A 65-year-old woman comes to the office to discuss bone density test results. She has had chronic low back pain since a motor vehicle collision 25 years ago but otherwise feels well and has had no recent injuries. Medical history is unremarkable. The patient does not use tobacco or alcohol.
Vital signs are normal. BMI is 20 kg/m². Examination shows decreased range of motion in the lumbar spine with no focal tenderness. Lower extremity neurologic examination is normal, and straight-leg raising test is negative bilaterally.
Serum chemistry panel, complete blood count, and 25-hydroxyvitamin D level are normal. DXA reveals a T-score of +0.2 in the lumbar spine and −2.7 at the right hip.
Which of the following is the most likely reason for the discordant DXA results in this patient?

Question

Quizplus · Accepted Answer

11ec193a_9944_4b5d_853d_dffc83f112c4_MD0002_00 This patient's DXA scan reveals a T-score ≤−2.5 at the hip, which is consistent with osteoporosis. However, her DXA results also show a significant discordance, with a much higher bone density at the lumbar spine. In addition, the patient has long-standing, posttraumatic back pain associated with decreased range of motion in the lumbar spine. This presentation suggests osteoarthritis, likely with extensive osteophyte formation. Osteophytes and other abnormal calcifications (eg, syndesmophytes, vascular calcifications) can increase local x-ray absorption and give a misleadingly high DXA result. Treatment decisions in osteoporosis should usually be made according to the lowest bone density measurement because bone density at any location correlates with fracture risk for that location. If necessary, density at additional sites (eg, distal radius) may be measured. This patient's lowest measured density is diagnostic for osteoporosis, so she should be offered appropriate antiresorptive therapy (eg, bisphosphonates). (Choice A) Avascular necrosis of the hip can lead to altered bone density and collapse of the articular surface of the femoral head. However, most patients have significant hip pain. This patient has no symptoms or risk factors (eg, glucocorticoid use, sickle cell disease) for this condition. (Choice B) Hyperparathyroidism is a common secondary cause of osteoporosis and often causes greater loss of cortical (forearm, hip) than trabecular (vertebrae) bone. However, it would usually be associated with hypercalcemia. (Choice C) Osteolytic bone metastasis can cause a focal decrease in bone density. However, this patient has no hip pain, hypercalcemia, or history of cancer to suggest osteolytic lesions. (Choice D) Paget disease of bone affecting the hip would usually cause a focal increase in density. In addition, most patients have an elevated serum alkaline phosphatase level. Educational objective: Treatment decisions in osteoporosis should usually be made according to the lowest bone density measurement. Osteophytes and other abnormal calcifications can increase local x-ray absorption and give a misleadingly high DXA result. __________

A 65-Year-Old Woman Comes to the Office to Discuss Bone