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 × 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.