Unilateral diaphragmatic paralysis is usually asymptomatic and results from interruption in the transmission of nerve impulses in the ipsilateral phrenic nerve. Most commonly, this occurs secondary to nerve invasion by an adjacent pulmonary neoplasm. The second most common "cause" is idiopathic, usually affecting the right hemidiaphragm in a male patient. The seven broad categories summarizing the etiologies of unilateral diaphragmatic paralysis are as follows:

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NEOPLASMS: usually of pulmonary origin.

PHRENIC NERVE INJURY: consider surgical sectioning or stretching, cooling (during CABG), cervical chiropractic manipulation, cervical venipuncture, and birth injury.

NEURITIS: brachial neuritis (the so-called Parsonage-Turner syndrome), Herpes zoster virus infection, and vasculitis (mononeuritis multiplex).

CNS or SPINAL CORD ABNORMALITIES: neuralgic amyotrophy, stroke, multiple sclerosis, and prior rhizotomy.

NEURAL COMPRESSION: cervical spondylosis, mediastinal lymphadenopathy, and substernal goiter.

MISCELLANEOUS CAUSES: diabetes mellitus, carbon monoxide poisoning, and upper abdominal surgery.

LIVER TRANSPLANTATION
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This condition is most reliably diagnosed via a fluoroscopic "sniff test:" under real-time chest fluoroscopy, the patient is asked to perform several sniffing maneuvers. In the normal patient, there is inferior diaphragmatic exrusion/flattening/depression during a sniff. An abnormal ("positive") sniff test is one in which there is paradoxical (i.e., upward) motion of the affected hemidiaphragm during the sniff. A positive sniff test is strong evidence for diaphragmatic paralysis, although false positive rates of up to 5% have been reported. In addition, a false negative test may occur if the patient has elevated his or her hemidiaphragm during expiration by contracting the abdominal musculature.