Post-varicella thrombocytopenic purpura

Aims: The aim of the study was to characterize the clinical course of post-varicella idiopathic thrombocytopenic purpura (ITP) and to asses the risk of acquiring ITP after varicella infection. Methods: A retrospective study of all children diagnosed with ITP in a tertiary medical centre during 1998-2008. Findings were compared with the Intercontinental Childhood ITP Study Group database. The risk of acquiring ITP after a varicella infection was assessed. Results: Ten children were diagnosed with post-varicella ITP. The incidence of post-varicella ITP was 1.9% amongst children diagnosed with ITP and 1.1% amongst children hospitalized for varicella. ITP was diagnosed, on average, 8.5 days after the onset of the varicella rash. The female-to-male ratio was 1:1.5. The average minimal platelet count was 9.5 x 109 platelets/L. Post-varicella ITP had an acute course in 80% of cases and a chronic course in the remaining 20%. Bleeding episodes occurred in three patients. During the follow-up period, 11 patients with previously diagnosed ITP developed varicella. The infection had no apparent affect on the platelet count of the children with acute ITP, but caused a relapse in 71% of the patients with chronic ITP. Conclusions: Post-varicella ITP has similar clinical features and course to non-varicella associated ITP. The calculated risk of ITP as a complication of varicella infections is approximately 1:25 000.