Thrombocytopenia

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Chapter 44 THROMBOCYTOPENIA

Theodore X. O’Connell

General Discussion

Normal platelet counts in children and term infants are 150,000 to 450,000/μL of blood. Normal platelet counts in preterm infants are in this same range but tend to average on the lower end of normal. Thrombocytopenia is defined as a platelet count of less than 150,000/μL of blood.

Idiopathic (immune) thrombocytopenic purpura (ITP) is the most common cause of thrombocytopenia in childhood and usually occurs in children between the ages of 2 and 4 years. In about 90% of children with ITP, the disease is an acute, self-limited process that usually resolves within 6 months. Chronic ITP is more common in children older than 10 years and in those younger than 1 year of age. In ITP, the complete blood count (CBC) will show an isolated thrombocytopenia with normal white (WBC) and red blood cell (RBC) counts. Examination of the peripheral smear is important to evaluate platelet size, WBC differential and morphology, RBC morphology, and to rule out the presence of microangiopathic changes such as schistocytes, which might suggest another diagnosis. If the history, physical examination, CBC, and peripheral smear are normal except for thrombocytopenia, a bone marrow biopsy may be deferred.

Neonatal thrombocytopenia is relatively common, occurring in 2% to 3% of healthy term infants and 20% to 30% of all sick neonates. In general, the thrombocytopenia seen in a sick infant is likely related to the primary disease process and resolves as the primary process improves.

Neonatal alloimmune thrombocytopenia occurs in 1 in 1000 births. The typical presentation is that of a full-term infant who is otherwise healthy, born after an uncomplicated pregnancy and delivery, and found to have petechiae or bruising on examination and confirmed to have a significant degree of thrombocytopenia. The thrombocytopenia is caused by transplacental passage of maternal alloantibodies directed against fetal platelet antigens inherited from the father but absent on maternal platelets. This process is the platelet equivalent of Rh-hemolytic disease of the newborn. In contrast to Rh-hemolytic disease of the newborn, neonatal alloimmune thrombocytopenia often develops in the first pregnancy of an at-risk couple.

The thrombocytopenia seen in autoimmune thrombocytopenia is less severe than in alloimmune thrombocytopenia, with only 10% to 15% of patients having a neonatal platelet count less than 50,000/μL. As such, autoimmune thrombocytopenia is associated with a lower bleeding rate. The history will reveal a low maternal platelet count, maternal ITP, or possibly maternal systemic lupus erythematosus (SLE) or hypothyroidism. All neonates of mothers with autoimmune disease should be considered for cord blood platelet count at birth and again at 24 hours to evaluate for thrombocytopenia. In affected children, spontaneous recovery of the platelet count usually occurs within 3 weeks after birth.

If the history and physical examination are not suggestive of thrombocytopenia, pseudothrombocytopenia or “artifactual” thrombocytopenia should be considered. The platelet count can be repeated using a citrated tube to assess the count in the absence of platelet clumping.

Medications Associated with Thrombocytopenia

• Alkylating agents

• Antiarrhythmic drugs

• Anticonvulsants

• Antimetabolites

• Chlorothiazide diuretics

• Cimetidine

• Estrogens

• H2 antagonists

• Heparin

• Nitrofurantoin

• Nonsteroidal antiinflammatory drugs (NSAIDs)

• Penicillin

• Quinidine

• Sulfonamides

• Ticlopidine

• Valproic acid

Causes of Thrombocytopenia

Neonatal

Alloimmune thrombocytopenia

Asphyxia

Congenital and inherited causes

• Amegakarocytic thrombocytopenia
• Autosomal dominant thrombocytopenia
• Bernard-Soulier syndrome
• Chediak-Higashi syndrome
• Congenital leukemia
• Fanconi’s anemia
• Fechtner syndrome
• Kasabach-Merritt syndrome
• May-Hegglin anomaly
• Montreal syndrome
• Quebec platelet disorder
• Sebastian syndrome
• Thrombocytopenia absent radius (TAR) syndrome
• Triploidy
• Trisomy 13
• Trisomy 18
• Trisomy 21
• Wiskott-Aldrich syndrome
• X-linked thrombocytopenia

Congenital infection

• Cytomegalovirus (CMV)
• Human immunodeficiency virus (HIV)
• Rubella
• Toxoplasma spp.

