Definition of Immune Thrombocytopenic Purpura (ITP)
Immune Thrombocytopenic Purpura (ITP) is an autoimmune disorder characterized by immunologic destruction of otherwise normal platelets, defined as a platelet count less than 100 × 10^9/L in the absence of other causes or disorders that may cause thrombocytopenia. 1
Primary vs Secondary ITP
ITP is classified into two main categories:
- Primary ITP: Occurs in isolation without an identifiable underlying cause
- Secondary ITP: Occurs in association with other disorders, including:
- Autoimmune diseases (particularly antiphospholipid antibody syndrome)
- Viral infections (including hepatitis C and HIV)
- Certain medications 1
Pathophysiology
The understanding of ITP pathophysiology has evolved over time:
- Traditional view: ITP was believed to be caused primarily by increased platelet destruction exceeding the bone marrow's compensatory production
- Current understanding: Evidence shows that platelet production is also decreased in many patients with ITP 1
Classification Based on Duration
ITP is categorized based on the duration of thrombocytopenia:
- Newly diagnosed: Within 3 months of diagnosis
- Persistent ITP: 3-12 months from diagnosis
- Chronic ITP: Lasting ≥12 months 2
Diagnostic Approach
The diagnosis of ITP is primarily one of exclusion:
Essential diagnostic tests:
- Complete blood count with differential
- Peripheral blood smear examination
- Reticulocyte count
- HIV and HCV testing 2
Peripheral blood smear findings consistent with ITP:
- Thrombocytopenia with normal to slightly larger platelets (but not giant platelets)
- Normal red blood cell morphology
- Normal white blood cell morphology 1
Findings not consistent with ITP:
- Red blood cell poikilocytosis or schistocytes
- Predominant giant platelets
- Leukocytosis or leukopenia with immature or abnormal cells 1
Bone Marrow Examination
- Not routinely necessary in children and adolescents with typical features of ITP
- Not necessary in children who fail IVIg therapy
- Generally not needed prior to initiation of corticosteroid treatment or before splenectomy 1
Clinical Presentation
ITP can present with:
- Petechiae and purpura
- Easy bruising
- Mucosal bleeding (e.g., epistaxis, gingival bleeding)
- In severe cases, internal bleeding including intracranial hemorrhage (rare, occurring in 0.1-0.5% of children with ITP) 2
Distinguishing Features
It's important to note that ITP is distinguished from other thrombocytopenias by:
- Normal bone marrow with adequate to increased megakaryocytes
- Absence of splenomegaly (though spleen may be palpable in approximately 12% of children with ITP) 1
- Absence of other causes of thrombocytopenia based on history, physical examination, and laboratory testing 3
The definition and understanding of ITP have evolved significantly since the initial ASH guidelines in 1996, with updated terminology and diagnostic criteria established by the International Working Group consensus panel of both adult and pediatric experts in ITP 1.