In many instances, patients with unilateral diaphragmatic paralysis may be asymptomatic, with the paralysis being found incidentally. In other cases, patients can present with varying amounts of dyspnea depending on underlying comorbidities, specifically underlying cardiopulmonary disease. In many instances, unilateral diaphragm paralysis can present similar to a variety of cardiorespiratory diseases and may be overlooked initially.[15] 

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.[1] 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.[13]

It is important to ask about medical history when a patient presents with unilateral diaphragmatic paralysis in order to obtain a cause for paralysis. There are many potential causes, and important details could be discovered from past medical history, surgeries, infections, recent trauma, or vaccination history, or recent travel.

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.[2]

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.[1] 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.[1]

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.[1]

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.[1] 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.[11]

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.[1]

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.[1] 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.[16]

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.[17]

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.[18]

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.

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.[19][20][17]

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.[1]

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.[21] 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.[22]

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.[23]

As mentioned, unilateral diaphragmatic paralysis can present similarly in appearance to other cardiopulmonary diseases. A good history, physical exam, and imaging studies are required for definitive diagnosis.

Diaphragmatic Issues

Unilateral diaphragmatic paralysis is an issue with the phrenic nerve or musculature of the diaphragm, as mentioned previously. Other diaphragm pathologies may appear similar on radiographs and present with similar findings. Diaphragmatic hernia, for example, could appear similar on radiograph with an elevated hemidiaphragm and could cause trouble breathing. Tumors below the diaphragm is another example that could occupy space and cause an elevation of one hemisphere of the diaphragm and decrease its ability to contract properly.

Pulmonary Disease

Diseases such as asthma, chronic obstructive pulmonary disease (COPD), pleural effusion, or pneumonia can present with dyspnea, much like unilateral diaphragmatic paralysis. A good physical exam and imaging can usually differentiate these disease states. Atelectasis may cause dyspnea and could also cause an elevation of the hemidiaphragm on the affected side. A hemidiaphragm may also be elevated after a surgical lobectomy. It is important to consider the possibility of diaphragm paralysis coexisting with conditions such as pneumonia or pleural effusion. Patients have had residual paralysis after cases of pneumonia or pleural effusion.[24]

Cardiac Disease

Unilateral diaphragmatic paralysis can cause orthopnea, which can be misinterpreted as heart failure. A good physical exam would be able to differentiate the two by looking for signs such as peripheral edema or jugular venous distention.

Neuromuscular Junction Disease

Disease states such as cholinergic crisis, myasthenia gravis, or Lambert-Eaton syndrome, could lead to diaphragm muscle weakness and dyspnea, similar in presentation to unilateral diaphragmatic paralysis. This would be a later sign, and a thorough history or response to edrophonium would likely be able to differentiate the disease states.

Surgeries to transfer a phrenic nerve are being considered. A Japanese study outlines the possibility of reconstructive surgery to regain the function of a damaged phrenic nerve. Animal models have shown promising results, and it is assumed the same technique can be used when compared to peripheral nerve reconstruction.[25] Rat studies have also shown that contralateral phrenic nerve transfer can improve pulmonary function.[26] It has been shown that diaphragmatic pacing is an option for the treatment of unilateral diaphragmatic paralysis, and long term outcomes are a possible area of future study. [23].

Another area of study is the use of daytime mouthpiece ventilation methods. It is proven that many patients have had an improvement in exercise tolerance with the use of noninvasive positive pressure ventilation. A study in 2017 was the first to show the improvement of exercise tolerance with mouthpiece ventilation devices, which could improve patient comfort and compliance with assisted ventilation.[27] Diagnosis is commonly made with a change in vital capacity between seating and supine positioning for diaphragmatic dysfunction. A study done in 2017 showed comparable sensitivity and specificity when comparing maximal expiratory and inspiratory pressures and concluded this technique could be used to assist with the diagnosis of diaphragm dysfunction.[28]

In general, the prognosis for unilateral diaphragmatic paralysis is good. In most cases, patients may remain asymptomatic, while symptomatic patients usually end up having some resolution with time even without treatment. Prognosis is worse for patients with underlying cardiopulmonary compromise, or there is an exacerbation of an underlying condition. Prognosis is also worse if the cause of the paralysis is an illness that has high morbidity or mortality. There are multiple causes for unilateral diaphragmatic paralysis, and determining the underlying etiology is important for selecting the treatment choice and improving the prognosis.

