WBR0228

Author	[[PageAuthor::Mugilan Poongkunran M.B.B.S [1]]]
Exam Type	ExamType::USMLE Step 3
Main Category	MainCategory::Inpatient Facilities
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A 20 yr old male was admitted to ICU following a motor vehicle accident. He sustained a cervical vertebrae translocation, which resulted in quadriplegia. He was put on ventilator and PEG tube. His vitals were normal and the patient was stabilized. After 2 weeks in ICU, his biochemical parameters shows a serum calcium of 12.8 mg/dl, a PTH level of 12pg/ml (N: 10-65pg/ml), a 25-hydroxyvitamin D level of 24mcg/ml (N 18-68 mcg/ml) and 1,25 dihydroxyvitamin D level of 15ng/L(N: 15-60ng/L). A repeat calcium level was 13.3mg/dl, with phosphorus level of 3.2mg/dl, albumin level 2.5 g/dl and ionized calcium level of 6.6mg/dl (N: 4-5.6mg/dl). What is the most likely cause of patient’s hypercalcemia?]]
Answer A	AnswerA::Immobilization
Answer A Explanation	[[AnswerAExp::Correct : Immobilization causes increased bone resorption and decreased bone formation and high serum calcium lowers PTH levels and subsequently the vitamin D levels because PTH stimulates the 1α hyroxylase activity in the kidneys.]]
Answer B	AnswerB::Primary hyperparathyroidism
Answer B Explanation	[[AnswerBExp::Incorrect : The level of PTH is within normal limits; hence they are unlikely to be the cause in this patient.]]
Answer C	AnswerC::Paraproteinemia
Answer C Explanation	[[AnswerCExp::Incorrect : Patient has elevated ionized and total calcium. Hence paraproteinemia is unlikely. Proteins bind with calcium and cause spuriously elevated total calcium levels. Corrected calcium levels should be measured. For every 1 g/dl decrease in albumin below 4, we should add 0.8 mg to the total calcium levels.]]
Answer D	AnswerD::Vitamin D toxicity
Answer D Explanation	[[AnswerDExp::Incorrect : The level of Vitamin D is within normal limits; hence they are unlikely to be the cause in this patient]]
Answer E	AnswerE::Lab error
Answer E Explanation	AnswerEExp::'''Incorrect''' : Patient has elevated ionized and total calcium. Hence lab error is unlikely in this patient.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient has a characteristic presentation of hypercalcemia because of immobilization. Immobilization causes increased bone resorption and decreased bone formation (uncoupling of bone turn over). The mechanism is unknown and it happens in patients with very high bone turnover like adolescents and old people with Paget’s disease. High serum calcium lowers PTH levels and subsequently the vitamin D levels because PTH stimulates the 1α hyroxylase activity in the kidneys. Treatment is similar to other causes of hypercalcemia. IV hydration followed by furosemide to calcium excretion. Bisphosphonates (e.g., pamidronate) are particularly useful for reducing the bone resoption in patients with high bone turn over. Calcitonin, glucocorticoids, calcimimetics, and dialysis are used for severe or refractory cases. Avoid thiazide diuretics, which cause tubular reabsorption of calcium. Educational Objective: References: ]]
Approved	Approved::Yes
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