Disseminated intravascular coagulation (DIC)

Maternal idiopathic (immune) thrombocytopenia purpura

Metabolic disease

• Methylmalonic acidemia
• Proprionic acidemia

Necrotizing enterocolitis

Neonatal cold injury

Perinatal infection

• Escherichia coli
• Guillain-Barré syndrome
• Haemophilus influenzae

Placental insufficiency

Pregnancy-induced hypertension

Respiratory distress syndrome (RDS)

Rh hemolytic disease (severe)

Sepsis

Thrombosis of aortic or renal vein

Childhood

Aplastic anemia

Autoimmune disease

• Juvenile rheumatoid arthritis (RA)
• SLE

Bone marrow infiltration

• Granulomatous diseases
• Histiocytosis
• Leukemia
• Myelofibrosis
• Storage disorders

Disseminated intravascular coagulation

Drug induced thrombocytopenia

Fanconi anemia

Hemangioma

Hemolytic uremic syndrome

ITP

Immunodeficiencies

May-Hegglin anomaly

Thrombotic thrombocytopenia purpura

Type 2 von Willebrand disease

Key Historical Features

Onset and duration of bruising or bleeding

Location of bleeding

Antecedent viral infection

Fever

Weight loss

Bone pain

Joint pain

Abdominal pain

Blood in stools

Hematuria

Menometrorrhagia

Epistaxis

Medical history

Birth history

Maternal history if thrombocytopenia has neonatal onset

Past surgical history

Medications

Family history of bleeding disorder

Key Physical Findings

Vital signs, noting fever or hypertension

Growth parameters and comparison with previous measurements

General evaluation of well-being

Complete skin examination for purpura, pallor, rash, jaundice café-au-lait spots, or telangiectasias

Evaluation for lymphadenopathy

Abdominal examination for tenderness or hepatosplenomegaly

Genitourinary examination for scrotal edema

Extremity examination for edema, palmar erythema, or evidence of hemarthrosis

Suggested Work-up

CBC with differential To measure the platelet count and evaluate the other blood cell lines
Peripheral smear To evaluate platelet size, WBC differential and morphology RBC morphology, and to rule out the presence of microangiopathic changes such as schistocytes, which might suggest another diagnosis
Coombs’ test If an autoimmune-mediated thrombocytopenia is suspected
Antigen testing of mother’s and father’s platelets with testing of mother’s serum for antiplatelet alloantibody If neonatal alloimmune thrombocytopenia is suspected
Transcranial ultrasound Indicated in all severely thrombocytopenic (<30,000/μL) neonates to evaluate for intracranial hemorrhage
Prothrombin time, activated partial thromboplastin time, plasma fibrinogen concentration, fibrin degradation product, D-dimer If disseminated intravascular coagulation (DIC) is suspected. In DIC, prothrombin time is prolonged, activated partial thromboplastin time is prolonged, plasma fibrinogen concentration is decreased, fibrin degradation product is increased, and D-dimer is elevated.

Additional Work-up

Identification and treatment of the underlying cause is indicated if a primary disease process is suspected in cases of neonatal thrombocytopenia. Infants who appear ill should be evaluated for sepsis. Evaluation for congenital infection or genetic testing may be indicated.

Bone marrow examination Indicated for any child with thrombocytopenia with an atypical presentation or with thrombocytopenia lasting for longer than 6 months to evaluate for other conditions that could result in thrombocytopenia
Maternal platelet count To distinguish alloimmune thrombocytopenia from autoimmune thrombocytopenia

References

1. Bolton-Maggs H.B. Idiopathic thrombocytopenic purpura. Arch Dis Child. 2000;83:220–222.

2. Cines D.B., Blanchette V.S. Immune thrombocytopenic purpura. N Engl J Med. 2002;346:995–1008.

3. Kaplan R.N., Bussel J.B. Differential diagnosis and management of thrombocytopenia in childhood. Pediatr Clin North Am. 2004;51:1109–1140.

4. Roberts I., Murray N.A. Neonatal thrombocytopenia: causes and management. Arch Dis Child Fetal Neontal Educ. 2003;88:359–364.

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