A 17-year-old boy is brought to the emergency department following a motor vehicle accident. He is found to have an extensive cerebral hemorrhage leading to deep coma, as well as fractures of the C4 vertebra, pelvis, and right femur. Following admission to the hospital, he is intubated and central lines are placed. The patient develops acute renal failure due to rhabdomyolysis, which improves rapidly with treatment. He is extubated after regaining consciousness. He also undergoes percutaneous endoscopic gastrostomy tube placement due to persistent problems with swallowing. The patient is unable to ambulate due to quadriparesis resulting from cervical cord injury. Four weeks after his initial injury, he develops nausea and polyuria. His laboratory results are as follows: Which of the following is the most likely cause of this patient's hypercalcemia?

Question

A 17-year-old boy is brought to the emergency department following a motor vehicle accident.  He is found to have an extensive cerebral hemorrhage leading to deep coma, as well as fractures of the C4 vertebra, pelvis, and right femur.  Following admission to the hospital, he is intubated and central lines are placed.  The patient develops acute renal failure due to rhabdomyolysis, which improves rapidly with treatment.  He is extubated after regaining consciousness.  He also undergoes percutaneous endoscopic gastrostomy tube placement due to persistent problems with swallowing.  The patient is unable to ambulate due to quadriparesis resulting from cervical cord injury.  Four weeks after his initial injury, he develops nausea and polyuria.  His laboratory results are as follows:  Which of the following is the most likely cause of this patient's hypercalcemia?

Quizplus · Accepted Answer

11ec25c8_d8ca_aa3a_bc81_cb712a964de2_MD0003_00 This patient with quadriparesis has a corrected calcium level of 12.9 mg/dL: 11ec25c8_d8ca_aa3b_bc81_7111ad5beeeb_MD0003_00 with symptomatic hypercalcemia (nausea, polyuria) and suppressed parathyroid hormone (PTH) level likely due to immobilization. Hypercalcemia of immobilization is likely due to increased osteoclastic bone resorption. The risk is increased in patients with a pre-existing high rate of bone turnover (eg, younger individuals, Paget disease). The onset of hypercalcemia is usually around 4 weeks after immobilization, although patients with chronic renal insufficiency may develop hypercalcemia in as little as 3 days. The onset of hypercalcemia due to immobilization is often insidious, and the presenting symptoms can be nonspecific. Bisphosphonates inhibit osteoclastic bone resorption and are effective in treating hypercalcemia of immobilization and reducing the associated bone loss. (Choice A) Approximately 40% of circulating calcium is bound to proteins (predominantly albumin). Hypoalbuminemia will lower the total serum calcium level; therefore, measured calcium levels are corrected upward based on the extent of hypoalbuminemia. Conversely, hyperalbuminemia is associated with an increase in total calcium. In either case, the ionized fraction is unaffected, and patients will not have calcium-related symptoms directly related to the change in albumin levels. (Choices C and F) Hypercalcemia in malignancy can be due to osteolytic metastasis, secretion of PTH-related protein (PTHrP), or increased formation of 1,25-dihydroxyvitamin D. This patient's PTHrP and 1,25-dihydroxyvitamin D levels are low. (Choice D) This patient's PTH level is suppressed, which makes primary hyperparathyroidism unlikely. (Choice E) Acute rhabdomyolysis causes hypocalcemia due to precipitation of calcium and phosphorus in damaged muscles. Hypercalcemia can occur due to remobilization of calcium during the diuretic/recovery phase of the illness, often with concurrent hyperphosphatemia. However, this patient recovered from rhabdomyolysis several weeks before the onset of hypercalcemia. Educational objective: Hypercalcemia can occur in prolonged immobilization due to increased osteoclastic activity, especially in individuals with a high baseline rate of bone turnover. Bisphosphonates can reduce this hypercalcemia and prevent bone loss. References: Immobilization induced hypercalcemia. (http://www.ncbi.nlm.nih.gov/pubmed/27252745)

A 17-Year-Old Boy Is Brought to the Emergency Department Following