Wednesday, December 22, 2010

Clinical Case: A Child With Swollen Left Knee

Clinical Vignette: A 6-year-old boy was referred with swelling of his left knee. He had played football in his school playground 48 hours before and had not noticed any problems until the morning of referral. He had had no other problems. There was no family or personal history of significance. On examination, an otherwise well-looking boy had a red swollen knee which was warm and moderately painful to move. He was not systemically unwell and had a pyrexia of 37.3°C. Results of investigations were as follows:

Hb  11.8 g/dL
WBC 6.9 × 109/L
Platelets 405 × 109/L
Bleeding time normal
Prothrombin time 13 s (normal range 11–15)
Activated partial thromboplastin time 60 s (control 25–34)
Factor VIII level 123 per cent

What is the diagnosis?
    (a) Von Willebrand’s disease
    (b) Factor VIII deficiency
    (c) Factor V (Leiden) mutation
    (d) Factor IX deficiency
    (e) Protein C deficiency

Answer: (d)

A 6-year-old boy presents with a painful, red,swollen knee. There is no evidence of systemic infection but he has a prolonged APTT with normal factor VIII levels

Differential diagnosis
Well I cant stress it more but know these disease in the clinical vignette for your USMLE.
The clinical history suggests a differential diagnosis of haemarthrosis or septic arthritis. However,the prolonged APTT make this a haemarthrosis.
The normal bleeding time and platelet level make this a defect of the clotting cascade, and the APTT and prothrombin time put it in the intrinsic pathway. The most common defect, factor VIII deficiency or haemophilia A, is excluded; the answer is the next most likely, factor IX deficiency or haemophilia B. The lack of a family history is of no significance as one-third of patients carry new mutations.