This patient does not have an infection of the legs. The patient correctly noticed that the area around the traumatized skin became erythematous, but careful inspection reveals no signs of infection. There is no tenderness, induration, edema, or discharge associated. The patient is afebrile, and has no lymphadenopathy. A complete cell count and peripheral smear was done, and demonstrated only thrombocytopenia. Coagulation studies and renal function were normal. The patient's platelet count was 3,200 /μL. She was admitted to the hospital, and hematology was consulted. She was started on prednisone, and discharged once her platelet count was above 30,000 /μL.
Idiopathic (immune) thrombocytopenic purpura (ITP) is presumed to be an autoimmune disorder characterized by thrombocytopenia and mucocutaneous bleeding. In the majority of patients, auto-antibodies are produced that react with a surface protein on the platelet, such as the IIB/IIIA glycoprotein. These antibody-coated platelets are then recognized by antigen-presenting cells (macrophages and dendritic cells) within the spleen and liver, and are internalized and degraded. Through interactions with the antigen-presenting cell, T cells and B cells, more antibodies toward that surface protein are produced as well as other novel antibodies directed at other platelet surface proteins, significantly amplifying the production of antibodies directed against platelets and platelet destruction.
ITP inflicts children and adults, but the presentation and course of disease is quite different. In children, patients usually present with the sudden development of petechiae and purpura days to weeks after an infectious illness. Both boys and girls are equally affected. Resolution of the disease occurs in the majority of patients with or without treatment. In adults, however, the presentation is often more insidious, with more women than men affected. Patients not uncommonly relapse despite treatment. ITP may be primary or secondary to an underlying disorder such as systemic lupus erythematosus, lymphoproliferative disorders or immunodeficiency states, or may be drug-induced (e.g. heparin, quinidine, sulfonamides).
The diagnosis of primary ITP is one of exclusion. Besides excluding causes of secondary ITP as described above, other causes of thrombocytopenia must be ruled out. These include but are not limited to thrombotic thrombocytopenia purpura/hemolytic uremic syndrome (TTP/HUS) and disseminated intravascular coagulation (DIC). Patients with ITP will have a normal CBC except for the presence of thrombocytopenia and normal PT/ PTT. Renal function is not impaired, and the peripheral smear is normal except for decreased number of circulating platelets. In contrast to ITP, TTP will have thrombocytopenia and anemia. Renal function is usually impaired, and the peripheral smear will have schistocytes. Patients with DIC will not only have signs of a microangiopathic hemolytic anemia, but will also have prolonged PT and PTT along with low fibrinogen levels and increased fibrin degradation products.
Clinically, patients typically present to the ED with signs of mucocutaneous bleeding. Patients will complain of easy bruising and the presence of symmetrical dependent petechiae and purpura. These are nonpalpable and asymptomatic. This is in contrast with patients who present with vasculitic purpura which are palpable and often symptomatic where patients may complain of prodromal itching or burning. Vasculitic purpura does not tend to be dependently distributed. Patients with ITP may present with epistaxis, gingival bleeding or menorrhagia. Gastrointestinal bleeding, hematuria, and intracranial hemorrhage are rare and are typically seen in older patients with severe (<10,000 /μL) thrombocytopenia. Patients otherwise are well with no other signs of systemic illness, the presence of which such as fevers, weight loss, or joint pains should begin an investigation into an underlying disease that may cause secondary ITP.
Patients will have a normal CBC except for thrombocytopenia, a normal peripheral smear, and PT/PTT. There are limited data correlating clinical presentation with platelet count, most of which are derived from patients who have thrombocytopenia secondary to chemotherapy-induced marrow suppression. Unlike patients with chemo-induced thrombocytopenia, patients with ITP actually tend to have increased production of platelets and therefore are less symptomatic at similar platelet counts. In fact most patients who present to the ED will have platelet counts less than 10,000 /μL.
In general, treatment is not necessary for platelet counts greater than 30,000-50,000/μL. Treatment is usually begun once the platelet count drops to <30,000 μL. In adults, treatment begins with prednisone at a dose of 1-1.5 mg/kg/d. Anti-D immune globulin can be considered in Rh-positive patients instead of prednisone, although it is more expensive. If a patient presents with severe bleeding (intracranial hemorrhage, gastrointestinal bleeding) or is in need of emergency surgery, then intravenous methylprednisolone at a dose of 30 mg/kg/day (max 1 gm/day) along with intravenous immune globulin (1 gm/kg/d) should be administered. Platelets can be transfused, and if required, should be given in a dose two to three times the usual amount infused. Other treatments that can be considered include vincristine, splenectomy, and plasmapheresis.
Treatment in children is a bit more controversial, and may include observation, oral prednisone at the same or higher doses, intravenous immune globulin, and anti-D immune globulin. Significant relapses in adults are generally treated with splenectomy. In children, splenectomy is deferred as long as possible for fear of development of bacterial sepsis. It goes without saying that hematology should be consulted for all cases of ITP.