An elderly patient with Graves’s disease presenting with hypercalcemia and Gitelman syndrome – A diagnostic challenge

A 76-year-old patient with diabetes mellitus, hypertension presented with proximal muscle weakness and diarrhea. She was diagnosed with Graves’disease. She had hypokalemia, metabolic alkalosis, hypomagnesemia, hypercalcemia, hyperkaluria and hypercalciuria. High urine potassium was thought to be due to Gitelman syndrome while high urine calcium excretion settled with normalization of serum calcium. Her serum phosphate, vitamin D level were normal, PTH was suppressed. Screening for myeloma and solid organ malignancies were negative. Plasma renin and aldosterone levels were normal. One month after treatment, she reached normocalcemia and after one year her metabolic abnormalities reversed. The presence of both hypercalcemia and Gitelman syndrome at the same time mimicked Bartter syndrome. Normalization of serum calcium and urine calcium excretion with treatment of thyrotoxicosis lead to the correct diagnosis.