Idiopathic Thrombocytopenic Purpura
Thrombocytopenia that results from immunologic platelet destruction is known as idiopathic thrombocytopenic purpura (ITP). This form of thrombocytopenia may be acute (postviral thrombocytopenia) or chronic (Werlhof’s disease, purpura hemorrhagica, essential thrombocytopenia, or autoimmune thrombocytopenia). The acute form usually affects children between ages 2 and 6; the chronic form mainly affects adults younger than age 50, especially females between ages 20 and 40. The prognosis for the acute form is excellent: Nearly four out of five patients recover completely without specific treatment. The prognosis for the chronic form is good: Transient remissions lasting weeks or even years are common, especially among females.
Causes
ITP is an autoimmune disorder. Antibodies that reduce the life span of platelets have been found in nearly all patients. The spleen probably helps to remove platelets modified by the antibody. The acute form usually follows a viral infection, such as rubella and chickenpox, and can result from immunization with a live vaccine. The chronic form seldom follows infection and is often linked with other immunologic disorders such as systemic lupus erythematosus.
Human immunodeficiency virus (HIV) infection has become a common cause of ITP and should be considered in the differential diagnosis. ITP can be the initial symptom of HIV infection, a symptom indicating acquired immunodeficiency syndrome (AIDS), or a complication of AIDS. It’s also commonly a precursor to lymphoma.
Complications
As with other purpuric conditions, hemorrhage can severely complicate ITP. A major complication during the initial phase of the disease, cerebral hemorrhage is most likely to occur if the patient’s platelet count falls below 500/mm3. Hematomas on nerve or brain tissue may result in paralysis or extremity anesthesia. Bleeding into the diaphragm can result in pulmonary complications. Potentially fatal purpuric lesions may occur in vital organs, such as the brain, intestinal tract, and kidneys.
Assessment
The patient’s history usually reveals clinical features common to all forms of thrombocytopenia: epistaxis, oral bleeding, and the development of ecchymosis, easy bruising, purpura, and petechiae. A female patient may complain of menorrhagia. In the acute form, the sudden onset of bleeding usually follows a recent viral illness, although bleeding can occur up to 21 days after the virus strikes. In the chronic form, the onset of bleeding is insidious.
Inspection typically reveals petechiae or ecchymoses in the skin or bleeding into mucous membranes (GI, urinary, vaginal, or respiratory). Palpation may reveal splenomegaly.
The patient’s platelet count determines the type of abnormal bleeding he experiences.
For example, a platelet count between 30,000 and 50,000/mm3 causes bruising with minor trauma. A platelet count between 15,000 and 30,000/mm3 produces spontaneous bruising and petechiae, mostly on the arms and legs. A platelet count below 15,000/mm3triggers spontaneous bruising or, after minor trauma, mucosal bleeding, generalized purpura, epistaxis, hematuria, and GI or intracranial bleeding.
For example, a platelet count between 30,000 and 50,000/mm3 causes bruising with minor trauma. A platelet count between 15,000 and 30,000/mm3 produces spontaneous bruising and petechiae, mostly on the arms and legs. A platelet count below 15,000/mm3triggers spontaneous bruising or, after minor trauma, mucosal bleeding, generalized purpura, epistaxis, hematuria, and GI or intracranial bleeding.
Diagnostic tests
A platelet count less than 20,000/mm3 and prolonged bleeding time suggest ITP. Platelet size and morphologic appearance may be abnormal; anemia may be present if bleeding has occurred.
As in thrombocytopenia, bone marrow studies show an abundance of megakaryocytes (platelet precursors) and a shortened circulating platelet survival time (several hours or days rather than the usual 7 to 10 days).
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