Question

A 16-year-old boy presents with a marked hemarthrosis of his knee after tripping and striking it against the edge of a step. This has happened in the past. His activated partial thromboplastin time is prolonged and his prothrombin time and thrombin time are normal. What is the most likely diagnosis?

1) AFactor II deficiency
2) BHemophilia B
3) CVitamin K deficiency
4) DVon Willebrand disease

Answer 1

The most likely diagnosis for the boy with hemarthrosis, prolonged aPTT, and normal PT and TT is Hemophilia B, which involves a deficiency of factor IX and is inherited in an X-linked recessive manner.

Step-by-step explanation:

The most likely diagnosis for a 16-year-old boy with marked hemarthrosis of the knee, a history of similar episodes, prolonged activated partial thromboplastin time (aPTT), and normal prothrombin time (PT) and thrombin time (TT), would be Hemophilia B. This disorder is characterized by a deficiency in clotting factor IX, which is needed for blood to clot properly. Hemophilia B is inherited in an X-linked recessive pattern, affecting mainly males. Patients with this condition have a tendency to bleed from minor wounds and may experience spontaneous bleeding into joints, muscles, and other tissues.

Hemophilia A should also be considered in such cases as it is more common and involves a deficiency of factor VIII. However, given the specific laboratory results and the common presentation, Hemophilia B is the most likely diagnosis among the options provided. The other options, such as vitamin K deficiency or von Willebrand disease, tend to affect different components of the clotting cascade or present with additional laboratory abnormalities not seen in this case.