Platelet defects
Defects in either the number or the function of platelets may produce easy bruising, epistaxis and intestinal bleeding. Purpura is usually seen only when there is a fall in circulating platelets to around 10- 20 x 109/litre from the normal of 200-300 x 109/litre. Bleeding may occur at a level of up to 50 x 109/litre if there has been major surgery or extensive trauma.
There is usually a history of spontaneous bruising and bleeding, especially recurrent bilateral nose bleeds, mucous membrane bleeding in the mouth, persistent menorrhagia and intestinal bleeds. It is important to ask about recent drug therapy. Careful examination is required to identify a basic disease process such as infection, malignancy, liver disease or a connective tissue disorder. The age of the purpuric lesions may give a clue to the duration of the disease. Evidence of splenic enlargement should be sought. Investigations include TBC, platelet count, coagulation screen, bone marrow aspirate and bleeding time.
Idiopatic trombocytopenic purpura (ITP)
ITP is an autoimmune disorder characterized by the accelerated removal of platelets coated with antibody by cells of the reticulo-endothelial system. These antibodies may be found in lymphoproliferative disorders or after infections; rarely, they may be associated with drug therapy. The likelihood of haemorrhage is related to the degree of thrombocytopenia or interference with normal function. Clinically, ITP can be classified as acute or chronic.
In acute ITP purpura, bruises and bleeding appear abruptly, usually in children or young adults.
There is often a history of an upper respiratory tract infection in the preceding 2 weeks. Occasionally, there may have been an obvious viral disease such as measles, mumps or infectious mononucleosis. The blood film is usually normal, but may show some atypical lymphocytes. The platelet count is significantly reduced and some platelets may be larger than normal. Bone marrow examination shows an increase in megakaryocytes.