Abstract #1403692: Discrepancy Between Dual-Energy X-ray Absorptiometry and Quantitative Computed Tomography in Analyzing Bone Mineral Density in a Patient with Primary Hyperparathyroidism, Fractures and Degenerative Joint Disease - A Case Report and Review of Literature

Abstract

Primary hyperparathyroidism is associated with lower bone mineral density (BMD). Dual-energy x-ray absorptiometry (DXA) is the gold standard to measure BMD and a T-score of less than -2.5 is an indication for parathyroidectomy. However, DXA has limitations in skeletal evaluation of patients with primary hyperparathyroidism and degenerative joint disease (DJD). The use of quantitative computed tomography (QCT) should be considered for these patients to accurately assess their BMD to guide proper management. 87-year-old female with a past medical history of primary hyperparathyroidism and DJD. She has a previous history of two left femoral fractures and underwent surgical repair. She was not considered for parathyroidectomy based on her age, serum calcium, and absence of renal and skeletal indications for surgery given that her BMD only reveals osteopenia. Patient experienced sudden-onset low back pain and MRI of the spine revealed L1 compression fracture and diffuse DJD. QCT showed severe osteoporosis with BMD of 21.8 mg/c (T-score equivalent of -5.64) while her DXA only showed osteopenia on the lumbar spine and right femoral neck with T-score of -1.4 and -2.3, respectively. Based on the history of vertebral fracture and QCT result, patient was referred for parathyroidectomy. Osteoporosis is a degenerative disease of the bone characterized by low BMD which predisposes patients to low-impact, fragility fractures. Regular assessment of BMD in patients with primary hyperparathyroidism is beneficial to evaluate the need for parathyroidectomy. While current guidelines suggest the use of DXA to assess BMD, it does not always reflect the accurate state of the bones. From the review of the literature, the difference of T-scores between DXA and QCT is due to an artifact from arthritic changes and degenerative disease. DXA evaluates cortical bone and findings can be influenced by degenerative changes and facet joint hypertrophy, which is strongly associated with the overestimation of the BMD. QCT, on the other hand, evaluates trabecular and cortical bone separately and is not affected by arthrosic changes and vascular calcifications. Clinicians should be aware of the discrepancy and should consider QCT instead of DXA for screening and diagnosing of osteoporosis in patients with primary hyperparathyroidism, DJD and history of fractures. If the skeletal assessment was done by QCT and not DXA, parathyroidectomy could have been done earlier preventing her vertebral fracture. Therefore, we suggest adding the option to perform QCT instead of DXA for the skeletal assessment of patients with asymptomatic hyperparathyroidism who has DJD.