Normal Parathyroid Hormone Activity in Hypercalcemia Associated with Thrombotic Thrombocytopenic Purpura

To the Editor: The letter by Carmosino and Feffer in the December 2 issue¹ described two patients who had hypercalcemia after receiving plasma infusions for thrombotic thrombocytopenic purpura (TTP). The authors attributed the hypercalcemia to a rise in total serum protein and a compensatory rise in parathyroid hormone activity to maintain a normal level of free calcium. We wish to report a similar case of TTP in which there was no increase in parathyroid hormone activity. A 55-year-old man was hospitalized with fever, thrombocytopenia, microangiopathic hemolytic anemia, fluctuating neurologic disturbances, and impaired renal function. He responded promptly to treatment.