Tetany caused by functional hypoparathyroidism in Gitelman Syndrome: a case report

Gitelman syndrome is an autosomal recessive salt-wasting tubulopathy affecting the distal convoluted tubule, characterised by hypokalaemia, metabolic alkalosis, hypomagnesaemia, hypocalciuria, and secondary hyperreninemic hyperaldosteronism, mimicking the effects of chronic thiazide diuretic use. Although hypocalcaemia is uncommon, it can occur due to hypomagnesaemiainduced suppression of parathyroid hormone (PTH) secretion, leading to functional hypoparathyroidism. Symptomatic hypocalcaemia and tetany are extremely rare presentations of Gitelman syndrome.
We report a 30-year-old man who presented with transient loss of consciousness and muscle cramps. He had experienced similar episodes over the preceding year, accompanied by perioral numbness and salt cravings. He had previously been diagnosed with primary hypoparathyroidism based on persistently low serum parathyroid hormone (PTH) levels despite calcium supplementation. Examination revealed carpopedal spasms and a positive Chvostek sign.
Laboratory investigations revealed hypokalaemia, metabolic alkalosis, hypomagnesaemia,  hypocalciuria, and elevated renin and aldosterone levels, consistent with Gitelman syndrome and hypocalcaemia. Treatment with intravenous calcium, magnesium, and potassium resulted in symptom resolution. Due to persistent hypokalaemia, spironolactone was added. Genetic testing confirmed mutations in SLC12A3 consistent with Gitelman syndrome.
This case highlights the importance of evaluating serum magnesium in patients with unexplained or treatment-refractory hypocalcaemia. Magnesium deficiency can mimic hypoparathyroidism by suppressing PTH secretion and impairing the end-organ responsiveness to PTH. The combination of hypokalaemia, hypomagnesaemia, and hypocalciuria is characteristic of Gitelman syndrome and should prompt further evaluation, including genetic.