Fast Five Quiz: Refresh and Test Your Knowledge of Myasthenia Gravis

Amy Kao, MD


July 06, 2021

MG is idiopathic in most patients. Genetic variations probably increase the risk for MG, but specific mutations are currently unidentified. Although the main cause behind its development remains speculative, the end result is a derangement of immune system regulation, resulting in autoimmunity.

MG is clearly an autoimmune disease in which the specific antibody has been characterized in most cases. In the vast majority of patients, immunoglobulin G specific to AChR is present.

Various drugs may induce or exacerbate symptoms of MG, including the following:

  • Antibiotics (eg, aminoglycosides, polymyxins, ciprofloxacin, erythromycin, and ampicillin)

  • Penicillamine: This can induce true myasthenia, with elevated anti-AChR antibody titers seen in 90% of cases; however, the weakness is mild, and full recovery is achieved weeks to months after discontinuing the drug.

  • Beta-adrenergic receptor blocking agents (eg, propranolol and oxprenolol)

  • Lithium

  • Magnesium

  • Procainamide

  • Verapamil

  • Quinidine

  • Chloroquine

  • Prednisone

  • Timolol (ie, a topical beta-blocking agent used for glaucoma)

  • Anticholinergics (eg, trihexyphenidyl)

  • Neuromuscular blocking agents (eg, vecuronium and curare): These should be used cautiously in myasthenic patients to avoid prolonged neuromuscular blockade

  • Nitrofurantoin: This has also been linked to the development of ocular MG in one case report; discontinuing the drug resulted in complete recovery.

  • Cancer immunotherapy (immune checkpoint inhibitors)

    • Ipilimumab-induced (anti-CTLA4) MG

    • PD-1, PD-L1 inhibitors

MG can occur at any age. Epidemiologic data show that early-onset (< 50 years) MG is more common among women, while late-onset (≥ 50 years) disease is more common among men but overall is approximately equal at 1.1:1 (female:male). Comorbidity with a second autoimmune disease occurs more frequently among women. Ocular MG shows a male preponderance. About two thirds of patients with ocular MG can progress to generalized MG within the first 2-3 years of initial presentation. In a pediatric population, MG generally occurs more frequently in girls.

Learn more about the etiology and epidemiology of MG.


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