Caveats in diagnosis of osteoporosis

With increasing life expectancy the prevalence of osteoporosis is on rise and it poses a major public health issue. Bone Mineral Density (BMD) measurement by Dual Energy X-ray Absorptiometry (DEXA) is now widely available and is considered as a gold standard. Bone density measured by DEXA is obtained in grams/cm2, but in clinical practice these values are standardized and are expressed as T and Z scores. These scores are used for diagnosis and management of osteoporosis, but assessment with these scores alone is not without pitfalls. Any health care provider without complete awareness of these pitfalls could make an inappropriate diagnosis. Lumbar spine, proximal femur and wrist are the most common sites for BMD assessment. Degenerative changes a spine or hip, healed fractures, avascular necrosis, benign or metastatic bone forming lesions present as a false positive increase in BMD, while laminectomy defects and lytic lesions result in false negative decrease in BMD. Also the scores are dependent on age, gender, race and the machine used. Thus for follow up, it is important use the same scanner with same software version. In case of any discrepancy, it is necessary to compare the raw BMD values.