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.[1] 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.

There are many possible etiologies for postoperative dyspnea or respiratory compromise. Depending on the surgery, unilateral diaphragmatic paralysis may be on the differential, although other more common etiologies may be more realistic. One study considered acute myasthenic states, injury either to the phrenic nerve or diaphragm, or medication effects (such as persistent neuromuscular blockade) to be the essential clinical scenarios to be aware of when considering diaphragm paralysis.[29]

The diaphragm is considered the most important muscle when it comes to respiration. Unilateral diaphragmatic paralysis is a condition when one half of the diaphragm is paralyzed. Each side of the diaphragm is innervated or controlled by the ipsilateral phrenic originating from cervical nerve roots three through five. Diaphragm paralysis can occur because of any pathology that affects the diaphragm muscle itself or interferes with the phrenic nerve’s ability to properly send signals to the diaphragm muscle. There are many possible causes for diaphragm paralysis, although the most common etiology is trauma-related.

In most cases, the unilateral paralysis is asymptomatic, and if symptoms are present, it usually improves with time without treatment. Symptoms are more common if there are underlying heart or lung issues or obesity. When symptomatic, most patients experience trouble breathing, which is worse with exercise and lying flat on their back at night. There are imaging options to assist with the diagnosis of this condition, and the treatment is more specific to the underlying cause of diaphragm weakness. Treatments can range from conservative measures, watching and waiting, to surgery to correct the underlying issue.

Unilateral diaphragmatic paralysis is a disease process that is often overlooked, as most patients are asymptomatic, and the condition is incidentally found. When compounded with lung conditions, such as pneumonia or COPD exacerbations, unilateral diaphragmatic paralysis may also be present and overlooked. In most cases, when the underlying exacerbating factor is corrected, patients will return to baseline and be discharged feeling well. Diaphragm paralysis may be overlooked as the treatment for lung conditions may also assist with diaphragm paralysis, such as non-invasive positive pressure or invasive ventilation. After certain procedures or nerve blocks, diaphragm paralysis may be expected, and when diagnosed, treatment must be directed towards the underlying cause. In some cases, it is best to treat conservatively, and in others, surgery may be necessary to correct respiratory failure.

There are many potential causes of unilateral diaphragmatic paralysis. When a patient is being worked up for an underlying cause of unilateral diaphragmatic paralysis, multiple teams may need a consultation to determine proper diagnosis and treatment for a patient. An internal medicine team will often begin the workup or discover the diagnosis. Neurology may need to assist with neuromuscular disorders and to help determine the location of lesions and the underlying cause. Surgery teams can assist in treatments, or the condition may be a result of previous surgery. Pulmonary and cardiology teams may be consulted, as dyspnea and respiratory failure can ensue if the condition remains untreated, and it will often mimic cardiac disorders. If respiratory failure does occur, a critical care team should be on board for closer monitoring and ventilator management.

Once considered in a differential, X-ray was traditionally used to screen, and fluoroscopy was then used to confirm the diagnosis. This process took time and caused patient exposure to radiation. Now, with ultrasound being so radially available and advanced, radiation has been replaced by bedside ultrasound in most instances with similar diagnostic outcomes.[1] Once diagnosed, treatment options should be targeted towards the cause of diaphragm paralysis. Prognosis is good in most cases unless the underlying cause of diaphragm paralysis holds a high mortality rate.