Phrenic nerve conduction in amyotrophic lateral sclerosis.

Respiratory failure accounts for the majority of deaths in amyotrophic lateral sclerosis (ALS). The main cause of respiratory failure is probably diaphragmatic weakness. In order to test the correlation between respiratory impairment and diaphragmatic function we studied the phrenic nerve conduction in 31 ALS patients. Our results showed that patients with respiratory symptoms, and decreased forced vital capacity with arterial PaO2/PaCO2 abnormalities, had more commonly increased phrenic nerve latencies or absent response due to severe diaphragm denervation than ALS patients without respiratory complaints. Diaphragmatic paresis commonly occurs during the course of ALS, and its presence and severity can be assessed by phrenic nerve studies. It is important to recognize the development of impairment in diaphragmatic function in order to prevent life-threatening complications.