EPIDEMIOLOGY AND CLINICAL-FEATURES OF OSTEOPOROSIS IN YOUNG INDIVIDUALS

Due to the lack of epidemiologic data on osteoporosis in the young, we identified all 22 Olmsted County, MN, residents aged 20-44 years when first diagnosed with established osteoporosis in 1976-1990. The overa ll age- and sex-adjusted incidence rate was 4.1 per 100,000 person-yea rs (95% CI 2.4-5.9) with a female to male ratio of age-adjusted rates of 1.2:1. The majority represented secondary osteoporosis (12 steroid- induced, 3 postmenopausal, 2 delayed puberty, 2 anticonvulsant-induced , 2 gastrointestinal disease, 2 alcoholism, 1 anorexia nervosa, and 7 other etiologies; some individuals had more than one factor present) b ut two had idiopathic osteoporosis (incidence 0.4 per 100,000 person-y ears, 95% CI 0-0.9). To further characterize the patients with idiopat hic osteoporosis, we also reviewed the entire Mayo Clinic experience w ith such patients from 1976 to 1990, regardless of residency. A total of 56 patients (30 female/26 male) were identified with a median age a t diagnosis of 34 years. Only 8% were hypercalciuric at presentation. There was a preponderance of cancellous bone fractures (vertebral 81%, rib 37%, wrist 13%), although 13% did have hip fractures. Transiliac bone biopsies were available in 18 patients. As compared to age- and s ex-matched controls, the osteoporotic subjects had a significant reduc tion in trabecular bone volume, cortical thickness, and mean wall thic kness, the latter suggesting an abnormality in osteoblast function in these individuals. These studies, therefore, define for the first time the incidence and etiology of osteoporosis in young individuals and p rovide further clinical and histomorphometric definition of patients w ith idiopathic osteoporosis. Our data suggest that impaired osteoblast function may be a common finding in these patients, although the etio logy of this abnormality remains to be determined.