Hemorrhagic diathesis - features and classification. Thrombocytopenia - classification. Autoimmune thrombocytopenia.
Hemorrhagic diathesis = a pathology that makes an individual unusually susceptible to bleeding mostly due to hypocoagulability, caused by a coagulopathy.
First let's think about an approach to bleeding. Haemostasis is the body mechanism to maintain the balance between bleeding and clotting, it has three distinct processes:
- Vessel wall .tissue factor activation
- Platelet plug formation
- Activation of the coagulation cascade
Defects in any of these will result in abnormal clotting or coagulation, these can be congenital or acquired
Use link to access chart of all bleeding disorders:
https://app.lucidchart.com/publicSegments/view/0b26729d-9e48-48a6-a98d-14739793dc6e/image.jpeg
The main methods and types of bleeding disorders are summarized here:
- Bleeding disorders
- Vessel wall disorders
- Congenital
- Hereditary hemorrhagic telangiectasia
- ehlers-Danlos
- Acquired
- Scurvy
- Vasculitis
- Platelet disorders
- Platelet dysfunction
- Congenital
- Bernard-Soulier
- Acquired
- Drugs (aspirin)
- Myeloproliferative disorders
- Renal/Liver failure
- Thrombocytopenia
- Reduced production
- BM failure
- Drug induced
- Myelodysplastic disorders
- Increased production
- Idiopathic thrombocytopenic purpura
- Heparin induced thrombocytopenia
- DIC
- Coagulation disorders
- Congenital
- Haemophiliacs
- Von Willebrand
- Factor VII, X, XIII deficiency
- Acquired
- Vitamin K def
- Renal, liver failure
- DIC
The above should make it clear there is a distinction between clotting disorders (where thrombocytes are required to form a blood clot) and coagulation disorders (where coagulation proteins form part of a coagulation cascade). These differences are also played out in clinical practice. Clotting disorders generally manifest within the skin or mucosal membranes as bleeding, bruising or purpura and occur spontaneously, while coagulation disorders tend to involve joints (haemarthrosis) or muscles and occur within hours to days.
We can perform tests to help distinguish if the cause of bleeding is a coagulopathy or a clotting disorder
- Platelet count - assess platelets and thrombocytopenia (clotting)
- Bleeding time - assess platelets and platelet dysfunction (eg von wilebrands, clotting)
- Activated partial thromboplastin time (APTT) - assess intrinsic pathway (coagulation)
- Monitor heparin therapy, haemophilia, DIC
- Prothrombin time - assess extrinsic pathway (coagulation)
- Liver disease, monitor warfarin therapy, DIC
- Fibrinogen levels - final common pathway is assessed (coagulation)
Image: “Coagulation Cascade with Tests” by Otocast, CC BY-SA 4.0, via Wikimedia Commons.
Thrombocytopenia
This is defined as reduced platelet count below 150x10*9/L, although spontaneous severe bleeding is unusual with counts above 20x10*9/L. There are a large number of causes of thrombocytopenia, some of them are listed below:
- Reduced platelet production
- Bone marrow failure
- Aplastic anemia, megaloblastic anemia, infiltration secondary to malignancy, cytotoxic drug, alcohol
- Inherited thrombocytopathies
- Bernard-Souilier syndrome, Alport syndrome, Wiskott syndrome
- Increased platelet consumption
- Immune
- Immune thrombocytopenic purpura (ITP)
- Heparin-induced thrombocytopenia (HIT)
- Non-immune