A Case of Gitelman Syndrome that Was Difficult to Distinguish from Hypokalemic Periodic Paralysis Caused by Graves' Disease

A 21-year-old man presented with hyperthyroidism and hypokalemia and was treated for thyrotoxic hypokalemic periodic paralysis caused by Graves' disease. Thyroid function soon normalized but hypokalemia persisted. Laboratory data revealed hyperreninemic hyperaldosteronism and metabolic alkalosis consistent with Gitelman Syndrome. The patient was found to have a previously unreported compound heterozygous mutation of T180K and L858H in the SLC12A3 gene, and Gitelman Syndrome was diagnosed. He was started on eplerenone to control serum potassium level. Alternative diagnoses should be considered when electrolyte imbalances persist after disease resolution.