Hemarthrosis revealing congenital factor XI deficiency.

Congenital factor XI deficiency (also known as the Rosenthal syndrome or hemophilia C) manifests as minor bleeding, usually after trauma or surgery. We report a case in which bilateral knee hemarthrosis was the first manifestation. The patient presented at 32 years of age with a 2-year history of mechanical pain and intermittent swelling in both knees. Knee aspiration recovered blood-tinged fluid. The laboratory workup showed severe factor XI deficiency. Replacement therapy with fresh frozen plasma was effective. Tests in the family showed factor XI deficiency in the patient's sister.