An unusual case of diffuse focal osteolysis with disseminated osteoclastosis.

We report the unusual case of a 31-year-old woman referred for inflammatory pain of the long bones associated with diffuse focal osteolysis, elevated erythrocyte sedimentation rate (ESR) and hypercalcemia. Corticosteroid therapy produced dramatic symptomatic improvement, and biological parameters returned to normal. Biochemical markers of bone remodeling, particularly those of resorption, were strikingly elevated. Parathyroid hormone, parathyroid hormone-related protein, nephrogenous cyclic adenosine monophosphate and calcitriol levels were normal. Investigations for infectious disease and malignancy were negative. The histology of the lesions consisted of cortical osteolysis caused by intense osteoclastic resorption, with several foci of osteogenesis, without malignant cells. The patient died 9 months after the onset of symptoms, following a "malignant" course: severe hypercalcemia, extension of lytic bone lesions and spontaneous fractures. To our knowledge, such a peculiar picture with quite unusual radiologic findings, disseminated focal cortical lesions and a progressive course, without evidence for a tumoral process, has never been described. This case suggests either the presence of an unknown systemic osteoclast-activating factor from an occult tumor or a primary malignant hyperosteoclastosis.