Statin-Associated Myasthenic Weakness
Nath Pasutharnchat MD*, Kammant Phanthumchinda MD, MSc*
Affiliation : * Division of Neurology, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Background : Statin-associated myasthenic weakness is uncommonly recognized. Since 2002, there have been 14 cases
described in literatures. However, the underlying mechanism is still unknown.
Case Report : In 2007, a 50-year-old woman with generalized, limb predominated, myasthenia gravis (MG), whose MG
status has been “minimal manifestation” for several years, developed moderately severe fluctuating bulbar weakness a few
weeks after starting simvastatin 20 mg/day. Simvastatin was discontinued and dosage of cholinesterase inhibitor was
temporarily increased. The symptoms resolved and she was back to her previous status in one month. In 2008, two weeks
after re-challenge with simvastatin 10 mg/day, bulbar weakness re-occurred. Antibody to acetylcholine receptors was
measured 4.25 nmole/L. Serum creatine phosphokinase was normal. Electrophysiologic tests showed evidences of postsynaptic
neuromuscular junction disorder without evidence of myopathy. The symptoms were again resolved after discontinuation of
statin and temporarily increased dosage of cholinesterase inhibitor. She was back to previous status in two months.
Hypercholesterolemia was then controlled with ezetimibe without any worsening in MG status.
Conclusion : Because of the wide use of statins in clinical practice, physicians should be aware of this potential adverse effect.
The incidence of statin-associated myasthenic weakness should be clearly investigated. Challenge with other brands of statin
or with reduced dosage is not beneficial in these patients. Non-pharmacological treatment and non-statin medication may be
considered.
Keywords : Statin, Myasthenia gravis, Statin-associated myasthenic weakness
