Hyperkalemia in a patient with myasthenia gravis: case presentation

Myasthenia gravis (MG) is the most common disorder of neuromuscular transmission, and it is typified by fluctuating degrees and variable combinations of weakness in the ocular, bulbar, limb, and respiratory muscles. Under rare circumstances, MG can be accompanied by Addison's disease.

Here, we reported the case of a 57-year-old Chinese woman with MG. She experienced progressive muscle weakness for 1 week. MG with acute exacerbation was initially suspected. However, further biochemistry tests found mild hyperkalemia (5.6 mEq/L) and a lower renal potassium excretion rate. Consequently, low aldosterone action was highly suspected. Further findings included a suppressed cortisol level, a higher adrenocorticotropic hormone concentration, and 21-hydroxylase antibody positivity, supporting a diagnosis of primary adrenal insufficiency due to autoimmune adrenalitis.

We successfully demonstrated that adrenal insufficiency could be diagnosed, due to the presence of hyperkalemia. This case suggested a need for clinicians to consider the possible coincidence of adrenal insufficiency in a patient with MG and hyperkalemia. Early hormone supplementation should be begun.