Myasthenia gravis is characterized by impairment of neuromuscular junction transmission due to antibody-mediated attack on (mostly) acetylcholine receptors at the postsynaptic membrane. It is associated with fluctuating weakness; excessive fatigability with exercise; ocular and bulbar muscle involvement manifesting as ptosis and diplopia; dysarthria; dysphagia, and dyspnea; as well as limb weakness. Diagnosis of myasthenia gravis is made with these typical clinical features in conjunction with positive testing for anti-acetylcholine receptor or MuSK antibodies, repetitive nerve stimulation, and single-fiber EMG. Less robust but supportive testing also includes the Tensilon and ice pack test.
Patients with myasthenia gravis may present to the ER with respiratory failure constituting a myasthenic crisis. This is usually precipitated by infection, surgery, pregnancy, systemic illness, medications, or emotional stress. It is very important to determine the need for intubation and mechanical ventilation in a timely fashion especially since mortality in myasthenic crisis is about 5 %. Culprit medications known to exacerbate myasthenia gravis should be discontinued. In myasthenic crisis, acetylcholinesterase inhibitors like pyridostigmine are usually discontinued due to the increased respiratory secretions they may cause. The definitive management is immune-modulating therapy with plasmapheresis or intravenous immunoglobulin and steroids.
Cholinergic crisis is caused by overmedication and is characterized by increased salivation and secretions, diarrhea, abdominal cramps, miosis, fasciculations, and bradycardia. Cholinergic crisis must be carefully distinguished from myasthenic crisis because the respective treatments are opposite. Hence, cholinergic crisis is treated by decreasing the dose of acetylcholinesterase inhibitor medication.
KeywordsMycophenolate Mofetil Acetylcholinesterase Inhibitor Respiratory Compromise Maximum Inspiratory Pressure Myasthenic Crisis