Severe Hypomagnesemia Unmasking Suspected Type V Bartter Syndrome: A Case Report

Introduction: Hypomagnesemia is a frequently under-recognized electrolyte disturbance that can present with neuromuscular and cardiovascular manifestations. Renal magnesium wasting is a rare but important etiology, especially when associated with inherited tubulopathies such as Bartter syndrome. We present a case of severe, persistent hypomagnesemia in a patient ultimately suspected to have Type V Bartter syndrome. Case Description: A 63-year-old female with a history of hypertension, diabetes type 2, and prior history of acute kidney injury presented with progressive whole-body jerky movements and generalized weakness. Labs revealed serum magnesium of 0.7 mg/dL and elevated lactic acid (2.6 mmol/L), without infection or other obvious etiology. A similar episode with severe hypomagnesemia and hypocalcemia occurred 6 months prior. Workup revealed a 24-hour urine magnesium of 365 mg and fractional excretion of magnesium of 81.6%, indicating profound renal magnesium wasting. Urine calcium was normal (150 mg/24h), arguing against Gitelman syndrome. Given the presence of intermittent severe hypocalcemia and absence of hypocalciuria, Type V Bartter syndrome—linked to gain-of-function mutations in the calcium-sensing receptor—was considered. The patient required aggressive intravenous magnesium replacement with symptomatic improvement and resolution of jerky movements. Oral magnesium oxide was initiated along with empagliflozin, which has been shown to reduce urinary magnesium excretion. She was discharged in stable condition with outpatient nephrology and neurology follow-up, and pending genetic testing. Discussion: This case highlights the importance of considering renal magnesium wasting in patients with unexplained neuromuscular symptoms and chronic hypomagnesemia. The biochemical profile and clinical history strongly suggest Type V Bartter syndrome, a rare cause of hypomagnesemia that warrants further genetic confirmation. Persistent, severe hypomagnesemia with neuromuscular symptoms should prompt evaluation for renal magnesium wasting. In the absence of hypocalciuria, Type V Bartter syndrome should be suspected. Early diagnosis and targeted management can significantly improve clinical outcomes.