A 36-year-old woman comes to the office for evaluation of fatigue and generalized weakness for the past several weeks. She has had no appetite or weight changes, heat or cold intolerance, nausea or vomiting, or constipation. The patient's medical and family histories are unremarkable. Temperature is 36.7 C (98 F), blood pressure is 120/70 mm Hg, pulse is 76/min, and respirations are 14/min. Physical examination shows normal heart and lung sounds, an unremarkable abdominal examination, and no focal neurologic deficits. Laboratory results are as follows: Which of the following is the best next step in management of this patient?

Question

A 36-year-old woman comes to the office for evaluation of fatigue and generalized weakness for the past several weeks.  She has had no appetite or weight changes, heat or cold intolerance, nausea or vomiting, or constipation.  The patient's medical and family histories are unremarkable.  Temperature is 36.7 C (98 F), blood pressure is 120/70 mm Hg, pulse is 76/min, and respirations are 14/min.  Physical examination shows normal heart and lung sounds, an unremarkable abdominal examination, and no focal neurologic deficits.  Laboratory results are as follows:  Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

11ec25c8_d3c1_9a3a_bc81_73a9a0a2991e_MD0003_00 This patient with fatigue and weakness has symptomatic hypocalcemia. The first step in evaluating hypocalcemia is to measure the serum albumin level because hypoalbuminemia lowers total circulating calcium (measured on the basic metabolic profile) without affecting the metabolically active ionized calcium concentration (pseudohypocalcemia). If albumin is low, a corrected calcium level can be calculated (corrected calcium = [measured calcium] + 0.8 × [4.0 g/dL − serum albumin in g/dL]). Once true hypocalcemia is confirmed, the next step is to exclude causes such as massive blood transfusion, whereby citrate in transfused products binds to ionized calcium; and hypomagnesemia, which causes resistance to parathyroid hormone (PTH), the hormone that regulates minute-to-minute calcium concentrations. This patient has a normal albumin level, has not had any transfusions, and has a normal serum magnesium level. PTH is secreted in response to hypocalcemia, and hypocalcemia may develop when PTH secretion is insufficient. Therefore, patients with hypocalcemia should have a serum PTH level measured to exclude hypoparathyroidism (eg, autoimmune). This patient's PTH level is appropriately elevated given her hypocalcemia. In contrast to PTH, vitamin D regulates calcium levels over the longer term. Therefore, once hypoparathyroidism has been excluded, the next step is to measure a serum 25-hydroxyvitamin D level to rule out vitamin D deficiency. Common causes of vitamin D deficiency include inadequate dietary intake, inadequate sunlight exposure (which converts 7-dehydrocholesterol to vitamin D3 in the skin), and malabsorptive disorders. Levels of 1,25-dihydroxyvitamin D correlate with PTH activity rather than total body vitamin D stores and are not usually measured. (Choice A) Parathyroid scintigraphy is used to localize parathyroid adenomas in patients with hyperparathyroidism, which presents with hypercalcemia (not hypocalcemia). (Choice B) Fibroblast growth factor 23 (FGF23) lowers phosphate levels by decreasing intestinal absorption and increasing urinary excretion of phosphate. Elevated plasma FGF23 levels are seen in patients with phosphate retention and secondary hyperparathyroidism due to chronic kidney disease. (Choice C) Ectopic production of PTH-related peptide causes humoral hypercalcemia of malignancy; patients have hypercalcemia with suppressed PTH levels. (Choice D) A skeletal survey is used in evaluation of multiple myeloma, which typically causes hypercalcemia and primarily occurs in older adults. It has less utility in the evaluation of hypocalcemia. (Choice F) Alkaline phosphatase can be elevated in chronic or severe vitamin D deficiency but has low sensitivity; directly measuring vitamin D is preferred. Educational objective: Vitamin D deficiency can lead to hypocalcemia with an elevated parathyroid hormone level. Causes include inadequate dietary intake of vitamin D, inadequate sunlight exposure, or malabsorptive disorders. Evaluation includes measuring the serum 25-hydroxyvitamin D level. References: Hypocalcemia: updates in diagnosis and management for primary care. (http://www.ncbi.nlm.nih.gov/pubmed/22439169)

A 36-Year-Old Woman Comes to the Office for Evaluation of Fatigue