Platelets

Question 1

What is the normal role of platelets?

Answer 1

The main function of platelets is contribute to haemostasis aka to stop bleeding.

Firstly they adhere to the area of the interrupted endothelium.

Secondly they become activated changing shape and switching on receptors which send out chemical signals.

Thirdly they aggregate and stick together to form a platelet plug.

Platelets work alongside the coagulation cascade.

As a general rule of thumb platelets are more important for clotting in the arterial system and coagulation cascade is more important in the venous system.

Question 2

Discuss how platelets can contribute to the pathophysiology of thromboembolic events?

Answer 2

Platelets aggregate on ruptured aterosclerotic plaques this can further occlude a vessel and lead to ischaemia.

Secondly this thrombus may become detached and occlude an aa further along in the arterial system aka a thromboembolic event (CVD)

Question 3

Describe the mechanism of action of aspirin and its role in cardiovascular disease prevention?

Answer 3

Reduce the risk of thrombus formation and therefore reduces the risk of IHD, ACS and CVD.

Endothelial COX produces prostacylin and Platelet COX produces thromboxane.

Prostacylin inhibits platelet activation. Thromboxane stimulates activation of new platelets and platelet aggregation.

Aspirin favours prostacyclin production over thromboxane as it irreversibly inhibits both endothelial and platelet cyclo-oxygenase (COX).

Endothelial cell are nucleated and therefore can regenerate COX, platelets lack nuclei and therefore cannot.

Question 4

What are the clinical features of immune thrombocytopaenia?

Answer 4

Often presents with petechiae or purpura. May cause epistaxis or mucosal bleeding. In women may have menorrhagia.

Severe bleeding is rare.

Question 5

How should suspected ITP be investigated?

Answer 5

FBC and Blood film

Any atypical features such as:

• anaemia
• neutropenia
• hepatosplenomegaly
• marked lymphadenopathy

Should raise concern about a diagnosis of leukaemia, SLE and aplastic anaemia.

Question 6

How is ITP treated?

Answer 6

Usually self limiting and children usually recover in 6-8 weeks. In adults can often take longer.

Note ~20% take a chronic course lasting >6months (screen for SLE).

If there is any major bleeding or recurrent minor bleeding then treatment should be used.

Oral Prednisolone
IV anti D/ IV Ig

Platelet transfusion should be reserved for life threatening bleeds, lower threshold in adults as children can compensate more.