Respiratory failure in myasthenia gravis due to vocal cord paresis.

Paroxysmal dyspnea and stridor in a patient with myasthenia were shown to be due to weakness of vocal cord abductors that improved with anticholinesterase therapy. Despite adequate inspiratory force, breathing was severely impaired by increased inspiratory resistance. The inspiratory flow-volume loop was useful in documenting the laryngeal obstruction and monitoring the effect of therapy. Reinterpretation of previous studies suggests that upper airway obstruction may often contribute to respiratory failure in patients with myasthenia.