Common symptoms are those of hypokalemia and hypocalcemia, with weakness and muscle cramps. Marked neuromuscular and central nervous system hyperirritability may produce tremors, athetoid movements, jerking, nystagmus, Babinski response, confusion, and disorientation. Cardiovascular manifestations include hypertension, tachycardia, and ventricular arrhythmias.
Urinary excretion of magnesium exceeding 10–30 mg/day or a fractional excretion greater than 2% indicates renal magnesium wasting. Hypocalcemia and hypokalemia are often present. The ECG may show prolonged QT interval due to lengthening of the ST segment. PTH secretion is often suppressed (see Hypocalcemia).