Rheumatoid arthritis associated with osteopetrosis.

Osteopetrosis is an inherited disorder characterized by reduced bone resorption. We here report a rare case of osteopetrosis associated with rheumatoid arthritis. The patient was diagnosed as autosomal dominant osteopetrosis type II in his youth and developed rheumatoid arthritis at 42 years of age. In spite of the severe inflammation and rapid progression of cartilage destruction, the progression of bone erosion was slow in this patient.