Idiopathic osteoporosis: a heterogeneous entity.

DEFINITION: Idiopathic osteoporosis refers to the development of osteopenia and fractures with minimal or no trauma in otherwise young, healthy individuals who are not postmenopausal or have other, identifiable secondary causes of osteoporosis. EPIDEMIOLOGY: It is a relatively rare disorder, with an incidence of 0.4 cases per 100,000 person-years. It appears to affect both sexes equally and results primarily in the development of trabecular bone fractures such as vertebral compression fractures and Colles' fractures, although hip fractures are also seen. PATHOPHYSIOLOGY: The disease may be temporally related to pregnancy and/or lactation in some patients, although it is unclear whether pregnancy plays a pathophysiological role or, more likely, simply leads to the clinical presentation of the disease in individuals who are already affected. Various pathophysiological abnormalities have been described in these patients, including hypercalciuria, abnormalities in vitamin D metabolism, and in the production of insulin-like growth factor I and interleukin 1. Findings on bone biopsy have been variable, with some patients having evidence of a defect in osteoblast function, whereas others having evidence for increased bone resorption. TREATMENT: No specific therapy has been proven to be effective in these patients. However, an individualized approach based on an assessment of bone turnover may be reasonable and may decrease the bone loss and subsequent fracture risk.