von Willebrand disease
Characterized by deficient levels of von Willebrand factor, which is responsible for platelet adhesion and acts as a binding protein for coagulation factor VIII.
Recall that von Willebrand factor is crucial in the early stages of
hemostasis, in which it acts as a bridge between circulating platelets and exposed subendothelial collagen; after their activation, von Willebrand factor bridges adjacent platelets.
von Willebrand disease is inherited as a genetic mutation, with three types:
Type 1 is the most common, and least severe; it is characterized by decreases in von Willebrand factor and coagulation factor VIII levels.
Type 2 is intermediate, and comprises several subtypes that vary in severity.
Type 3 is rare, but severe, and is characterized by nearly absent von Willebrand factor and factor VIII.
Be aware that von Willebrand disease can also be acquired, though this is rare.
Treatment includes desmopressin (ex: DDAVP), which induces release of von Willebrand factor and Factor VIII from the endothelium, and/or von Willebrand factor replacement therapy.
Thrombocytopenia
Characterized by platelet counts below 150 thousand per microliter of blood; normal platelet count is between 150-450 thousand per microliter of blood.
The causes of thrombocytopenia include:
Decreased platelet production in the bone marrow
Increased sequestration (particularly in the spleen)
Increased platelet destruction
Severity and treatment for thrombocytopenia depends on its causes.
A notable characteristic of mild to severe thrombocytopenia is the appearance of
petechiae, which are small reddish purple spots caused by blood leakage from capillaries. Recall that thousands of small nicks occur in the walls of the blood vessels each day; without sufficient platelet populations and plug formation, bleeding ensues.
