Approach Considerations
Diaphragm dysfunction can be difficult to diagnose, particularly when paralysis is bilateral. Workup may be triggered by unexplained dyspnea or by discovery of unilateral hemidiaphragmatic elevation on imaging. Diagnostic evaluation may include chest radiography, supine and upright pulmonary function testing, video fluoroscopy, phrenic nerve conduction studies (NCS), needle electromyography (EMG) of the diaphragm, and transdiaphragmatic pressure measurements. Each modality has its strengths and weaknesses, and all produce false-positive and false-negative findings. [6]
Laboratory studies are limited to evaluation of underlying neuropathic causes of diaphragmatic dysfunction and include viral titers and heavy metal levels. Arterial blood gas determinations may show hypoxemia with underlying ventilation-perfusion (V/Q) mismatch and progressive hypercapnia as respiratory failure develops.
Imaging Studies
Chest radiography
Unilateral diaphragm paralysis appears as an abnormally elevated hemidiaphragm on a chest radiograph, which can be defined as a right hemidiaphragm sitting more than 2 cm higher than its left counterpart or a left hemidiaphragm sitting at or higher than the right hemidiaphragm. However, it should not be taken as a decisive indication of diaphragmatic paralysis. Although chest radiography has high sensitivity (90%), there can be false-positive findings (positive predictive value of 33%), and there is relatively poor specificity (44%) for the diagnosis of diaphragm dysfunction. [5, 40]
Congenital defect or traumatic rupture is demonstrated roentgenographically with abdominal contents in the thorax on the affected side. A nasogastric tube that radiographically appears to be in the thorax may be misinterpreted as a massive hemothorax. Thus, it is always important to palpate the lung parenchyma and/or abdominal viscus within the thorax before inserting a chest tube into a patient with trauma. [41]
Chest radiographs may exhibit a cervical or thoracic mass that encompasses the phrenic nerve. Small lung volume and atelectasis are also common features. Often, a chest plain film may be interpreted as “poor inspiratory effort.”
Note the image below.
Diaphragm Disorders (Diaphragmatic dysfunction). Radiograph of a man who fell 45 ft from scaffolding, through plate glass windows, and onto the ground. Intraoperatively, he had a completely avulsed diaphragm on the left side. The patient subsequently recovered after a 45-day hospital course of treatment.
Fluoroscopy
Fluoroscopy is well validated for evaluation of unilateral diaphragmatic dysfunction. Fluoroscopy is generally performed with two to three resting tidal respirations, two to three deep respirations, and two to three hard, deep, and fast inhalations through the nose (sniff maneuvers) in both the anteroposterio and lateral views.
Fluoroscopy is considered positive if a 2-cm or greater excursion is present and the whole leaf of the hemidiaphragm is involved during the sniff maneuver. It should be noted, however, that up to 6% of the healthy population has paradoxical movement of a hemidiaphragm on a deep inspiration or during a sniff maneuver. [40]
Although fluoroscopy is positive in 90% of cases of unilateral diaphragmatic paralysis, it should not be used to diagnose bilateral diaphragm weakness. In bilateral paralysis, the sniff test result may be misleading because the cephalad movement of the ribs and accessory muscle contraction gives the false appearance of caudal displacement of the diaphragm. [41, 42]
Ultrasonography
Ultrasound evaluation of the diaphragm is noninvasive and readily available at the bedside. [43, 44] The main variables that can be assessed using this technique include the static measurement of diaphragm thickness and the more dynamic evaluation of inspiratory diaphragm thickening fraction and excursion. [45, 43, 44] In patients with serial ultrasound measurements after diaphragm paralysis, an increase in thickness of the diaphragm during inspiration, which probably correlates with reinnervation, has been associated with improvement in inspiratory function and increases in vital capacity over time. [6]
In a prospective study, 66 patients with dyspnea were evaluated with B-mode ultrasonography for possible diaphragm dysfunction due to neuromuscular respiratory failure. Results were compared to the diagnosis of diaphragm dysfunction using other diagnostic tests, including chest radiography, fluoroscopy, phrenic nerve conduction studies, diaphragm electromyography, and/or pulmonary function tests. Compared to 82 abnormal hemidiaphragms, 76 had abnormal sonographic findings (size < 2mm or decreased thickening with inspiration); compared to 49 normal hemidiaphragms, there were no false-positive ultrasound findings. Diaphragmatic ultrasound was 93% sensitive and 100% specific for the diagnosis of neuromuscular diaphragmatic dysfunction. [46]
CT scanning and MRI
Computed tomography (CT) scanning is usually not very helpful in bilateral paralysis. Dynamic magnetic resonance imaging (MRI), however, has evolved with new techniques for quantitative evaluation of excursion, synchronicity, and velocity of diaphragm motion. [6]
MRI of the neck may be useful to determine if the presence of pathologic conditions involving the spinal column and nerve roots are causing diaphragmatic paralysis.
