Concurrent Gitelman Syndrome and Hyperthyroidism: Diagnostic Challenges in a 51-Year-Old Patient.

BACKGROUND Gitelman syndrome (GS) is an uncommon autosomal recessive inherited disease caused by inactivating mutations in the SLC12A3 gene located on chromosome 16q13, resulting in distal tubular dysfunction. Most cases are detected during routine examinations in adulthood, due to hypokalemia and alkalosis. GS needs to be distinguished from diseases that cause hypokalemia, such as Classic Bartter syndrome and hyperthyroidism. In individual cases, GS and hyperthyroidism occur simultaneously, which is prone to misdiagnosis. CASE REPORT A 51-year-old woman with intermittent palpitations and lower limb fatigue for 4 years received a diagnosis of hypokalemia at a local hospital. Treatment with potassium supplementation did not improve the patient's palpitations and fatigue. After coming to our hospital for examination, it was found that the patient had hyperthyroidism. After receiving treatment of hyperthyroidism remission and sufficient potassium replacement, the patient's serum potassium level remained low. Meanwhile, the patient had hypomagnesemia and metabolic alkalosis. Subsequently, according to our suggestion, the patient continued to take oral supplements of potassium and magnesium, while also started on spironolactone. We convinced the patient to undergo genetic testing and discovered compound heterozygous mutations in the SLC12A3 gene, which presented a definitive diagnosis of GS. In the following 3 months, the patient's serum potassium level was within the normal range, and the dose of methimazole was reduced. CONCLUSIONS As a rare disease, GS may have only mild or occasional manifestations, making it prone to misdiagnosis. GS remains therapeutically challenging, and future progress in treatment will depend on further research of the disease.