A 4-year-old boy is brought to the emergency department by his mother with a painful, swollen knee for the past two hours. She reports that the knee swelled after he fell on the carpet while running in the house. She witnessed the fall and reports that it was not a bad fall. He has no known medical history and is not taking any medications. Physical examination is consistent with a hemarthrosis in the affected knee. X-rays are negative for fracture.
Which of the following is the most likely underlying cause of the patient's predisposition to this type of injury?
A) Factor VIII deficiency
This is a classic presentation of a patient with hemophilia. The patient is young (hemophilias are typically diagnosed early in life; hemophilia A at around 36 months, on average), the patient is male (hemophilias A and B are inherited in an X-linked recessive manner), and the patient presents with hemarthrosis of the knee (a classic example of a deep bleed that characterizes clotting factor disorders such as hemophilia). Hemophilia A is defined as factor VIII deficiency and is by far the most common hemophilia. The degree of bleeding correlates with severity of the hemophilia. More severe hemophilia may present with spontaneous bleeding, severe bleeding, or bleeding that occurs earlier in life and as early as birth. Patients with mild or moderate hemophilia may bleed as a result of trauma or during a procedure. Abnormal bleeding may not manifest until later in life.
Answer choice B: Factor IX deficiency (hemophilia B) and answer choice C: factor XI deficiency (hemophilia C) are far less common, making them incorrect.
Answer choice D: Immune thrombocytopenia is incorrect. Immune thrombocytopenia is a platelet disorder characterized by superficial bleeds such as petechiae, purpura, epistaxis, or mucous membrane bleeds.
Answer choice E: Thrombotic thrombocytopenic purpura, is incorrect. Thrombotic thrombocytopenic purpura is also a platelet disorder characterized by purpura, which are purple-colored patches that occur on the skin and in mucous membranes, including the lining of the mouth.
Key Learning Point
Hemophilia A is the most common hemophilia and is the result of clotting factor VIII deficiency. Remember that clotting factor deficiency (VIII, IX, or XI) matches with which hemophilia type (A, B, and C, respectively).
