Platelet disorders

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11.4 Platelet disorders

1 Abnormal bleeding can occur from disorders of total numbers of platelets or platelet function.

2 The normal platelet count is between 150 and 400 × 10⁹ L⁻¹.

3 Idiopathic thrombocytopenic purpura (ITP) is the commonest platelet disorder in childhood.

Introduction

The normal platelet count is between 150 and 400 × 10⁹ L^–1 and platelets usually exist within the circulation for 5–7 days. In normal haemostasis, blood loss is initially limited by the formation of a platelet plug and cross-linked fibrin at the site of injury. In platelet disorders this platelet plug is not formed or is ineffective, and abnormal bleeding occurs. Platelet abnormalities can be either quantitative or qualitative. Small petechial skin haemorrhages, less than 3 mm in diameter, are characteristic of platelet defects.

The commonest platelet disorder is thrombocytopenia (low platelet count). Significant thrombocytopenia has a characteristic bleeding profile of spontaneous bruising, petechiae, epistaxis and mucosal bleeding. Bleeding complications usually only occur at levels of less than 50 × 10⁹ L^–1, with spontaneous bleeding possible at levels below 10 × 10⁹ L^–1. As most platelet counts are performed by electronic particle counters, an inappropriately low platelet count can result from the spontaneous platelet clumping that can occur in EDTA collection tubes. This is confirmed by direct inspection of the peripheral blood smear for platelet clumping.

In qualitative disorders of platelet function the abnormal bleeding occurs despite a normal platelet count. Platelet dysfunction may occur in hepatic failure, chronic renal failure, myeloproliferative disorders, with some drugs (e.g. aspirin) and in rare inherited disorders of platelet function (Glanzmann, Portsmouth, Hermansky–Pudlak, May–Hegglin and Bernard–Soulier syndromes).

Thrombocytosis (elevated platelet count) is seen in inflammatory reactions including Kawasaki disease, patients with malignancy and polycythaemia rubra vera. Thrombocytosis of itself is rarely of clinical importance but platelet levels greater than 1000 × 10⁹ L^–1 can be associated with acute thrombosis or haemorrhage.

Idiopathic thrombocytopenic purpura

Introduction

Idiopathic thrombocytopenic purpura (ITP) is the commonest platelet disorder in children. It is an autoimmune disorder characterised by the development of platelet autoantibodies leading to decreased platelet survival. The incidence of ITP peaks in winter and spring due to the increased incidence of viral infections at those times. ITP in children is usually of the acute form, which lasts for less than 6 months, with a high rate of spontaneous resolution. ITP in children is most common between the ages of 2 and 6 years, but can occur in any age group. Up to 28% of children with ITP will develop a chronic form which lasts longer than 6 months.

Clinical presentation

ITP typically presents up to 3 weeks following a viral-type infection or vaccination. There is generally a short history of bruising, non-blanching rash (petechiae or purpura) or mucosal bleeding in an otherwise well child. The mucosal bleeding is usually from the gums or nose. Haematuria is also common. The petechial rash may appear in crops over several days. The physical examination is otherwise normal, with no signs of hepatosplenomegaly or lymphadenopathy.

Investigation

The blood count will demonstrate thrombocytopenia. Abnormally large and/or abnormally small platelets may be seen on the film. The blood count and film are otherwise usually normal. Anaemia may be present, dependent on the extent of previous haemorrhage. Eosinophilia may be noted, but is not consistent. Coagulation studies will be normal, bleeding time prolonged. There is no specific antiplatelet antibody test available for routine clinical use. Bone marrow aspiration is usually performed after 4 weeks if there is no evidence of remission, or earlier if the diagnosis is unclear.

Differential diagnosis

The diagnosis of ITP relies on the presence of laboratory-demonstrated thrombocytopenia, with a history, clinical examination and full blood count that do not suggest another cause. In the presence of a limp, hepatosplenomegaly or lymphadenopathy, consider the possibility of an underlying lymphoproliferative disorder. In infants with bruising, intentional injury must be excluded. In Wiskott–Aldrich syndrome eczema is present in the first year and the platelets are smaller than normal. The presence of other congenital abnormalities might be a clue to Fanconi’s anaemia. In older children, particularly those with a chronic course, a systemic autoimmune disorder such as lupus or antiphospholipid syndrome should be considered. In infants, exclude cytomegalovirus and consider immunoglobulins and T/B lymphocyte subsets to exclude immune disorders.

