How is respiratory muscle weakness characterized in myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas A Jowkar, MBBS; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
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Respiratory muscle weakness that produces acute respiratory failure is a true neuromuscular emergency, and immediate intubation may be necessary. Weakness of the intercostal muscles and the diaphragm may result in carbon dioxide retention as a result of hypoventilation. Respiratory failure usually occurs around the time of surgery (eg, after thymectomy) or during later stages of the disease. However, it can be a presenting feature in about 14-18% of patients with MG. [33]  Weak pharyngeal muscles may collapse the upper airway. Careful monitoring of respiratory status is necessary in the acute phase of MG. Negative inspiratory force, vital capacity, and tidal volume must be monitored carefully. Relying on pulse oximetry to monitor respiratory status can be dangerous. During the initial phase of neuromuscular hypoventilation, carbon dioxide is retained but arterial blood oxygenation is maintained. This can lull the physician into a false sense of security regarding a patient’s respiratory status.

Cognition, coordination, sensation, and muscle stretch reflexes are normal in the myasthenic patient.

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