A 71-year-old man arrives to the emergency room appearing cyanotic and having weak, shallow respirations. He is brought in by his home care nurse, who reports that the patient has a history of myasthenia gravis and frequent urinary tract infections. The patient was in his normal state of health until 5 days ago when he developed a urinary tract infection. He was receiving gentamicin infusions for his infections. This morning, he experienced poor grip strength and progressive difficulty breathing. The patient’s medications include pyridostigmine and aspirin, both of which he takes as prescribed. His temperature is 99.0°F (37.2°C), blood pressure is 128/78 mmHg, pulse is 92/min, and respirations are 28/min with an oxygen saturation of 86% O2 on room air. The patient has gray-blue skin, hypophonia, weak upper extremities, and normal leg strength. An arterial blood gas is drawn with results as shown below:

PO2: 55 mmHg
PCO2: 60 mmHg
pH: 7.30

The patient is intubated. Which of the following is the most appropriate next step in management?
Edrophonium
Plasmapheresis
Thymectomy
Atropine
Plasmapheresis
This patient is presenting with a history of myasthenia gravis, recent exposure to an aminoglycoside, and respiratory failure, suggesting a diagnosis of myasthenic crisis. The most appropriate initial step in management is intubation and plasmapheresis.

Myasthenic crisis is an exacerbation of myasthenia gravis caused by under-dosing myasthenia gravis treatments or precipitated by infection, surgery, and certain medications such as aminoglycosides and beta-blockers. Symptoms include bulbar muscle weakness and type 2 respiratory failure (inadequate alveolar ventilation). The most appropriate initial step in management is to maintain adequate respiratory function by intubation. Plasmapheresis or IVIG is used to remove acetylcholine receptor antibodies from circulation, and steroids are started for long-term therapy. Avoiding risk factors and pre-medication before procedures with acetylcholinesterase inhibitors is important for preventing repeat occurrences.

Rodrigues et al. review the evidence regarding the occurrence of myasthenic crisis in patients with COVID. They discuss how treatment with IVIG and plasma exchange were important in the care of these patients. They recommend also considering whether rituximab and tocilizumab may be effective in these cases.

Incorrect Answers:
Answer A: Atropine can be used in a cholinergic crisis. A cholinergic crisis is an acute exacerbation of muscle weakness due to over-medication with cholinergic anti-cholinesterases. This disease would present with diarrhea, sweating, miosis, bronchoconstriction, and bradycardia. It rarely occurs with proper dosing of pyridostigmine.

Answer B: Edrophonium can be used in the diagnosis of myasthenia gravis. It is a cholinesterase inhibitor. In a positive test, a patient will exhibit temporary resolution of muscle weakness. In this patient’s case, the diagnosis of myasthenia gravis has already been made and he also had a recent exposure to a pharmaceutical known to precipitate myasthenic crisis.

Answer C: Neostigmine is an acetylcholinesterase inhibitor used in the management of myasthenia gravis, but it is contraindicated in the initial treatment of myasthenic crisis. Acetylcholinesterase inhibitors may increase respiratory secretions, which can worsen respiratory failure.

Answer E: Thymectomy is indicated in refractory cases of myasthenia gravis (and for increased risk of thymoma). In an unstable condition such as myasthenic crisis, thymectomy should be deferred. For patients over the age of 60, thymectomy is controversial.

Bullet Summary:
Myasthenic crisis can be precipitated by infection, surgery, and medications (aminoglycosides and beta-blockers) and should be managed with intubation followed by plasmapheresis or IVIG.