Undiagnosed amyotrophic lateral sclerosis and respiratory failure.

Two patients suffering from exacerbation of chronic respiratory insufficiency due to previously undiagnosed amyotrophic lateral sclerosis are reported. Both patients had a false diagnosis of asthma with a restrictive component. The diagnosis had been made after pulmonary function studies, and both patients had also received treatment for asthma. A central etiology was suspected when weaning from mechanical ventilation proved unsuccessful during respiratory failure, necessitating intensive care. A neurologic examination and a typical electroneuromyography recording confirmed the diagnosis of amyotrophic lateral sclerosis. Neuromuscular disorders must be excluded when treating patients with respiratory failure, even if they already have the diagnosis of chronic pulmonary disease.