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Why can hemophilia cause bleeding into joints and muscles after minor injuries?

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blood disease Peripheral blood smear revealing histopathologic features indicative of a blast crisis in a case of chronic myelogenous leukemia (CML). Blast crisis occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells, or blast cells. This phase of CML is characterized by fever, weakness, and an enlarged spleen.

Hemophilia is a hereditary coagulation disorder caused by a deficiency in essential blood-clotting proteins, specifically factor VIII, factor IX, or factor XI.12

Under normal conditions, these proteins are required to form a stable fibrin clot to stop blood flow following tissue injury. In individuals with hemophilia, the absence of these factors prevents the blood from clotting effectively. Consequently, even minor injuries—which might otherwise be trivial—can lead to persistent, internal bleeding.31

This bleeding often manifests as hemarthrosis, or bleeding into the joints, as well as into muscles and soft tissues. Because the body cannot properly seal the damaged vessels, blood accumulates in these areas, causing swelling, pain, and, if left untreated, potential long-term damage such as chronic arthritis or loss of joint mobility. Management of these episodes typically requires the replacement of the missing clotting factor through medical infusion.142