considered good as long as there are no underlying cardiopulmonary conditions. In other cases, it is satisfactory to wait and watch, for example, in the case of cooling from cardiac surgeries or after a nerve block suspected of causing weakness. The function of the phrenic nerve is expected to return to baseline function as time goes by without intervention. For symptomatic patients, or when the condition is more acute with correctable causes, other treatment options exist.

Correct the Underlying Issue

If an underlying cause for the unilateral diaphragmatic paralysis can be determined, the treatment option should be targeted towards that pathology. For example, if there is an underlying viral etiology suspected of causing the muscle weakness because of inflammation to the phrenic nerve, the best option would be antivirals specific to that virus with or without the addition of steroids. If the underlying issue is due to compression of the phrenic nerve secondary to a cervical pathology, decompression would be the best option. Studies have shown that when a surgical option is present, such as decompression or grafting, it may result in substantial improvement in respiratory function.

Ventilatory Support

Non-invasive positive pressure ventilation or invasive ventilation can be a treatment option for unilateral diaphragmatic paralysis if needed. Many times asymptomatic patients may become symptomatic if they develop a lung pathology or experience an exacerbation of underlying pathology, and assisted ventilation strategies may be used temporarily until the patient returns to baseline status. This option is not a cure, it only corrects the ventilation deficit. CPAP or BiPAP can be considered for many patients who are mildly symptomatic, or for use at night time as supine positioning worsens dyspnea with diaphragm weakness.

Surgical Plication

In symptomatic patients, a surgical plication is an option for treatment. It is recommended to wait at least 6 months, if possible, before proceeding with this surgical option as most cases of symptomatic unilateral diaphragmatic paralysis improve with time. The concept of the procedure is to suture the diaphragm into a stable position, thereby eliminating the paradoxical movement with inspiration. This procedure can now be done robotically and minimally invasive. This option has been proven in many studies to improve vital capacity, exercise tolerance, and dyspnea. Another case study done showed improvement in pulmonary function tests along with an increase of PO2 from 70 to 87 mmHg, improved transdiaphragmatic pressures, and more effective diaphragmatic recruitment.

Phrenic Nerve Pacing

Phrenic nerve pacing is an option for patients with diaphragmatic paralysis who do not suffer from denervation of the diaphragm. This pacemaker stimulates the phrenic nerve to cause the diaphragm to contract as it would physiologically. Studies are showing promising results for diaphragmatic pacing. One study of 27 patients resulted in improvement in 81 percent of patients, four of which were able to be weaned off a ventilator.


Complications of unilateral diaphragmatic paralysis are often limited as long as other comorbidities are not present. Complications such as dyspnea, exercise intolerance, or hypercapnia may arise if left untreated with respiratory failure being the most dreaded complication. Unilateral diaphragmatic paralysis may represent a complication, in itself, of a procedure that took place to a patient.

As mentioned earlier, as high as 20 percent of cardiac bypass surgery may have diaphragm weakness as a complication. Another common reason is residual weakness after a nerve block, both of which are expected to resolve with conservative management. There are various treatment options for diaphragmatic paralysis, as discussed earlier, many of which are surgical. With each operation to treat unilateral diaphragmatic paralysis, there are always associated risks, such as bleeding, infection, damage to a local structure, or need for further procedures.


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