A 49-year-old female is admitted to the hospital with communityacquired pneumonia. On presentation to the emergency department she is complaining of shortness of breath:
CXR shows an RML lobar infiltrate. She is admitted to the general medical floor but that night complains of increased dyspnea that is worse when lying supine. She is noted to have a weak cough and difficulty clearing secretions. She is afebrile, with a pulse of 110 and BP 110/75. O2 sat remains >95% on 2 to 4 L/min NC. Exam is notable for a regular cardiac rhythm, with no murmurs, rubs, or gallops. There are bronchial breath sounds noted over the right mid-lung zone. Peripheral pulses are intact, strength is normal in the b/l upper and lower extremities and there are normal deep tendon reflexes. CXR is unchanged from admission.
Which will be most helpful in determining subsequent therapy and need for intubation?
A. Lumbar puncture and EMGCorrect Answer: B
This patient is presenting with signs and symptoms consistent with myasthenic crisis. Myasthenic crisis can be the first presentation of myasthenia gravis, an autoimmune disorder caused by development of autoantibodies which attack the neuromuscular junction. Common precipitants of crisis in patients with myasthenia include infection, with bacterial pneumonia being most common, and drugs including fluoroquinolones. Clinical features include bulbar weakness and dysphagia, dyspnea, respiratory muscle weakness (often manifested as worsening respiratory function when supine—a position in which the abdominal contents impede the motion of the diaphragm more so than in the upright position), and decreased vital capacity. Elective intubation should be considered when vital capacity declines below 15 to 20 mL/kg. Additional therapies for myasthenic crisis include plasma exchange and IVIG. Myasthenia can be associated with generalized weakness, but a proportion of patients will present with primarily respiratory weakness. Lumbar puncture and EMG can be helpful in the diagnosis of GuillainBarre syndrome but weakness in the Guillain-Barre syndrome typically starts in the legs and is associated with a lack of deep tendon reflexes. Heart failure and subsequent pulmonary edema can lead to worsening dyspnea when lying flat. BNP and TTE can be helpful in making that diagnosis, but the normal cardiac exam and unchanged CXR make that diagnosis less likely here. Heart failure would also not explain the dysphagia. Chest CT could be helpful in establishing a diagnosis of aspiration, which occurs in the setting of bulbar weakness, but in this case the CXR is unchanged and there is minimal change in the degree of hypoxemia.
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