What are the clinical manifestations of hypercalcemia? Why does polyuria occur?
Clinical manifestations vary with acuity and severity of hypercalcemia. In the more acute settings, these include fatigue, weakness, lethargy, confusion, anorexia, nausea, abdominal pain, constipation, polyuria, and polydipsia. Cardiac abnormalities like electrocardiographic changes (short QT, ST segment elevation), arrhythmias (bradyarrhythmias or heart block), and potentiation of digitalis toxicity have been reported.
Polyuria is a manifestation of nephrogenic diabetes insipidus that occurs in hypercalcemia by the following proposed mechanisms:
• Inhibition of salt reabsorption in the medullary thick ascending limb with resultant “washing out” of the medullary interstitium and reduction of the countercurrent gradient.
• Inhibitory effect of the CaSR on vasopressin-stimulated water reabsorption in the inner medullary collecting duct.