Pathogenesis and natural course of primary osteoporosis.

A new concept of the pathogenesis and natural course of osteoporosis is described, based on histomorphometric evaluation of iliac crest bone biopsies of 108 patients with untreated primary osteoporosis. It is suggested that primary osteoporosis spontaneously runs a three-phase course: during the initial period of negative bone balance, bone mass falls below the normal range; during the second phase bone mass remains consistently below age-related normal values; in the third phase restitution of osteoporosis is introduced by a positive bone balance. It is suggested that only about a quarter of patients with a skeletal mass below the age-related normal range have true primary osteoporosis; the remaining three-quarters may have secondary forms of osteoporosis where the underlying disease responsible for the bone loss had been missed before the osteoporosis was diagnosed.