Idiopathic Thrombocytopenic Purpura (ITP)

IDIOPATHIC THROMBOCYTOPENIC PURPURA (ITP)

ITP is a disease that affects people of all ages, but it is more com-mon among children and young women. There are two forms of ITP: acute and chronic. The acute form, which occurs predomi-nately in children, often appears 1 to 6 weeks after a viral illness. This form is self-limited; remission often occurs spontaneously within 6 months. Occasionally, corticosteroids are needed for a brief time. Chronic ITP is often diagnosed by exclusion of other causes of thrombocytopenia.

Pathophysiology

Although the precise cause remains unknown, viral infections sometimes precede ITP in children. Occasionally medications such as sulfa drugs can induce ITP. Other conditions, such as systemic lupus erythematosus (SLE) or pregnancy, can also induce ITP. Anti-platelet autoantibodies that bind to the patient’s platelets are found in the blood of patients with ITP. When the platelets are bound by the antibodies, the RES or tissue macrophage system ingests the platelets, destroying them. The body attempts to com-pensate for this destruction by increasing platelet production within the marrow.

Clinical Manifestations

Many patients have no symptoms, and the low platelet count (often less than 20,000/mm³, and less than 5000/mm³ is not un-common) is an incidental finding. Common physical manifes-tations are easy bruising, heavy menses, and petechiae on the extremities or trunk. Patients with simple bruising or petechiae (“dry purpura”) tend to have fewer complications from bleeding than those with bleeding from mucosal surfaces, such as the gastrointestinal tract (including the mouth) and pulmonary sys-tem (eg, hemoptysis), which is termed “wet purpura.” Patients with wet purpura have a greater risk for intracranial bleeding than do those with dry purpura. Despite low platelet counts, the platelets are young and very functional. They adhere to en-dothelial surfaces and to one another, so spontaneous bleeding does not always occur.

Assessment and Diagnostic Findings

Patients may have an isolated decrease in platelets (less than 20,000/mm³ is common), but they may also have an increase in megakaryocytes (platelet precursors) within the marrow, as de-tected on bone marrow aspirate.

Medical Management

The primary goal of treatment is a safe platelet count. Because the risk of bleeding typically does not increase until the platelet count is lower than 10,000/mm³, patients whose counts exceed 30,000 to 50,000/mm³ may be carefully observed without additional intervention. However, if the count is lower than 20,000/mm³, or if bleeding occurs, the goal is to improve the pa-tient’s platelet count, rather than to cure the disease. Treatment for ITP usually requires several approaches. If the patient is tak-ing a medication that is known to cause ITP (eg, quinine, sulfa-containing medications), that medication must be stopped immediately. The mainstay of short-term therapy is the use of immunosuppressive agents. The immunosuppressants block the binding receptors on macrophages so that the platelets are not destroyed. Prednisone is the agent typically used (at a dose of 1 mg/kg), and it is effective in about 75% of patients. Cyclophos-phamide (eg, Cytoxan) and azathioprine (Imuran) can also be used, and dexamethasone (eg, Decadron) may be effective. Platelet counts rise within a few days after institution of corti-costeroid therapy; this effect takes longer with azathioprine. Be-cause of the associated side effects, patients cannot take high doses of corticosteroids indefinitely. It is not unusual for the platelet count to drop once the corticosteroid dose is tapered. Some patients can be successfully maintained on low doses of prednisone (eg, 2.5 to 10 mg every other day).

Intravenous gamma globulin (IVIG) is also commonly used to treat ITP. It is effective in binding the receptors on the macrophages; however, high doses (1 g/kg for 2 days) are re-quired, and the drug is very expensive. Splenectomy is an alter-native treatment but results in a normal platelet count only 50% of the time; however, many patients can maintain a “safe” platelet count of more than 30,000/mm³ after removal of the spleen. Even those who do respond to splenectomy may have recurrences of severe thrombocytopenia months or years later. Patients who have splenectomy are permanently at risk for sepsis; these patients should receive Pneumovax, Haemophilus influenzae B, and meningococcal vaccines, preferably 2 to 3 weeks before the splenectomy is preferred. Pneumovax vaccine should be repeated at 5- to 10-year intervals.

Other options for management include use of the chemother-apy agent vincristine (Oncovin). Vincristine appears to work by blocking the receptors on the macrophages and therefore in-hibiting platelet destruction; it may also stimulate throm-bopoiesis. Some data support the efficacy of certain monoclonal antibodies (eg, rituximab) in increasing platelet counts, but more research is needed (Stasi, Pagano, Stipa, & Amadori, 2001; Saleh et al., 2000).

Another approach to the management of chronic ITP involves the use of anti-D (eg, WinRho) in patients who are Rh(D)-posi-tive. The actual mechanism of action is unknown. One theory is that the anti-D binds to the patient’s RBCs, which are in turn de-stroyed by the body’s macrophages. While the macrophages de-stroy the anti-D/RBC complex, they are not able to destroy platelets. Anti-D produces a transient decreased hematocrit and increased platelet count in many, but not all, patients with ITP. Anti-D appears to be most effective in children with ITP and least effective in patients who have undergone splenectomy.

Despite the extremely low platelet count, platelet transfusions are usually avoided. Transfusions tend to be ineffective because the patient’s anti-platelet antibodies bind with the transfused platelets, causing them to be destroyed. Platelet counts can actually drop after platelet transfusion. Occasionally, transfusion of platelets may protect against catastrophic bleeding in patients with severe wet purpura. Epsilon-aminocaproic acid (EACA; Amicar) may be use-ful for patients with significant mucosal bleeding refractory to other treatments.

Nursing Management

Nursing care for these patients should include an assessment of the patient’s life style to determine the risk of bleeding from activity. A careful medication history should also be obtained, including use of over-the-counter medications, herbs, and nutritional supple-ments. The nurse must be alert for sulfa-containing medications and medications that alter platelet function (eg, medications that contain aspirin or other NSAIDs). The nurse should assess for any history of recent viral illness and reports of headache or visual dis-turbances (which could be initial symptoms of intracranial bleed-ing). Patients who are admitted to the hospital with wet purpura and low platelet counts should have a neurologic assessment in-corporated into their routine vital sign measurements. No intra-muscular injections or rectal medications should be administered, and rectal temperature measurements should not be performed, because they can stimulate bleeding.

Patient teaching should address signs of exacerbation of disease (petechiae, ecchymoses); how to contact appropriate health care personnel; the name and type of medication inducing ITP (if appropriate); current medical treatment (medications, tapering schedule if relevant, side effects); and the frequency of monitoring the platelet count. Patients should be instructed to avoid all agents that interfere with platelet function. The patient should avoid con-stipation, the Valsalva maneuver (eg, straining at stool), and floss-ing of the teeth. Electric razors should be used for shaving, and soft-bristled toothbrushes should replace stiff-bristled ones. Pa-tients should also be counseled to refrain from vigorous sexual intercourse when the platelet count is less than 10,000/mm³. Pa-tients who are receiving chronic corticosteroids are at risk for complications including osteoporosis, proximal muscle wasting, cataract formation, and dental caries (see Chart 33-4). Bone min-eral density should be monitored, and these patients may benefit from calcium and vitamin D supplementation and bisphosphonate therapy to prevent significant bone disease.