Diaphragmatic weakness and paralysis.

Diaphragmatic weakness implies a decrease in the strength of the diaphragm. Diaphragmatic paralysis is an extreme form of diaphragmatic weakness. Diaphragmatic paralysis is an uncommon clinical problem while diaphragmatic weakness, although uncommon, is probably frequently unrecognized because appropriate tests to detect its presence are not performed. Weakness of the diaphragm can result from abnormalities at any site along its neuromuscular axis, although it most frequently arises from diseases in the phrenic nerves or from myopathies affecting the diaphragm itself. Presence of diaphragmatic weakness may be suspected from the complaint of dyspnea (particularly on exertion) or orthopnea; the presence of rapid, shallow breathing or, more importantly, paradoxical inward motion of the abdomen during inspiration on physical examination; a restrictive pattern on lung function testing; an elevated hemidiaphragm on chest radiograph; paradoxical upward movement of 1 hemidiaphragm during fluoroscopic imaging; or reductions in maximal static inspiratory pressure. The diagnosis of diaphragmatic weakness is confirmed, however, by a reduction in maximal static transdiaphragmatic pressure (Pdimax). The diagnosis of diaphragmatic paralysis is confirmed by the absence of a compound diaphragm action potential on phrenic nerve stimulation. There are many causes of diaphragmatic weakness and paralysis. In this review we outline an approach we have found useful in attempting to determine a specific cause. Most frequently the cause is either a phrenic neuropathy or diaphragmatic myopathy. Often the neuropathy or myopathy affects other nerves or muscles that can be more easily investigated to determine the specific pathologic basis, and, by association, it is presumed that the diaphragmatic weakness or paralysis is secondary to the same disease process.