Background
Idiopathic thrombocytopenic purpura (ITP), also known as primary immune thrombocytopenic purpura and autoimmune thrombocytopenic purpura, is defined as isolated thrombocytopenia with normal bone marrow and in the absence of other causes of thrombocytopenia. ITP has two distinct clinical syndromes, manifesting as an acute condition in children and a chronic condition in adults.
Pathophysiology
ITP is primarily a disease of increased peripheral platelet destruction, with most patients having antibodies to specific platelet membrane glycoproteins. Relative marrow failure may contribute to this condition, since studies show that most patients have either normal or diminished platelet production.
Acute ITP often follows an acute infection and has a spontaneous resolution within 2 months. Chronic ITP persists longer than 6 months without a specific cause.
Epidemiology
Frequency
United States
Incidence rates are as follows:
- The incidence of ITP in adults is approximately 66 cases per 1,000,000 per year.
- An average estimate of the incidence in children is 50 cases per 1,000,000 per year.
- New cases of chronic refractory ITP comprise approximately 10 cases per 1,000,000 per year.
International
According to studies in Denmark and England, childhood ITP occurs in approximately 10-40 cases per 1,000,000 per year. A prospective, population-based study in Norway indicated an incidence of 53 per 1,000,000 in children younger than 15 years. A study in Kuwait reported a higher incidence of 125 cases per 1,000,000 per year.
Mortality/Morbidity
Hemorrhage represents the most serious complication; intracranial hemorrhage is the most significant. The mortality rate from hemorrhage is approximately 1% in children and 5% in adults. In patients with severe thrombocytopenia, predicted 5-year mortality rates from bleeding are significantly raised in patients older than age 60 and those under age 40 -- 47.8% versus 2.2%, respectively. Older age and previous history of hemorrhage increase the risk of severe bleeding in adult ITP.
Spontaneous remission occurs in more than 80% of cases in children. However, it is uncommon in adults.
Age
See the list below:
- Peak prevalence occurs in adults ages 20-50.
- Peak prevalence occurs in children ages 2-4.
- Approximately 40% of all patients are younger than age 10.
Sex- and Age-related Demographics
In chronic ITP (adults), the female-to-male ratio is 2.6:1. More than 72% of patients older than age 10 are female. In acute ITP (children), distribution is equal between males (52%) and females (48%).
In adults, the peak prevalence is from ages 20 to 50. In children, peak prevalence is from ages 2 to 4. Approximately 40% of all patients are younger than age 10.