A 48-year-old man comes to the office due to generalized bone pain. The patient has a history of Crohn disease and underwent extensive small bowel resection several months ago. His current medications are mesalamine and infliximab, and he has not used glucocorticoids recently. The patient has a sedentary lifestyle and spends most of his time watching television. Physical examination shows bony tenderness of the lower spine, pelvis, and lower extremities. There is mild weakness of proximal limb muscles. Radiographs reveal diffuse osteopenia of the spine and pseudofractures in both femoral necks. Which of the following sets of laboratory findings is most consistent with this patient's current condition?

Question

A 48-year-old man comes to the office due to generalized bone pain.  The patient has a history of Crohn disease and underwent extensive small bowel resection several months ago.  His current medications are mesalamine and infliximab, and he has not used glucocorticoids recently.  The patient has a sedentary lifestyle and spends most of his time watching television.  Physical examination shows bony tenderness of the lower spine, pelvis, and lower extremities.  There is mild weakness of proximal limb muscles.  Radiographs reveal diffuse osteopenia of the spine and pseudofractures in both femoral necks.  Which of the following sets of laboratory findings is most consistent with this patient's current condition?

Quizplus · Accepted Answer

11ec25c8_d3cf_2eea_bc81_c1371afe7d28_MD0003_00 This patient with Crohn disease who underwent extensive bowel resection now has bone pain, proximal muscle weakness, and x-rays revealing osteopenia and pseudofractures (cortical infarction/insufficiency fractures traversing part of the bone). This presentation suggests osteomalacia, characterized by reduced mineralization of osteoid at bone-forming sites. Osteomalacia is common in patients with malabsorptive disorders (eg, Crohn disease with bowel resection) due to chronic deficiency of vitamin D. Although patients can be asymptomatic, many develop generalized bone pain (including at the sites of pseudofractures) and muscle weakness. Alkaline phosphatase levels are almost always elevated, reflecting increased bone remodeling. Vitamin D deficiency leads to decreased intestinal calcium (leading to hypocalcemia) and phosphorus absorption (leading to hypophosphatemia). Hypocalcemia and low vitamin D levels trigger increased parathyroid hormone (PTH) secretion (ie, secondary hyperparathyroidism), which increases bone resorption and renal calcium reabsorption. PTH also increases urinary phosphate excretion, which further worsens hypophosphatemia. Therefore, the net effect is increased PTH, very low serum phosphorus, and mildly low or low-normal serum calcium. increases bone resorption and renal calcium reabsorption Although 25-hydroxyvitamin D levels are low (decreased total body stores), levels of 1,25-dihydroxyvitamin D are variable because it is produced in the kidneys in response to PTH. X-ray findings seen with osteomalacia include cortical thinning, concave vertebral bodies (codfish vertebrae), and pseudofractures (Looser zones). Looser zones (Choice A) Increased calcium, low phosphate, and increased PTH levels are seen in patients with primary hyperparathyroidism. Although hyperparathyroidism can cause osteopenia, most patients are asymptomatic or have minor, nonspecific symptoms (eg, fatigue, constipation). Pseudofractures, diffuse bony tenderness, and history of intestinal resection more strongly suggest osteomalacia. (Choice B) Low calcium, increased phosphate, and low PTH levels are seen in patients with hypoparathyroidism. Symptoms typically relate to hypocalcemia (eg, carpal spasm, perioral paresthesia), and osteopenia would be unexpected. (Choice D) Normal levels of calcium, vitamin D, and PTH would be seen in osteoporosis, which would cause decreased bone density but would not cause generalized bone pain/tenderness, muscle weakness, or pseudofractures. (Choice E) Osteolytic bone metastases release calcium and phosphorus from bone, suppressing PTH secretion. A compensatory increase in fibroblast growth factor 23 may subsequently normalize serum phosphorus. X-rays would show irregular lytic lesions rather than symmetric pseudofractures. Educational objective: Intestinal malabsorption with chronic vitamin D deficiency can lead to osteomalacia, which is characterized by reduced mineralization of osteoid. Symptoms include bone pain and muscle weakness. Laboratory findings include hypocalcemia, hypophosphatemia, increased parathyroid hormone, and elevated alkaline phosphatase. X-ray findings include cortical thinning, concave vertebral bodies, and pseudofractures. References: Osteomalacia as a result of vitamin D deficiency. (http://www.ncbi.nlm.nih.gov/pubmed/22525844)

A 48-Year-Old Man Comes to the Office Due to Generalized