In cases of phrenic nerve palsy, diaphragmatic paralysis ensues, which is manifested by the elevation of the diaphragm muscle on the affected side (Fig. 3.36). The most important cause of the phrenic nerve palsy that should never be overlooked is malignant infiltration of the nerve by lung cancer. Other causes include postviral neuropathy (in particular, related to varicella zoster virus), trauma, iatrogenic injury during thoracic surgery, and degenerative changes in the cervical spine with compression of the C3–C5 nerve roots.