Hemophilia USMLE Notes

Hemophilia USMLE Notes & Mnemonics contains all the high-yield points you need to know.

Definition:

• Hemophilia: A group of hereditary genetic disorders that impair the body’s ability to control blood clotting. (Ref)

Types:

• Hemophilia A: Deficiency of factor VIII (8)
• Hemophilia B: Deficiency of factor IX (9), also known as Christmas disease

Epidemiology:

• X-linked recessive: Primarily affects males
• Female carriers: May have some degree of factor deficiency

Pathophysiology:

• Deficiency in clotting factors leads to impaired secondary hemostasis
• Does not affect platelet plug formation (primary hemostasis)

Clinical Features:

• Hemarthrosis: Bleeding into joints, especially knees, ankles, and elbows
• Easy bruising
• Prolonged bleeding: After trauma or surgery
• Spontaneous bleeding: In severe cases

Diagnosis:

• Prolonged aPTT: Normal PT/INR
• Low factor VIII or IX: Assayed to distinguish between Hemophilia A and B
• Normal bleeding time: Because primary hemostasis is intact
• Genetic testing: Can identify carriers and affected individuals

Treatment:

• Recombinant factor VIII or IX: Mainstay for Hemophilia A and B respectively
• Desmopressin (DDAVP): Can raise factor VIII levels in mild Hemophilia A
• Antifibrinolytics: Such as tranexamic acid for mucosal bleeding
• Avoid NSAIDs: Due to bleeding risk

Prophylaxis:

• Regular infusions of clotting factors to prevent bleeding

Complications:

• Hemophilic arthropathy: Chronic joint disease due to recurrent bleeding
• Inhibitor development: Antibodies against factor concentrates
• Transfusion-transmitted infections: Less common with recombinant factors

Mnemonics:

• “A for Eight“: Hemophilia A is a deficiency of factor VIII
• “B for IX“: Hemophilia B is a deficiency of factor IX

High-Yield Facts:

• Queen Victoria: Was a carrier of Hemophilia B, spreading it to the royal families of Europe
• Carrier mothers: 50% chance of passing the gene to sons, daughters have a 50% chance of being carriers
• Intracranial hemorrhage: A leading cause of death in hemophiliacs

Chart: Laboratory Findings in Hemophilia

Test	Hemophilia A	Hemophilia B	Normal
aPTT	Prolonged	Prolonged	Normal
PT/INR	Normal	Normal	Normal
Bleeding Time	Normal	Normal	Normal
Factor VIII level	Decreased	Normal	Normal
Factor IX level	Normal	Decreased	Normal

Additional Considerations:

• Gene therapy: An emerging treatment modality
• Prenatal diagnosis: For known carrier mothers
• Newer agents: Emicizumab, a bispecific monoclonal antibody, can bridge factor IXa and X to restore the function of missing factor VIII

Note: On the USMLE, be prepared to identify clinical scenarios suggestive of Hemophilia and understand the basic principles of management, including the avoidance of medications that can exacerbate bleeding.

Check other important USMLE Notes