A 68-year-old man with myasthenia gravis is evaluated for progressive weakness while hospitalized. The patient was admitted 2 days prior due to fever, productive cough, and pleuritic chest pain. Chest x-ray demonstrated a right lower lobe consolidation for which the patient has been receiving intravenous ceftriaxone and azithromycin. He also has been receiving his outpatient dose of pyridostigmine. In the past several hours, he has experienced progressive generalized weakness and an inability to cough up sputum. Temperature is 37.6 C (99.7 F), blood pressure is 130/70 mm Hg, pulse is 110/min, and respirations are 25/min. Oxygen saturation shows 89% on 4 L/min oxygen by nasal cannula. The patient appears to be in distress, and his breathing pattern is rapid and shallow with occasional gurgling sounds. Lung auscultation demonstrates coarse crackles throughout. There is mild weakness of the extremities, but deep tendon reflexes are normal. Vital capacity is now 1 L compared to 1.5 L at the time of admission, and arterial blood gas testing shows that pH is 7.27, pCO2 is 55 mm Hg, and pO2 is 60 mm Hg. The patient is intubated, and he is moved to the intensive care unit. Which of the following is the best next step in management of this patient?
Myasthenic crisis | |
Precipitating |
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Signs/symptoms |
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Treatment |
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IVIG = intravenous immunoglobulin. | |
This patient with myasthenia gravis (MG) is most likely suffering from myasthenic crisis, which is characterized by severe respiratory muscle weakness leading to respiratory failure. This condition may be precipitated by infection (eg, pneumonia), surgery, or various medications (eg, azithromycin). Individuals often have increasing generalized and bulbar muscle weakness (eg, difficulty coughing up sputum) prior to the onset of crisis. Progression leads to worsening vital capacity; hypoxia with rapid, shallow respirations; and acute respiratory acidosis (as seen in this patient).
Patients with deteriorating respiratory status (eg, decreased vital capacity, inability to protect the airway), such as this one, should first be intubated for airway protection and have mechanical ventilation. Acetylcholinesterase inhibitors (eg, pyridostigmine) used in the daily management of MG are temporarily held to reduce excess airway secretions and the risk for aspiration (Choice B).
Therapeutic plasma exchange, which rapidly reduces the level of pathologic autoantibodies, is typically performed. This effect is temporary (a few weeks), so glucocorticoids and other immunomodulatory therapy (eg, mycophenolate mofetil, azathioprine) is also started but usually requires several weeks to reach clinical efficacy.
(Choice A) Close observation and monitoring of respiratory muscle strength (eg, vital capacity, maximal inspiratory force) are important in the management of myasthenic crisis. However, observation alone is insufficient because this patient requires treatment to reverse respiratory failure.
(Choice C) Oral antimotility agents containing atropine may be used to treat the muscarinic adverse effects (eg, diarrhea) of anticholinesterase therapy in patients with MG. However, intravenous atropine has no role in myasthenic crisis management.
(Choice E) Thymectomy is generally recommended in MG patients with thymoma because it can lead to long-term clinical improvement. However, it is not the best next option for this critically ill patient.
Educational objective:
Management of myasthenic crisis with respiratory failure consists of endotracheal intubation followed by treatment with plasmapheresis (or intravenous immunoglobulins) and corticosteroids.