Management

Most children recover spontaneously within 6 to 8 weeks and have only cutaneous or mild bleeding. They require no specialist treatment and can be managed as ambulatory patients. Parents should be supported with good written advice on the condition and given a telephone contact name and number. Written advice should include information about avoiding contact sports, bangs to the head, aspirin and other drugs that interfere with platelet function. They should watch for bleeding and report to hospital if new episodes occur. In the initial stages the platelet count can be reviewed weekly but this can be extended to every 2 to 4 weeks once it is improving. School can be recommenced when platelets are greater than 20 × 10⁹ L^–1. By 6 months around 85% will have a normal platelet count. Patients with platelet counts greater than 150 × 10⁹ L^–1 can be discharged but warned that occasional relapses are seen and to re-present if symptoms recur.

Consider admission of patients with initial platelet counts below 20 × 10⁹ L^–1. Serious bleeding is rare in ITP, with intracranial haemorrhage occurring in ~1% of patients with platelet counts less than 20 × 10⁹ L^–1. All children with counts less than 10 × 10⁹ L^–1 during the course of the illness should be admitted. The decision to admit may be influenced by the social circumstances and parents’ coping ability.

Consider treatment if bleeding is severe. There are a number of established options aimed at increasing the platelet count but there is no specific therapy to treat the underlying disorder.

Current treatments

Asymptomatic children with acute ITP and platelet count <20 × 10⁹ L^–1 should be carefully observed. In the presence of purpura, significant mucosal membrane bleeding or other haemorrhage, intravenous immunoglobulin (IVIG) infusion is recommended and high-dose oral glucocorticoids can be considered with the involvement of a paediatric haematologist.

IVIG infusion will lead to a rapid platelet count rise, usually within 48 hours, lasting for 2–4 weeks. As a pooled blood product IVIG carries the risk of viral transmission and is expensive. A range of side effects have been reported.

High-dose oral steroids may also be considered, although IVIG has been demonstrated to promote a faster response to get platelet numbers above 50 × 10⁹ L^–1.

Anti-D is an effective alternative in Rh-positive children only, but the platelet increase is slower, taking 48–72 hours.

Splenectomy is reserved for life-threatening haemorrhage or children with significant bleeding who have failed to respond to medical treatment.Post-splenectomy patients have an increased risk of sepsis despite pneumococcal vaccination and antibiotic prophylaxis.

Medical emergencies

The risk of intracranial haemorrhage is less than 1% but persists as long as the platelet count is very low. Children with ITP and severe headache with neurological signs require urgent investigation with cranial computerised tomography scan and immediate treatment if indicated with IVIG and steroids. Life-threatening haemorrhage is the only instance where platelet transfusions should be used, as the antibodies in ITP target all platelets including donor transfusions. As a result the benefit of any transfusion is very short-lived. Emergency splenectomy may be used as a last resort.

Chronic ITP

Around 10–28% of children fail to remit within 6 months but spontaneous remission will occur in up to two-thirds of these patients in subsequent years. A chronic course is most often seen in older children, particularly adolescent girls. Some may have underlying conditions such as lupus. Most do not have significant bleeding problems or a need for regular treatment.

The Intercontinental Childhood ITP Registry was established in 1997 to prospectively investigate the clinical course, management and outcome of children with ITP. Since then a Splenectomy Register and a prospective database on both paediatric and adult patients with chronic ITP have also been set up. Information from these databases should provide the evidence base for the optimum treatment strategy for individual children with ITP in the future.

Acknowledgement

The contribution of Kieran Cunningham as author in the first edition is hereby acknowledged.

Further reading

Pediatric Blood Cancer, 47. 2006;S5:649-745.

The Intercontinental Cooperative ITP Study Group (ICIS). website: http://www.itpbasel.ch/Home.90.0.html

Greer J.P., Foerster J., Rodgers GM., et al, editors. Wintrobe’s Clinical Haematology, 12th ed., Baltimore: Lippincott Williams & Wilkins, 2008.

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Textbook of Paediatric Emergency Medicine