Other Tests
Pulmonary function tests
Pulmonary function tests, including maximum inspiratory pressures, transdiaphragmatic pressure measurement, and vital capacity (VC), in both the upright and supine positions help the clinician determine whether diaphragmatic dysfunction is present and/or the degree of respiratory compromise experienced by the patient in different positions.
In healthy individuals, a 10% decrease in VC in the supine position when compared to the upright postion is typically present. In patients with unilateral diaphragmatic paralysis, VC is typically decreased by 15%-20% in the supine position. In patients with bilateral diaphragmatic paralysis, VC decreases 30%-50% in the supine position. A decrease of less than 10% in the supine position when compared to upright effectively excludes clinically significant diaphragmatic weakness. [47, 48]
Maximal inspiratory pressure (MIP) is also a useful test, although like VC, it is more useful in the assessment of bilateral diaphragmatic weakness. The benefits of MIP are that it is an easy, noninvasive test with well-established normal ranges. Limitations of assessing MIP include the fact that it is effort dependent, less reproducible than lung volumes, and of minimal benefit in the assessment of unilateral diaphragmatic weakness. Normal values of MIP are generally considered above 80 cm H2O in men, and more than 70 cm H2O in women. However, it is recognized that the normal range is wide and varies with age, sex, and body habitus. [37] For this reason, some pulmonary function testing laboratories will use a calculated lower limit of normal that calculates a more narrow range based on specific patient demographics. [49] Bilateral diaphragmatic paralysis decreases MIP by approximately 60%, and unilateral diaphragmatic weakness decreases MIP by approximately 30%. Normal MIPs can generally exclude clinically significant diaphragmatic weakness. [50]
Transdiaphragmatic pressure measurements
Measurement of transdiaphragmatic pressure (Pdi) is the considered gold standard for the diagnosis of diaphragmatic dysfunction and paralysis. It is measured by placing balloon catheters in the lower esophagus and stomach, and then calculating the difference in pressures. Measurements can be made during tidal breathing, during maximum inspiratory effort (Pdi-max), and during the sniff maneuver (Pdi-sniff). Pdi may also be augmented by transcutaneous electrical or magnetic stimulation of the phrenic nerves (twitch Pdi) to eliminate variability due to patient effort.
Pdi-sniff has been shown to have a narrower normal range and less susceptibility to variations. Normal values of Pdi-sniff are approximately more than 90 cm H2O in men and over 80 cm H2O in women, with a standard deviation of 20 cm H2O, in which a Pdi-sniff above 40 cm H2O or twitch Pdi above 15 cm H2O virtually excludes clinically significant diaphragmatic weakness. [5, 51, 49] Limitations of Pdi measurements include invasiveness, patient discomfort, and requirement of specialized equipment and expertise in their use and interpretation.
Nerve conduction and electromyography
Phrenic nerve conduction studies are used to assess the latency of conducting nervous impulses along the course of the nerve. This helps localize lesions to one side or the other as well as helps the clinician to decipher whether the condition is a bilateral phenomenon. This test is not generally available and may require referral to a center that is able to provide this service.
An electromyogram (EMG) is useful to show neuropathic or myopathic patterns, and the test can be complemented by phrenic nerve stimulation at the neck. [52]
Diaphragm EMG can detect evidence of denervation and differentiate between neuropathic and myopathic causes of paralysis with high sensitivity and specificity, and it can be performed in patients on full ventilator support. However, it is uncomfortable, can be technically challenging to perform and interpret, and carries the risk of pneumothorax. [6]
Sleep studies
Sleep-disordered breathing (SDB) is common in patients with diaphragmatic dysfunction. Results of lung function tests and daytime symptoms have been reported to be poor predictors of the presence of SDB in this population, and polysomnography should be considered early in the evaluation of diaphragm dysfunction. [53]
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Diaphragm Disorders (Diaphragmatic dysfunction). Radiograph of a man who fell 45 ft from scaffolding, through plate glass windows, and onto the ground. Intraoperatively, he had a completely avulsed diaphragm on the left side. The patient subsequently recovered after a 45-day hospital course of treatment.
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Diaphragm Disorders (Diaphragmatic dysfunction). Congenital diaphragmatic hernia is shown in this coronal obstetric ultrasound (the patient's head is to the right of the image; the thorax is center, and the abdomen is left). The stomach (st) and heart (hrt) are both within the thorax. Courtesy of Wikipedia (https://en.wikipedia.org/wiki/File:Cdh0002.jpg), author Dr Laughlin Dawes.
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Diaphragm Disorders (Diaphragmatic dysfunction). Sagittal computed tomography scan of the chest with intravenous contrast demonstrates a Morgagni hernia (red arrow) containing abdominal fat. Courtesy of Wikipedia (https://en.wikipedia.org/wiki/File:Morgagni_Hernia.PNG), author Jason Robert Young, MD.
