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Idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura is the condition of having a low platelet count (thrombocytopenia) of no known cause (idiopathic). As most causes appear to be related to antibodies against platelets, it is also known as immune thrombocytopenic purpura. Although most cases are asymptomatic, very low platelet counts can lead to a bleeding diathesis and purpura. more...

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Signs and symptoms

ITP occurs most often in women over 40 years of age. It may be acute, lasting for 6 months or less, or chronic, lasting for over a year. The acute type is more often seen in children and will cure itself in more than 80% of cases. The chronic type is more commonly seen in adults and it tends to get worse as the disease progresses.

Occasionally, ITP patients suffer from bruising, nosebleeds, and bleeding gums; this is the characteristic pattern of bleeding in platelet disorders. Bleeding normally does not occur unless the platelet count is very low (below about 10,000 per mm³, compared to a normal range of 150,000–400,000 per mm³).

Subarachnoid and intracerebral hemorrhage are very serious possible complications of this disease. Fortunately, these are rare in patients who are being treated.

Pathogenesis

In many cases, the cause is not actually idiopathic but autoimmune, with antibodies against platelets being detected in approximately 80% of patients. Most often these antibodies are against platelet membrane glycoproteins IIb-IIIa or Ib-IX, and are of the IgG type. The coating of platelets with IgG renders them susceptible to opsonization and phagocytosis by splenic macrophages.

The IgG autoantibodies are also thought to damage megakaryocytes, the precursor cells to platelets, but this is thought to contribute only slightly to the decrease in platelet numbers.

Diagnosis

When measuring the platelet count, one has to bear in mind that the "normal values" for laboratory measures are all statistical. They are defined by the upper and lower 2.5th percentile. It is therefore possible to be completely healthy but to have a decreased platelet count. There is, however, a higher chance of pathology.

The diagnosis of ITP is a clinical one and is a diagnosis of exclusion. Low platelet count can be a feature of a large number of diseases and, when serious, warrants investigation by a hematologist. Secondary causes include leukemia, medications (e.g. quinine), lupus erythematosus and some other autoimmune disorders, cirrhosis (leading to thrombocytopenia from hypersplenism), HIV, congenital causes, and antiphospholipid syndrome. A bone marrow examination may be performed on patients over the age of 60 and people who do not respond to treatment, or when the diagnosis is in doubt.

Despite the destruction of platelets by splenic macrophages, the spleen is normally not enlarged. In fact, an enlarged spleen should lead a clinician to investigate other possible causes for the thrombocytopenia.

Accelerated formation of platelets results in the presence of abnormally large platelets which are seen in a peripheral blood smear. Overall bleeding time is prolonged in these patients, but prothrombin time (PT) and partial thromboplastin time (PTT) are normal (because the problem is with the platelets, not with the coagulation cascade).

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Splenectomy for idiopathic thrombocytopenic purpura - Tips from Other Journals
From American Family Physician, 4/1/03 by Anne D. Walling

In idiopathic thrombocytopenic purpura (ITP), the destruction of platelets by antiplatelet autoantibodies results in platelet phagocytosis by the spleen and reticuloendothelial system. The consequent risk of fatal bleeding in adults ranges from 0.4 percent to 13 percent per year, depending on patient age. The usual first-line treatment is corticosteroids, but because the spleen is the principal site of autoantibody production and platelet destruction, splenectomy is an effective second-line treatment. Gadenstatter and colleagues studied the role of splenectomy in the treatment of patients with ITP.

The study included 92 patients with ITP who presented to the hematology and oncology department of an Austrian university between 1991 and 2000. The median age of the 33 men and 59 women was 49 years (range: 15 to 93 years). All patients had laboratory-confirmed thrombocytopenia, and most had hemorrhagic symptoms with no plausible explanation except ITP. All patients initially were treated medically. Seventy-eight patients (85 percent) received glucocorticoid therapy alone. A combination of glucocorticoid and immunoglobulin treatment was used in nine patients (10 percent), and the remaining five patients (5 percent) had pulsed high-dose dexamethasone, immunoglobulin, or vinblastine therapy alone. Splenectomy performed by midline laparotomy was used when patients did not respond well to medical treatment, had severe bleeding, or developed complications from medical treatment.

The 38 patients (41 percent) who underwent splenectomy had a median interval of seven months of medical therapy (range: two to 13 months). Follow-up was completed in 91 patients (99 percent) after a median of 64 months (range: 46 to 117 months).

During medical therapy, side effects were documented in 32 patients (35 percent). The most common adverse effects involved cutaneous effects on the skin, but Cushingoid changes, gastrointestinal upset, myopathy, weight gain, hypertension, and osteoporosis were also common. Only two patients (5 percent) had complications resulting from surgical treatment. Complete remission (normal platelet count and no further therapy required) was achieved in 15 patients (16 percent) who received medical therapy and 33 patients (87 percent) who had splenectomy. Partial remission (nearly normal counts and no therapy required) was documented in 12 patients (13 percent) who were treated medically and two patients (5 percent) who were treated surgically. Overall, 64 patients (70 percent) failed to respond to medical therapy, and three patients (8 percent) failed to respond to splenectomy. In a stepwise logistic multivariate analysis, only patient age and splenectomy correlated with complete or partial remission.

The authors conclude that splenectomy is an effective and safe treatment of ITP, especially in younger patients, and exposes patients to fewer potential treatment-related adverse effects. They believe that laparoscopic splenectomy offers additional benefits but that a careful search must be made for accessory spleens that may be present in up to 20 percent of cases.

EDITOR'S NOTE: If the therapeutic pendulum swings back to splenectomy as the preferred treatment for a substantial proportion of patients with ITP, family physicians will become these patients' "safety net" for remembering their vulnerability to other autoimmune diseases and to severe infections, particularly those caused by Pneumococcus. Following splenectomy for ITP, patients need lifelong special attention to disease prevention and early detection of potential problems. I am surprised constantly by how many patients are found to have significant medical problems that they have forgotten about or that have not been recorded in their medical chart. Nothing beats asking the patient, but it is not unusual for them to recall surgeries only when asked about obvious scars. What will we do when laparoscopic surgeries become even more common and our eyesight fades?--A.D.W.

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