Myasthenia Graves (MG) is an autoimmune disorder wherein antibodies attack acetylcholine nicotinic postsynaptic receptors at the myoneural junction, resulting in muscle fatigue (commonly bulbar) that worsens with use and improves with rest. MG flares are most commonly due to infection or inadequate treatment with cholinesterase inhibitors.
The Tensilon (edrophonium) challenge test can be used to help distinguish an MG crisis from a cholingergic crisis. Once the airway and ventilation are secure, escalating doses of edrophonium (i.e. 1 mg, then 3 mg, then 5 mg, up to a maximum of 10 mg total) can be administered with the goal of relieving the muscle weakness. If a true MG crisis is present, patients usually respond with dramatic improvement within 1 minute. Patients having a cholinergic crisis, on the other hand, typically respond with increased salivation, bronchopulmonary secretions, diaphoresis, and gastric motility.
Monitor closely as edrophoniumcan cause significant bradycardia, heart block, and asystole (only 0.16% risk by reports, but have atropine nearby).
Once the edrophonium wears off, patients having an MG crisis may develop increased secretions and respiratory distress as their muscle weakness returns, so manage expectantly and with caution.
References
Grob D, Brunner N, Namba T, Pagala M. Lifetime course of myasthenia gravis. Muscle Nerve. Feb 2008;37(2):141-9.
Meriggioli MN, Sanders DB. Advances in the diagnosis of neuromuscular junction disorders. Am J Phys Med Rehabil. Aug 2005;84(8):627-38.
PascuzziRM. Pearls and pitfalls in the diagnosis and management of neuromuscular junction disorders. SeminNeurol. Dec 2001;21(4):425-40.
