Aims: Osteoporosis is uncommon in premenopausal women, and most cases have a secondary cause. Women with osteoporosis and no known secondary cause are said to have idiopathic osteoporosis (IOP). We aimed to estimate the proportion of premenopausal women seen in our referral center with IOP as opposed to secondary osteoporosis, to describe their clinical characteristics, to compare women with a low-trauma fracture history with those with low bone mineral density (BMD) alone, and to estimate the frequency of bisphosphonate use.
Methods: We reviewed medical records from all premenopausal women evaluated for osteoporosis or low BMD in our center during 2005. We included premenopausal women diagnosed on the basis of low-trauma fracture, low BMD or both (Z score < or= -2.0 or T score < or = -2.5), or both.
Results: Among these patients (n = 61; mean age 37 +/- 8), 57 (93%) were Caucasian, 34 (57%) had a family history of osteoporosis, and 26 (43%) had used bisphosphonates. The most common secondary causes were amenorrhea (34%, n = 21), anorexia nervosa (16%, n = 10), and glucocorticoid exposure (13%, n = 8). After exclusion of secondary causes, 39% (24 of 61) of the entire group and 48% (14 of 29) of the fracture group were thought to have IOP. Women with a known secondary cause had lower BMD Z scores at the spine and hip than those with IOP. Women with low BMD and no fractures had shorter stature and weighed less than those with fractures, but overall differences between the groups were not statistically significant. Bisphosphonates had been prescribed for 38% (11 of 29) of women with a fracture history and 47% (15 of 32) of women with low BMD and no fractures.
Conclusions: Our findings suggest that IOP is common among premenopausal women with osteoporosis or low BMD evaluated at a referral center. The smaller stature of women diagnosed only on the basis of BMD criteria raises the question of whether their areal BMD measurements are spuriously low because of smaller bone size. The high proportion of premenopausal women who had been prescribed oral bisphosphonates for low BMD measurements is of concern, as such women are likely to be at low short-term risk of fracture, and a more conservative approach to therapy is preferable in this group.