doc179
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Found this qn in another forum:
A 5-year-old boy is being evaluated for recurrent epistaxis and other abnormal bleeding episodes, including excessive bleeding from the umbilical cord at birth. Laboratory studies reveal the following: decreased hemoglobin (with microcytic hypochromic red cell indices), normal platelet count, markedly prolonged prothrombin time (PT) and partial thromboplastin time (PTT), and unmeasurable thrombin time (TT). Platelet aggregation studies reveal a normal platelet response to ristocetin, but with other substances (including collagen, ADP, and epinephrine), this patient?s platelets exhibit a primary wave defect. Based on these findings, which of the following is the most likely diagnosis?
A. Afibrinogenemia
B. Bernard-Soulier syndrome
C. Glanzmann?s thrombasthenia
D. Gray platelet syndrome
E. Wiskott-Aldrich syndrome
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| doc179
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What is this primary wave defect?
I think it cannot be E platelet counts are normal.
It cannot be B since ristocetin test is normal.
In thrombasthenia, clot forms but does not retract normally. So not C.
So is it D or A?
Please help!
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| p53
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I think it's C. Glanzmann's thrombasthenia
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| doc179
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I know that in Glanzmann's GP 2b/3a is deficient with thrombocthenia..deficient contractile protien in the thrombocytes but there is no defect in the coagulant factors . In the Q PT and PTT is prolonged I dont understand this actually..could you pls explain and also tell me why and how you ruled out other choices..thank you very much
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| doc179
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I think the ans is A
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| nida
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The answer is C)
Bleeding due to defective platelet aggregation is exemplified by Glanzmann's thrombasthenia, which is also transmitted as an autosomal recessive trait. Thrombasthenic platelets fail to aggregate in response to adenosine diphosphate (ADP), collagen, epinephrine, or thrombin owing to deficiency or dysfunction of glycoprotein IIb-IIIa, a protein complex that participates in the formation of "bridges" between platelets by binding fibrinogen and vWF.
(Robbins)
Table from Harrison online
A. Platelet aggregation
1. Epinephrine: No observable response
2. ADP and thrombin: Shape change, but no aggregation
3. Collagen: Shape change followed by variable increase in light transmission most likely resulting from progressive adhesion to collagen fibers (pseudoaggregation)
4. Ristocetin: Normal initial slope of aggregation; at low doses, inhibition of second wave; at high doses, cyclical aggregation–disaggregation.
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| doc179
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thank you very much...but I dont understand why PT and PTT are prolonged...could you pls explain this to me...thanx
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| nida
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The main reason is IIb/IIIa bridges fibrinogen (affect PTT) and vWF (affect PT),
so both PT and PTT prolonged.
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| doc179
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hmm I could have never figured this out all by myself ...thank you nida.
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| robin082006
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this question is from Pretest series
Correct answer is A: Afibrinogenemia
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| doc179
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now I am really confused I had opted for A..I will look up in the pretest..
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| robin082006
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[left]206. The answer is a. (Cotran, p 637. Henry, pp 247, 710–713.) Platelet[/left] [left]aggregation refers to platelets binding to other platelets. One mechanism[/left] [left]for this involves fibrinogen, which can act as a molecular bridge between[/left] [left]adjacent platelets by binding to GpIIb and GpIIIa receptors on the surface[/left] [left]of platelets. Abnormalities of platelet aggregation (aggregation defects or[/left] [left]primary wave defects) include Glanzmann’s thrombasthenia and afibrinogenemia.[/left] [left]Patients with Glanzmann’s thrombasthenia have a deficiency of[/left] [left]GpIIb-IIIa and defective platelet aggregation. Patients with low or no fibrinogen[/left] [left]levels characteristically have prolonged PT, PTT, and TT values:[/left] [left]in fact, they are so prolonged they are unmeasurable.[/left]
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| doc179
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thank you very much robin082006....
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| doc179
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yes found the Q and answer in pretest...thank you robin
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| docsrinu
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very difficult q and excellent explanation.
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