WBR0254
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry, MainCategory::Genetics |
| Sub Category | SubCategory::Hematology |
| Prompt | [[Prompt::A 16 year old male with cystic acne presents to his dermatologist after noting several large bruises spread across his body. The patient denies any history of trauma and cannot recall any previous history of easy bruising. He has been maintained on isotretinoin and clindamycin for the past six months without incident. The mechanism of the most likely clotting abnormality in this patient is most similar to which of the following bleeding conditions?]] |
| Answer A | AnswerA::Factor V Leiden |
| Answer A Explanation | [[AnswerAExp::Factor V can be mutated to a prothrombotic isoform termed Factor V Leiden. This is the most common cause of hereditary prothrombotic syndrome. The Factor V Leiden mutation produces a gene product that cannot be degraded by protein C, resulting in increased Factor V levels. The vitamin K deficiency of this patient results in decreased coagulability by decreasing the levels of coagulation factors 2,7,9,,10 as well as protein C and S.]] |
| Answer B | AnswerB::Glanzman’s Thrombosthenia |
| Answer B Explanation | AnswerBExp::While Glanzman’s thrombosthenia may cause increased bleeding, it is an abnormality of platelet function and not the coagulation cascade (like vitamin K deficiency). |
| Answer C | AnswerC::Hemophilia A |
| Answer C Explanation | AnswerCExp::Hemophilia A is caused by a deficiency of Factor IX. This factor is also decreased in Vitamin K Deficiency. |
| Answer D | AnswerD::Thrombotic Thrombocytopenic Purpura |
| Answer D Explanation | AnswerDExp::Thrombotic Thrombocytopenic Purpura is primarily a disorder affecting platelet function. |
| Answer E | AnswerE::Protein C deficiency |
| Answer E Explanation | AnswerEExp::While Protein C is decreased by vitamin K deficiency, the main symptom of vitamin K deficiency is a decrease in coabulability. Pure protein C deficiency causes hyper coagulability. |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient in this vignette has Vitamin K deficiency secondary to depletion of Vitamin K producing gut bacteria with prolonged antibiotic use. Vitamin K is responsible for gamma hydroxylation of glutamic acid residues on several clotting factors. When vitamin K is deficient, the synthesis of these clotting factors is disturbed and the patient suffers increased bleeding.
The Vitamin K dependent clotting factors are: Factors 2,7,9,10, Protein C, and Protein S. Therefore, Vitamin K deficiency mimics hemophilia A (factor 9 deficiency). Vitamin K deficiency is NOT treated solely with Vitamin K supplementation. Because it takes the liver time to synthesize clotting factors even in the presence of adequate Vitamin K, Fresh Frozen Plasma (FFP) is infused. Similarly, Hemophilia A is a syndrome characterized by increased bleeding. Hemophilia A is also caused by deficiency of Factor IX. In both haemophilia A and B, spontaneous bleeding is common. On laboratory testing, these patients have a normal bleeding time, normal prothrombin time, normal thrombin time, but prolonged partial thromboplastin time. The most characteristic type of internal bleed is a joint bleed where blood enters into the joint spaces. Bleeding can be controlled with regular infusions of the deficient clotting factor, i.e. factor VIII in haemophilia A or factor IX in haemophilia B. Mann KG, Nesheim ME, Church WR, Haley P, Krishnaswamy S. Surface-dependent reactions of the vitamin K-dependent enzyme complexes. Blood. 1990;76(1):1-16.]] |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Vitamin K, WBRKeyword::Hemophilia, WBRKeyword::Haemophilia, WBRKeyword::Bruising, WBRKeyword::Bleed, WBRKeyword::Bleeding, WBRKeyword::Coagulation, WBRKeyword::Vitamin, WBRKeyword::Genetics, WBRKeyword::Blood, WBRKeyword::Hematology, WBRKeyword::Thrombosis |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |