Usefulness of phrenic nerve conduction study in early diagnosis of isolated respiratory onset amyotrophic lateral sclerosis

Isolated respiratory onset amyotrophic lateral sclerosis (ALS) is a rare clinical manifestation and the diagnosis can be challenging. A 72-year-old man presented with dyspnea and hypercapnia that had started 11 months earlier. A phrenic nerve study was conducted and he was diagnosed promptly with ALS with no significant time delay. The phrenic nerve study is a noninvasive and useful tool in the diagnosis of respiratory onset ALS that can be applied easily in an emergency department.