Case Presentation: A 65–year–old woman with squamous cell lung cancer was brought to the emergency department for altered mental status and dizziness. Her heart rate was 119 bpm and her blood pressure was 112/78 mmHg. Her ionized calcium was 1.64 mmol/L. Her PTHrP was elevated at 4.8 pmol/L. On day 2 of admission, after zoledronate, calcitonin and 3 liters of normal saline, her ionized calcium improved to 1.36 mmol/L. She remained tachycardic at 107 bpm, but her blood pressure dropped to 93/51 mmHg. The patient was started on midodrine with improvement of blood pressure to 126/62 mmHg, and heart rate to 93 bpm. She clinically improved without need for further IV fluids.
Discussion: This case highlights the hemodynamic effects of hypercalcemia and PTHrP. Initially, she had elevated heart rate and blood pressuring owing to the chronotropic and vasoconstrictive properties of hypercalcemia1. However, as this was treated, she remained tachycardic and became hypotensive due to the chronotropic and vasodilatory effects of PTHrP2,3. The mechanism of PTHrP-mediated tachycardia is influx through funny channels in the SA node, while tachycardia in hypercalcemia is by influx through calcium channels1,2. We considered ivabradine as this blocks the funny channels, however, this would not treat vasodilation. We elected to use midodrine, which would cause peripheral vasoconstriction with reflex bradycardia. This case demonstrates the complex interplay of the hemodynamic effects of PTHrP and calcium.
Conclusions: Although the association of PTHrP with hypercalcemia is well established, its effects on the cardiovascular system are under recognized. Hospitalists should anticipate the potential for hypotension as hypercalcemia is treated, removing its vasoconstrictive effect. As tachycardia can be related to either PTHrP or hypercalcemia, it may persist after correction of the calcium. It is important to recognize this cause of hypotension and persistent tachycardia, as inappropriate treatment may cause frustration and increase length of stay. Additionally, identifying the hemodynamic effects of paraneoplastic PTHrP can help prevent unnecessary, and often costly, work up for patients in the inpatient setting.