RESUMO
There is an unclear association between the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and amyotrophic lateral sclerosis (ALS), with few reports in the literature. We report the case of an 80-year-old man admitted to our emergency room with asthenia, dysphonia, dysphagia, weight loss, and euvolemic hyponatremia, indicating a SIADH. Posteriorly, the patient also developed respiratory failure, which, in association with the previous clinical presentation, led to the diagnosis of ALS. During her permanence at the hospital, the hyponatremia improved with noninvasive positive-pressure ventilation, and the association between these two identities was made. This case also shows that patients with ALS commonly suffer from chronic respiratory failure and still have a reserved prognosis.