Assessment of lumbar bone mineral density using QCT and DXA for measurement of osteoporotic patients

Lumbar bone mineral density was assessed in 157 patients with primary osteoporosis and 75 with secondary osteoporosis by means of quantitative computed tomography (QCT) and dual energy X-ray absorptiometry (DXA). The ratio of young reference (YR) to the peak bone mass (%YR) and the ratio of age matched (%AM) to the same sex and age were used as indicators. %AM for primary osteoporosis was found in 100% in the age-group of 75 years or more by QCT and in the age-group of 60 years or more by DXA. %AM in the age-group between 50 and 70 was significantly lower by QCT than by DXA, revealing the existence of D/Q dissociation. %AM for secondary osteoporosis was less than 100% in any age-group by both QCT and DXA. D/Q dissociation was seen in cases of gastrointestinal malabsorption, liver dysfunction and post steroid treatment, but not in cases of thyroid dysfunction, parathyroid dysfunction and sex hormone abnormality. Patients with rheumatoid arthritis had the same %AM as control persons. These results suggest that the combination of QCT and DXA has the potential for assessing underlying diseases in osteoporosis. (N.K.)