Differential Diagnosis and Prognosis of Chronic IT
Differential diagnosis
The diagnosis of chronic ITP is one of exclusion. Other causes must be ruled out by careful attention to the patient's history and physical examination and by performing indicated tests. A complete blood count is always needed and in many cases a bone marrow examination is recommended. Other tests may be needed, depending on the clinical presentation.
The disorders most commonly confused with chronic ITP are as follows:
- Drugs. Certain drugs may cause low platelet counts, often due to drug-dependent antiplatelet antibodies. The drugs that are most often involved are quinine, quinidine, sulfa, sulfa-like drugs, chlorothiazide, chloroquine, rifampcin, gold salts and heparin. In recent years, it has become apparent that platelet GPIIb/IIIa inhibitors that are used in the treatment of the acute coronary syndrome or in the management of angioplasty or coronary artery surgery (abciximab, eptifibatide and tirofiban) can cause platelet destruction and mimic ITP. However, many other drugs have caused thrombocytopenia in occasional patients. If a patient with thrombocytopenia is taking a potentially causitive drug, it should be stopped and the platelet count observed. If a drug is the cause, the platelet count will become normal within 2-3 weeks, although there are occasional exceptions (e.g., thrombocytopenia due to gold therapy in patients with rheumatoid arthritis).
- Immune thrombocytopenia associated with other diseases. Immune thrombocytopenia may be associated with a variety of diseases including: collagen vascular disease (such as systemic lupus erythematosus), lymphoproliferative disorders (such as chronic lymphocytic leukemia or non-Hodgkin's lymphoma), and infections (particularly viral infections such as HIV, cytomegalovirus, hepatitis and mononucleosis). These disorders can be ruled out by careful examination and the appropriate laboratory studies.
- Disorders associated with decreased platelet production. A variety of diseases such as aplastic anemia, acute leukemia, myelodysplasia, etc. can cause thrombocytopenia. These can be easily ruled out by evaluation of the blood count and bone marrow.
Clinical course and prognosis
In some patients, the platelet count recovers spontaneously, usually within the first few weeks. These patients may have another cause of thrombocytopenia such as a viral illness. Other chronic ITP patients (about 5-10%) have stable disease, with a platelet count of 30-100,000, which may persist for months to years and rarely requires treatment. Of patients who need treatment (platelet count consistently less than 25-30,000), approximately 75% are cured of their disease with either corticosteroids (cortisone) or by removal of their spleen (splenectomy). Most of the remaining patients can be controlled and sometimes cured of their disease with other forms of treatment. The mortality rate from chronic ITP is disputed but is probably between 1-4%.
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