Description

Often an incidental finding with chest radiograph

• It may not cause resting pulmonary symptoms unless there is underlying comorbidity such as COPD, cardiac disease, muscular weakness, obesity; but with exertion, symptoms may occur.
• Infection in the affected lung may be slow to clear.

Epidemiology

Incidence
Uncommon

Prevalence
Some literature indicate increased rate of right-sided paralysis.

• Men > women

Etiology and Pathophysiology

Interruption in the phrenic nerve conduction to the diaphragm leaflets

• On radiographic studies, the paralyzed hemidiaphragm will be elevated and accentuated dome on both PA and lateral films.
• Paralysis may be complete or incomplete.
• Paralysis may be either flaccid or spastic.
• Flaccid weakness may become spastic with improvement of underlying conditions.
• Paradoxical movement of diaphragm with respiration may cause hypoxia because excess CO₂ (hypercapnia) will move to the unaffected lung during inspiration.

Risk Factors

Neck injury, cardiothoracic surgery, blunt force trauma to chest, chemotherapy

• Metabolic or inflammatory disorders creating pressure on the phrenic nerve
• Metabolic disturbances: hypokalemia; hypomagnesemia; hypocalcemia; hypophosphatemia; low folate and vitamins B₆ and B₁₂, low thyroid studies
• Substernal thyroid, hypothyroidism, mediastinal diseases
• Aortic aneurysm
• Neoplasm
• Pneumonia, viruses such as herpes zoster
• Spinal cord disorders (syringomyelia, poliomyelitis, motor neuron disease) (1)
• Trauma or surgery disrupting neural pathway (transection, stretching, crushing, or hypothermic injury, interscalene nerve blocks)
• Blunt and penetrating trauma from motor vehicle accidents, gunshot wounds, stab wounds
• Open heart surgery, pulmonary vein ablation, atrial fibrillation cryosurgery
• Cervical spine manipulations, spinal cord injuries particularly to C3–C5 spine (1)
• Radiation therapy to brain, cervical, or mediastinal areas
• Tumor compression/mediastinal masses compression due to bronchogenic or mediastinal tumors
• Lung cancer (Most common is metastatic lung cancer ~30%.)
• Thyroid goiter
• Myopathies or neuropathies: There may be a 3- to 4-decade delay until diaphragmatic weakness develops.
• Demyelinating diseases: Guillain-Barré syndrome, multiple sclerosis, ALS, myasthenia gravis
• Neuritis from muscular dystrophy, Charcot-Marie-Tooth, diabetes, alcoholism
• Postinfective neuritis such as diphtheria, tetanus, typhoid, measles, botulism type A, zoster, and Lyme disease
• Mechanical ventilation diffuse atrophy can occur even after brief periods of mechanical ventilation (2).
• Drug cause: aminoglycosides, etoposide, vincristine, cyclophosphamide, doxorubicin, rituximab (3)

Commonly Associated Conditions

In many cases, the cause is never identified.