A 16-year-old boy is evaluated by the medical team in the intensive care unit. He was admitted 3 weeks ago following a motor vehicle accident. The patient sustained a C5-C6 fracture with dislocation, which resulted in quadriplegia. He currently has a tracheostomy tube and requires mechanical ventilation, and is being fed by a percutaneous endoscopic gastrostomy tube. A week ago, the patient was diagnosed with ventilator-associated pneumonia, which is being treated with piperacillin-tazobactam. His mother says that before his injury he was trying to "build up his muscles" by drinking protein shakes and taking creatine supplements. Medical history is otherwise unremarkable. The patient's mother has Graves disease and his father has hypertension. He has no siblings. Blood pressure is 124/70 mm Hg and pulse is 64/min. Coarse crackles are heard at the right lung base. Laboratory results are as follows: Repeat testing confirms these values. Ionized calcium level is 6.6 mg/dL (normal: 4-5.6 mg/dL). Which of the following is the most likely cause of this patient's hypercalcemia?
A)Enteral nutrition
B)Granulomatous lung infection
C)Hyperthyroidism
D)Immobilization
E)Paraproteinemia

Question

A 16-year-old boy is evaluated by the medical team in the intensive care unit.  He was admitted 3 weeks ago following a motor vehicle accident.  The patient sustained a C5-C6 fracture with dislocation, which resulted in quadriplegia.  He currently has a tracheostomy tube and requires mechanical ventilation, and is being fed by a percutaneous endoscopic gastrostomy tube.  A week ago, the patient was diagnosed with ventilator-associated pneumonia, which is being treated with piperacillin-tazobactam.  His mother says that before his injury he was trying to "build up his muscles" by drinking protein shakes and taking creatine supplements.  Medical history is otherwise unremarkable.  The patient's mother has Graves disease and his father has hypertension.  He has no siblings.  Blood pressure is 124/70 mm Hg and pulse is 64/min.  Coarse crackles are heard at the right lung base.  Laboratory results are as follows:  Repeat testing confirms these values.  Ionized calcium level is 6.6 mg/dL (normal: 4-5.6 mg/dL).  Which of the following is the most likely cause of this patient's hypercalcemia?
A)Enteral nutrition 
B)Granulomatous lung infection 
C)Hyperthyroidism 
D)Immobilization 
E)Paraproteinemia

Quizplus · Accepted Answer

Explanation: 11ec2b69_c135_9f9d_8f63_652c3dfd221c_MD0005_00 This patient has parathyroid hormone (PTH)-independent hypercalcemia (ie, elevated serum calcium, suppressed PTH). His albumin-corrected calcium (measured calcium + 0.8 x [4 - albumin]) is 14.0 mg/dL. In the setting of critical illness and acute quadriplegia, this is most likely due to immobilization. Hypercalcemia due to immobilization is typically seen in patients with very high bone turnover (eg, adolescents, Paget disease). When these patients are immobilized, bone resorption is further increased and bone formation is decreased, leading to release of calcium from bone stores. 25-hydroxyvitamin D levels are usually normal, although 1,25-dihydroxyvitamin D levels may be low due to the suppressed PTH (PTH stimulates conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D in the kidneys). Management of hypercalcemia due to immobilization is similar to that for other hypercalcemic states. Bisphosphonates are useful in decreasing bone resorption and may preserve bone mass in patients who are immobilized for extended periods. (Choice A) Hypercalcemia was seen previously with total parenteral nutrition (TPN) due to excessive calcium and vitamin D in the TPN solution. However, enteral feedings (and contemporary TPN solutions) rarely cause hypercalcemia. (Choice B) Granulomatous disorders (eg, sarcoidosis, tuberculosis) can cause hypercalcemia due to extrarenal production of 1,25-dihydroxyvitamin D. This patient's 1,25-dihydroxyvitamin D level is low, making granulomatous disease less likely. (Choice C) Hypercalcemia can be seen in thyrotoxicosis but is usually mild. This patient has no tachycardia or other signs of hyperthyroidism. (Choice E) Paraproteinemia (eg, monoclonal gammopathy) can cause an elevated total serum calcium due to an increase in the bound calcium fraction, but ionized calcium is normal. This patient's ionized calcium is high, and paraproteinemias are uncommon in young, otherwise healthy individuals. Educational objective: Extended immobilization can cause hypercalcemia due to release of calcium from bones. This is most common in patients with increased bone turnover (eg, adolescents, Paget disease). Bisphosphonates can decrease bone turnover and preserve bone mass. References: Investigation of hypercalcemia. (http://www.ncbi.nlm.nih.gov/pubmed/22569596) Immobilization induced hypercalcemia. (http://www.ncbi.nlm.nih.gov/pubmed/27252745)

A 16-Year-Old Boy Is Evaluated by the Medical Team in the Intensive