Unilateral Paralyzed Hemidiaphragm (UPD)



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.



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.

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