A 56-year-old woman comes to the office for a follow-up visit. She has chronic kidney disease due to systemic lupus erythematosus (SLE) and nonsteroidal anti-inflammatory drug use. Medical history is notable for recurrent kidney stones, and the patient experienced natural menopause at age 49. Her only current medication is hydroxychloroquine. The patient quit smoking 10 years ago when she was diagnosed with SLE. Family history is noncontributory. Laboratory results are as follows: DXA bone densitometry scan shows a T score of -2.5 at the lumbar spine, which is consistent with osteoporosis. Which of the following is the most likely cause of this patient's hypercalcemia?

Question

A 56-year-old woman comes to the office for a follow-up visit.  She has chronic kidney disease due to systemic lupus erythematosus (SLE) and nonsteroidal anti-inflammatory drug use.  Medical history is notable for recurrent kidney stones, and the patient experienced natural menopause at age 49.  Her only current medication is hydroxychloroquine.  The patient quit smoking 10 years ago when she was diagnosed with SLE.  Family history is noncontributory.  Laboratory results are as follows:  DXA bone densitometry scan shows a T score of -2.5 at the lumbar spine, which is consistent with osteoporosis.  Which of the following is the most likely cause of this patient's hypercalcemia?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d3b6_015f_bc81_0dd80d5edb45_MD0003_00 Causes of hypercalcemia can be categorized on the basis of parathyroid hormone (PTH) levels as PTH-dependent or PTH-independent: PTH-independent hypercalcemia (suppressed PTH) is usually due to malignancy, vitamin D toxicity, or extrarenal conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D in granulomatous diseases (eg, sarcoidosis) (Choices F and G). PTH-dependent hypercalcemia (elevated or inappropriately normal PTH) is usually due to primary hyperparathyroidism (PHPT). This patient has hypercalcemia with an elevated PTH level, suggesting PHPT. Normally, elevated plasma calcium suppresses PTH secretion. However in PHPT, PTH secretion from autonomously functioning parathyroid adenomas or parathyroid hyperplasia is not suppressed. Most patients with PHPT present with mild, asymptomatic hypercalcemia, but potential clinical features include nephrolithiasis, osteoporosis, nausea, constipation, and neuropsychiatric symptoms ("stones, bones, abdominal moans, psychic groans"). Serum phosphorus is often normal but can be low in moderate-to-severe PHPT. suppresses PTH secretion (Choice A) Secondary hyperparathyroidism is characterized by increased secretion of PTH in response to hypocalcemia. It is a common finding in chronic kidney disease due to inadequate phosphate excretion and low 1,25-hydroxyvitamin D levels. Serum phosphorus will be high and calcium will be low or low-normal. Long-standing secondary hyperparathyroidism can lead to autonomous PTH secretion (tertiary hyperparathyroidism), but this is typically seen in patients with end-stage renal disease (eg, on hemodialysis) and would be very unusual with a creatinine of 1.6 mg/dL. It is associated with very high PTH levels. (Choice B) Hypercalcemia of malignancy is usually due to secretion of PTH-related protein and is characterized by severe hypercalcemia (typically >14 mg/dL) and a suppressed PTH level. (Choice C) Milk-alkali syndrome is caused by excessive ingestion of calcium and absorbable alkali (eg, calcium-containing antacids). Calcium would be elevated, but PTH would be suppressed. (Choice D) Circulating levels of calcium and PTH are normal in primary osteoporosis. Educational objective: Primary hyperparathyroidism is characterized by autonomous secretion of parathyroid hormone from parathyroid adenomas or parathyroid hyperplasia. Most patients have mild, asymptomatic hypercalcemia, but potential clinical features include nephrolithiasis, osteoporosis, nausea, constipation, and neuropsychiatric symptoms. References: Primary hyperparathyroidism. (http://www.ncbi.nlm.nih.gov/pubmed/22982802) A practical approach to problems of hypercalcaemia. (http://www.ncbi.nlm.nih.gov/pubmed/19494663)

A 56-Year-Old Woman Comes to the Office for a Follow-Up