rare, typically adult females

Pathogenesis

• abnormally large and sticky multimers of von Willebrand's factor cause platelets to clump within vessels causing thrombocytopenia, bleeding under the skin and other systemic issues
• in TTP there is a deficiency of ADAMTS13 (a metalloprotease enzyme) which normally inactivates vWF and reduced platelet adhesion to vessel walls and clot formation. This deficiency leads to vWF overactivity and clot formation in small vessels using up platelets
• Deficiency in the ADAMTS13 protein can be due to an inherited genetic mutation or due to autoimmune disease where antibodies are created against the protein.

Causes

• post-infection e.g. urinary, gastrointestinal
• pregnancy
• drugs: ciclosporin, oral contraceptive pill, penicillin, clopidogrel, aciclovir
• tumours
• SLE
• HIV

The pentad to remember:

• Fever
• Microangiopathic haemolytic anaemia (MAHA)
• Thrombocytopaenic purpura
• CNS involvement: headache, confusion, seizures
• AKI