What every physician needs to know

Diaphragm paralysis may be unilateral or bilateral and may be seen in a variety of settings. Cardiac surgery (thought to be secondary to phrenic nerve injury due to exposure to cold cardioplegic solution or nerve stretch), chest trauma, mediastinal tumors, pleural space infection, or forceful neck manipulation may be causes.

Neurologic causes may be spinal cord transection, multiple sclerosis, amyotrophic lateral sclerosis (ALS), cervical spondylosis, poliomyelitis, Guillain-Barre syndrome, phrenic nerve injury from tumor, following cardiac surgery, blunt trauma, following viral infection or radiation therapy, idiopathic phrenic neuropathy, and idiopathic brachial plexopathy (Parsonage-Turner syndrome).

Myopathic causes may be limb-girdle dystrophy, hyperthyroidism or hypothyroidism, or idiopathic.

Other causes may be malnutrition, acid maltase deficiency, amyloidosis, or connective tissue diseases, such as systemic lupus erythematosus, dermatomyositis, and mixed connective tissue disease. The cause may also be idiopathic, which is the case most of the time.


Not applicable.

Are you sure the patient has diaphragm paralysis? What would you expect to find?

A number of clinical findings are associated with diaphragm paralysis, particularly when it is bilateral. (Unilateral diaphragm paralysis is typically well tolerated in the absence of underlying lung disease or other neuromuscular dysfunction). Clinical findings include dyspnea, which is most pronounced when the patient is supine because of repositioning of abdominal contents. The presence of a paradoxical breathing pattern in which the anterior abdominal wall moves inwardly during inspiration and outwardly with forced expiration, is often found, as is hypoxemia which is commonly seen in bilateral diaphragm paralysis as a consequence of basal atelectasis.

Findings may also include worsening of hypercapnia and hypoxemia with sleep, frank respiratory failure, pulmonary hypertension, cor pulmonale, polycythemia, and abnormal chest radiographic findings, including atelectasis, pulmonary fibrosis, subpulmonic fluid collections, and pleural adhesions.

Beware: there are other diseases that mimic diaphragm paralysis:

Diaphragm paralysis may mimic many cardiopulmonary conditions that result in dyspnea, especially congestive heart failure given the presence of orthopnea.

How and/or why did the patient develop diaphragm paralysis?

The causes of diaphragm paralysis are outlined above.

Which individuals are at greatest risk of developing diaphragm paralysis?

The causes of diaphragm paralysis are outlined above.


No laboratory studies are required for the diagnosis of diaphragm paralysis though rheumatologic serologies could be considered if there is suspicion of connective tissue disease as the etiology for the diaphragm paralysis.

What imaging studies will be helpful in making or excluding the diagnosis of diaphragm paralysis?

A chest X-ray may show unilateral or bilateral hemidiaphragm elevation, low lung volumes, and associated atelectasis.

In the setting of unilateral diaphragm paralysis, fluoroscopic examination of the diaphragm during a sniff maneuver (a so-called sniff test) reveals paradoxical cephalad movement of the affected hemidiaphragm; the test is 90% sensitive for unilateral diaphragm paralysis. The sniff test may be misleading in the setting of bilateral diaphragm paralysis, as over time patients learn to exhale actively, resulting in normal upward movement of the diaphragm during expiration, followed by passive descent of the diaphragm during inspiration.

Diaphragmatic ultrasound may be used to assess muscle thickness, movement, and transdiaphragmatic pressure generation in evaluating diaphragm weakness.

Chest CT can be considered to look for specific etiologies of unilateral diaphragm paralysis such as malignancy in select cases.


With bilateral diaphragm paralysis pulmonary function testing, including measurement of the vital capacity (VC) in supine and erect positions, may be helpful. Normally, VC falls by 10% in moving from the erect to supine position. With bilateral diaphragm paralysis, VC falls by more than 50% with the change in position. Maximal inspiratory pressure is typically less than -60 cmH2O with bilateral diaphragm paralysis.

What diagnostic procedures will be helpful in making or excluding the diagnosis of diaphragm paralysis?

EMG and nerve conduction studies (including phrenic nerve conduction studies) may be useful in sorting out neuropathic versus myopathic causes of diaphragm paralysis.


Pathologic, cytologic, and genetic studies are not useful in establishing the diagnosis.

If you decide the patient has diaphragm paralysis, how should the patient be managed?

Treatment for unilateral paralysis is typically not necessary; however, surgical plication of the affected hemidiaphragm may be considered in patients with significant symptoms or for those with underlying pulmonary disease.

In the setting of bilateral paralysis, ventilatory support, including noninvasive positive pressure ventilation, may be helpful. In many cases of total diaphragm paralysis, tracheostomy with intermittent or continuous mechanical ventilation may be required.

Diaphragmatic pacing may be used in patients with high cervical spine injuries whose phrenic nerves are intact.

Preliminary data suggest that for patients not suitable for pacing due to loss of phrenic nerve integrity, surgical nerve transfer and diagphragmatic pacing can ameliorate voluntary diaphragmatic activity and regain capacity for spontaneous respiration.

Valacyclovir for 7 days was found to be helpful in a subset of patients with bilateral diaphragmatic paralysis of acute onset (suggesting a viral etiology).

What is the prognosis for patients managed in the recommended ways?

The prognosis in diaphragm paralysis depends on the underlying cause. With phrenic nerve injury following cardiac surgery, 80% recover in six months, and 90% recover in one year. In the setting of diaphragm paralysis following spinal cord injury, the paralysis may be permanent. The prognosis for recovery with unilateral diaphragm paralysis is excellent.

What other considerations exist for patients with diaphragm paralysis?

The clinical considerations in diaphragm paralysis are discussed elsewhere.