A 40-year-old man comes to the office due to muscle and joint pains for 2 months. Review of systems is otherwise negative. The patient underwent Roux-en-Y gastric bypass surgery for obesity 2 years ago and has lost 40 kg (88 lb) since the surgery. Vital signs are normal. BMI is 28 kg/m². There is no pallor, lymphadenopathy, thyromegaly, or jaundice. Abdominal examination reveals no tenderness and no organomegaly. Muscle strength is 5/5, and no focal muscle tenderness is present. Deep tendon reflexes are normal. Laboratory results are as follows: Which of the following is the most appropriate next step in evaluation of this patient?

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11ec25c8_d127_3fb2_bc81_d718a8d07c11_MD0003_00 This patient has musculoskeletal pain and an elevated alkaline phosphatase level, suggesting increased bone turnover. Given his history of gastric bypass surgery, this most likely represents osteomalacia due to vitamin D deficiency. Patients who have undergone Roux-en-Y bariatric procedures can develop deficiency of fat-soluble vitamins due to reduced exposure of food to gastric acid, bacterial overgrowth, and voluntary restriction of certain foods. Roux-en-Y bariatric procedures Vitamin D deficiency reduces intestinal calcium absorption, leading to secondary hyperparathyroidism and renal phosphate wasting. The resulting hypophosphatemia causes impaired mineralization of newly deposited osteoid matrix. Although bone contours are generally normal, the newly formed bone is weak and prone to fracture. Initially, patients may be asymptomatic or have only nonspecific arthralgias and myalgias, but chronic deficiency can lead to proximal muscle wasting, gait abnormalities, and deformity of weight-bearing bones. Vitamin D deficiency should be confirmed with a serum 25-hydroxyvitamin D level, which reflects total body vitamin D stores. In contrast, 1,25-dihydroxyvitamin D primarily reflects parathyroid hormone levels and renal function and is not an accurate marker for deficiency. 1,25-dihydroxyvitamin D (Choice B) Primary biliary cholangitis (PBC) is an autoimmune disorder that causes significant elevations in alkaline phosphatase. Patients often have an abnormal antinuclear antibody test, although antimitochondrial antibodies have more utility. However, this disorder is uncommon in men, and the primary skeletal complication is osteoporosis, which is asymptomatic in the absence of fracture. Most patients with PBC have pruritus. (Choice C) Muscle pain with an elevated creatine kinase level is seen in various inflammatory and metabolic myopathies (eg, hypothyroid myopathy, statin myopathy). However, alkaline phosphatase, which reflects bone turnover, is usually normal, and this patient's history of gastric bypass makes osteomalacia more likely. (Choice D) The serum transferrin saturation can be used to screen for hemochromatosis. The liver disease in this disorder causes elevations in hepatic transaminases (eg, aspartate aminotransferase, alanine aminotransferase), but alkaline phosphatase is usually normal or only minimally elevated. (Choice E) Radionuclide bone scanning is useful in assessing Paget disease of bone, which can cause bone pain and an elevated alkaline phosphatase level but is uncommon at age <50 and usually causes localized bone symptoms rather than generalized muscle and joint pains. Educational objective: Vitamin D deficiency in patients who have had Roux-en-Y gastric bypass surgery (and other malabsorptive conditions) can lead to osteomalacia, presenting with diffuse musculoskeletal pain and an elevated alkaline phosphatase level. The diagnosis is confirmed by measuring serum 25-hydroxyvitamin D.

A 40-Year-Old Man Comes to the Office Due to Muscle