Case Report: Unusual electrolyte changes in primary hyperparathyroidism-a call to suspect underlying Gitelman...

Primary hyperparathyroidism (PHPT) is commonly associated with hypercalcemia, hypophosphatemia, and hypercalciuria. Hypokalemia and hypomagnesemia are rare and indicate a complicated etiology.

We describe a 74-year-old woman who presented with metabolic encephalopathy and moderate dehydration. Biochemical examinations revealed a parathyroid crisis with severe hypercalcemia (4.18 mmol/L), hypophosphatemia, hypokalemic (2.5 mmol/L) metabolic alkalosis, severe hypomagnesemia (0.23 mmol/L), and a high level of intact parathyroid hormone (243.0 pg/mL). The electrolyte imbalances were resistant to proper hydration and electrolyte replacement. Markedly, urine analysis showed renal potassium and magnesium wasting and severe hypocalciuria (calcium-to-creatinine clearance ratio, 0.0093). The presence of this paradoxical hypocalciuria despite PHPT brought into question the possibility of an underlying renal tubulopathy or accompanying vitamin D deficiency. Vitamin D assay showed deficiency with a level of 14.2 ng/mL. Ultrasound neck and contrast-enhanced computed tomography of the neck showed a right thyroid lesion for which the patient underwent right hemithyroidectomy and parathyroidectomy. Histopathological examination revealed a parathyroid adenoma. Although the patient's hypercalcemia settled postoperatively, hypomagnesemia persisted despite vitamin D supplementation, which indicates the presence of underlying renal tubulopathy, likely Gitelman syndrome.

This case emphasizes that persistent hypokalemia, hypomagnesemia, and unexpected hypocalciuria in patients with PHPT should prompt clinicians to suspect concurrent renal tubulopathies such as Gitelman syndrome.