Differential Diagnosis for the 8-month-old Boy with Bruising
- Single most likely diagnosis:
- Hemophilia A (Factor VIII deficiency): The patient's symptoms, such as bruising and a swollen, tender knee without erythema or warmth, are consistent with a bleeding disorder. The prolonged partial thromboplastin time (PTT) with a normal prothrombin time (PT) and normal platelet count points towards a deficiency in the intrinsic coagulation pathway, which is characteristic of Hemophilia A.
- Other Likely diagnoses:
- Hemophilia B (Factor IX deficiency): Similar to Hemophilia A, Hemophilia B would present with prolonged PTT and normal PT. However, the specific factor deficiency would need to be identified through further testing.
- Vitamin K deficiency: Although less likely given the age and presentation, Vitamin K deficiency could lead to bleeding tendencies due to its role in the production of clotting factors. However, it would typically affect both PT and PTT.
- Do Not Miss diagnoses:
- Child abuse: It is crucial to consider non-accidental injury, especially with unexplained bruising. However, the pattern of bruising and the child's developmental stage (learning to crawl and stand) make accidental trauma more plausible in this scenario.
- Severe bleeding disorders (e.g., Factor X deficiency, Factor XIII deficiency): These are less common but would have significant implications for the patient's health. Factor X deficiency would affect both PT and PTT, and Factor XIII deficiency might not be detected through standard coagulation tests.
- Rare diagnoses:
- Factor VII deficiency: This would primarily affect the PT, which is not significantly prolonged in this patient.
- Abnormal platelet function: Given the normal platelet count and the specific pattern of coagulation test abnormalities, this is less likely to be the primary cause of the patient's symptoms.
- Vitamin K-dependent clotting factor deficiencies other than Factor VIII or IX: These would be rare and typically present with abnormalities in both PT and PTT.