Platelet Disorders

Platelet Disorders

von Willebrand’s disease

* the most common inherited coagulopathy caused by a defect in von Willebrand factor, which aids the binding of platelets to collagen
* chromosome 12, autosomal dominant
* Bleeding related to platelets (epistaxis, gingival, gums) with a normal platelet count;
* exacerbated by the use of aspirin
* it is a protective carrier for factor VIII; hence factor VIII may be low and hence aPTT may be elevated (50%)

Dx –

* low vWF (antigen) level;
* Ristocetin cofactor assay (or vWF activity) – detects vWF dysfunction; deficient ristocetin-induced platelet aggregation
* it means there is no response to ristocetin but this is corrected with the addition of normal plasma

* low factor VIIIc;
* prolonged BT

Scenario:
The combination of a petechial skin rash combined with a slightly elevated APTT and reduced factor VIII activity make Von Willebrand’s disease the most likely diagnosis, though hemophilia will be given in the answer choices

Tx –
DDAVP (desmopressin) if mild, and with vWF concentrate


Bernard-Soulier syndrome

  • autosomal recessive
  • disease of platelet adhesion which causes prolonged bleeding times in the presence of normal platelet counts.
  • These defective platelets cannot bind to subendothelial collagen properly because of a deficiency or dysfunction of the glycoprotein Ib-IX complex.
  • Dx
    • Clinically the patients have impaired hemeostasis and recurrent severe mucosal hemorrhage.
    • bleeding out of proportion to the degree of thrombocytopenia
    • mild thrombocytopenia, circulating “giant” platelets, severe platelet dysfunction; Hb may be low because of blood loss
    • platelets do not aggregate in response to ristocetin, but have a nornal aggregation in response to adenosine diphosphate (ADP), epinephrine and collagen
  • Tx
    • The only treatment for an acute episode is a transfusion of normal platelets.
    • Cryoprecipitate or vWF concentrate do not help

May–Hegglin anomaly (MHA)

  • May–Hegglin anomaly (MHA), also known as Dohle leukocyte inclusions with giant platelets and macrothrombocytopenia with leukocyte inclusions
  • autosomal dominant, MYH9 gene defect (22q12-13)
  • may found in association with Alport Syndrome
  • So, look for high frequency hearing loss (82%), proteinuria (40%), cataracts (25%), Hematuria (25%)

Glanzmann’s Thrombasthenia

autosomal recessive

platelet glycoprotein IIb/IIIa complex is either deficient or present but dysfunctional leading to defective platelet aggregation and subsequent bleeding

Dx

  • Platelet counts and other coagulation tests (PT, PTT) are normal
  • Prolonged BT
  • Primary platelet aggregation response to platelet agonists such as adenosine diphosphate, epinephrine, and collagen is decreased, while the response to ristocetin is normal

Tx

  • platelet transfusion in case of active bleeding

 

May-Hegglin anomaly is rare and not really tested in questions. Also, it is in fact primarily a morphology and quantitative platelet disorder but I put it as a side note to compare.

My way to remember:

  1. May-Hegglin is Dominant because of Dohle and Giant platelets; remember also Alport is (x-lined) dominant
  2. Bernard-Soulier has 2 names ADHERED (adhesion problem); so it becomes Giant and do not listen to Ristocetin
  3. Glanzmann has “G” for AGGreGation and aGree to ristocetin while response to others are decreased

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s