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Abnormal BMD image shows evidence of hip pain
A 62-year-old female was seen in the endocrine clinic for the routine management of hypothyroidism after undergoing a thyroidectomy to treat a toxic follicular adenoma and osteopenia. The patient was postmenopausal with a history of persistently low vitamin D and poor calcium intake.
Her bone mineral density exam performed every 2 to 4 years had shown stable osteopenia between 2002 and 2012 until her present exam in 2014. A Norland XR-800 densitometry was performed of the hip and spine that showed a lumbar spine density (L2-L4) of 1.12 g/cm2 (T-score: 0.11) with the femoral neck density of 0.854 g/cm2 (T-score: –1.13). Compared with 2012, there was an insignificant 0.6% decrease in the lumbar spine but a significant 5.8% decrease in the femoral neck BMD.
Stephanie L. Lee
Visual inspection of the hip images obtained with the BMD was performed to determine whether the change in BMD was due to the position of the hip during the exam. The position was appropriate and similar to the prior two exams in 2010 and 2012 (Figure 1). Examination of the images showed a site of calcification superior to the greater trochanter on the left that was apparently increasing in size and density over time. This ectopic calcification did not influence the BMD evaluation.
Figure 1: DXA images. The left hip DXA images from 2010, 2012 and 2014. The leg is in the same orientation in all three images. The femoral neck box is located in a similar location where the femoral neck is the narrowest with the lowest density. A calcified mass is seen and apparently enlarging superior to the greater trochanter (red arrow). This ectopic calcification did not affect the BMD measurements. Reprinted with permission from: Stephanie L. Lee, MD, PhD.
Increasing hip pain
The patient denied any trauma to that area but had increasing bilateral hip pain, especially over the left hip in the past 5 years requiring daily nonsteroidal anti-inflammatory drug therapy. The pain awakens her at night and prevents her from doing normal daily activities.
Although she was taking vitamin D 50,000 units once each month, she had stopped her calcium supplements because of constipation and ceased her daily walking because of the hip pain over the prior 1 to 2 years.
Radiographs of the left hip (Figure 2) and pelvic radiographs were obtained. A heterotopic calcification/ossification was noted superior to the greater trochanter on the left, but not the right, that was not present on a prior hip radiograph that was obtained for hip pain 5 years before.
An orthopedic evaluation confirmed calcific tendinitis that was treated with a glucocorticoid injection and physical therapy. Secondary causes of bone loss were negative, showing a normal thyroid-stimulating hormone 2.14 mIU/mL (normal, 0.35-4.9) on levothyroxine therapy, 25-hydroxyvitamin D 36 ng/mL (normal, 30-100), calcium 9.6 mg/dL (normal, 8-10.5) and parathyroid hormone 48 pg/mL (normal, 10-80).
Figure 2: Left hip radiograph. Comparison of the left hip radiography from 2009 and 2014 showed the interval development of a heterotopic calcification/ossification just superior to the greater trochanter. This is consistent with calcific tendinitis.
She stopped smoking more than 10 years before, did not drink alcohol and denied problems with balance or vision. She did not have a family history of osteoporosis or fracture at an older age. The patient was instructed to resume calcium replacement with a women’s multivitamin that contains vitamin D 1,000 units and elemental calcium 500 mg at breakfast plus one calcium with vitamin D 500 mg with dinner and increase her weight-bearing activity as tolerated. Since she had mild osteopenia, it was recommended to repeat her BMD in 2 years.
Using DXA
DXA is the recommended method to measure a patient’s BMD to asses fracture risk. The radiation exposure is much less than a standard chest radiograph and, therefore, the images are not of diagnostic quality.
Certain conditions make a DXA scan less reliable, including lumbar spinal deformity (scoliosis), calcified blood vessels, degenerative arthritis with osteophytes, patient movement, operator error in determining location of measurement and poor femur placement during the exam.
There are several sites to measure the hip BMD. The Ward’s triangle is the most sensitive location to measures loss of BMD but also the location is very subjective and determined by the technician. It is the least reproducible of the hip measurements and not recommended for monitoring of BMD.
The main purpose of the DXA scan image is to determine whether the patient is positioned correctly. There is a disclaimer next to the images saying “not for diagnostic purposes.” The DXA image are checked by the technician before the exam is completed, but it is important that if an unexpected result is reported, then the clinician should examine the images.
The femur is positioned correctly when the femoral shaft is parallel to the edge of the picture with a 15° to 25° of internal rotation. This is achieved usually with a soft foam block placed between the patient’s thighs. The position of the femoral neck box (Figure 1) is at the narrowest and lowest density section of the femoral neck. This is usually about half way between the femoral neck and the trochanter.
The images should be evaluated for artifacts such as surgical clips, metal from a zipper, coins, clips or heterotopic calcification. All of these artifacts will spuriously elevate the BMD. If there is a concern for compression fractures or heterotopic calcification, then a diagnostic X-ray should be ordered.
In this case, the review of the images did not explain her bone loss but did show structural evidence of her hip pain that is being treated. Her bone loss is very likely related to decrease compliance with calcium and immobilization because of her hip pain.