Regional migratory osteoporosis: a pathogenetic hypothesis based on three cases and a review of the literature.

Regional migratory osteoporosis (RMO) is a migrating arthralgia of the weight-bearing joints of the lower limb which mainly affects middle-aged males. Its aetiology is unknown. The association of RMO with generalised osteoporosis has recently been reported. A concurrent systemic osteoporosis was also reported in some cases of transient osteoporosis of the hip (TOH), a disorder closely related to RMO. In its turn, TOH is considered a reversible stage of avascular necrosis of the hip (AVN), and the aetiopathogenesis of both of them remains strongly debated. We report three cases of RMO associated with generalised severe idiopathic osteoporosis. Three men, in the fourth and fifth decades of life, complained of at least four episodes of arthralgia in the lower limbs, with a migratory pattern, radiographic focal osteoporosis and final clinical resolution. The most striking common feature of these patients was the presence of a severe systemic osteoporosis with a prevailing trabecular involvement. We suggest that a prolonged or exaggerated activation of regional acceleratory phenomena (RAP) is the cause of transient osteoporosis. Bone tissue microdamage due to osteoporosis may be the most frequent noxious stimulus that turns RAP on, and, bone tissue microfracture is the most prevalent consequence. When this pathogenetic pathway is activated, the progression from focal osteoporosis and bone marrow oedema to avascular necrosis is associated with the amount of structural damage.