Background
The diaphragm, the most important muscle of ventilation, develops negative intrathoracic pressure to initiate ventilation. Innervated by cervical motor neurons C3-C5 via the phrenic nerves, these two nerves provide both sensory and motor function to the diaphragm. [1, 2] With contraction, the cone-shaped muscle of the diaphragm decreases intrapleural pressure during inspiration and thereby facilitates movement of air into the lungs. Diaphragmatic paralysis is an uncommon, yet underdiagnosed cause of dyspnea. [3]
Pathophysiology
Diaphragmatic paralyses encompass a spectrum of diseases involving a single leaflet, known as unilateral diaphragmatic paralysis (UDP), and that involving both leaflets, known as bilateral diaphragmatic paralysis (BDP).
Although the diaphragm performs most of the work, normal ventilation also requires the simultaneous contraction of respiration accessory muscles (ie, scalene, parasternal portion of the internal and external intercostal muscles, sternocleidomastoid, trapezius). In bilateral diaphragmatic paralysis, accessory muscles assume some or all of the work of breathing by contracting more intensely. An increased effort in the struggle to breathe may fatigue the accessory muscles and lead to ventilatory failure.
Etiology
Unilateral diaphragmatic paralysis
The most common diagnosed cause is a malignant (ie, metastatic lung cancer) lesion leading to nerve compression (approximately 30% of patients).
If malignancy is not the cause, many times the etiology cannot be determined.
Other causes in the differential include blunt cervical trauma, surgical trauma (mainly thoracic), [4] herpes zoster, cervical spondylosis, and supraclavicular brachial plexus block (which can be largely avoided with the use of ultrasound.) Upper cervical radiculopathies, Hashimoto encephalopathy, and neuromyelitis optica as causes of hemidiaphragmatic paralysis have also been reported. [5, 6, 7]
Bilateral diaphragmatic paralysis
The most common causes are secondary to motor neuron disease, including amyotrophic lateral sclerosis and postpolio syndrome.
Other causes include thoracic trauma, cardiac surgery, [8] multiple sclerosis, myopathies, muscular dystrophy (acid maltase deficiency), Guillain-Barré syndrome, and Parsonage-Turner syndrome (neuropathy of brachial plexus). See Complications.
Epidemiology
Frequency
Incidence is unknown.
Sex
Like diaphragm eventration, diaphragm paralysis is more common among males. [9]
Prognosis
Unilateral diaphragmatic paralysis
Depending on the etiology of the diaphragmatic paralysis, the prognosis of unilateral disease usually is excellent unless the patient has significant underlying pulmonary disease. Patients develop compensatory mechanisms, and patients with phrenic injuries may recover fully or partially. [10] At times, patients may spontaneously recover from idiopathic disease. Patients who do not recover from unilateral diaphragmatic dysfunction generally lead relatively normal lives. In this group, dyspnea may develop with exertion, leading to increased ventilatory demands.
Bilateral diaphragmatic paralysis [11]
The prognosis depends on the nature of the underlying disease. Patient diaphragm function may recover if nerve injury is not permanent, while other patients may require long-term treatment as elaborated before. If recovery occurs, it usually takes considerable time, in excess of one year.
Mortality/morbidity
Unilateral diaphragmatic paralysis
The morbidity of the unilateral paralysis is mainly based on the underlying pulmonary functional status and the etiology of the paralysis. Because most cases of unilateral diaphragmatic paralysis are found incidentally during imaging studies, many patients have no symptoms. Diaphragmatic paralysis is more likely to affect the left hemidiaphragm. [9] The patients with unilateral diaphrmatic paralysis that do have symptoms and decreased quality of life are those who have concurrent underlying lung diseases.
Bilateral diaphragmatic paralysis
Patients with bilateral diaphragmatic paralysis are usually symptomatic and, when symptoms are severe or in the presence of underlying lung pathology, may develop ventilatory failure without medical intervention.
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Acute unilateral left diaphragmatic paralysis in a patient with moderately severe chronic obstructive pulmonary disease. The patient previously was asymptomatic but developed class III dyspnea following the new event.
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Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm moves paradoxically upward during inspiration.
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Fluoroscopy of elevated left hemidiaphragm in a patient with unilateral diaphragmatic paralysis. The diaphragm does not move during expiration. For confirmation, a sniff test is required.
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Radiograph of a patient with bilateral diaphragmatic paralysis displaying low lung volumes.
