The incidence and severity of Henoch-Schönlein purpura nephritis over a 22-year period in Fukushima Prefecture, Japan.

Background: Recently, there have been a few reports on the decrease in the incidence of severe Henoch-Schönlein purpura nephritis (HSPN) in Japan. To evaluate the incidence and the severity of HSPN, we examined the epidemiology and clinical manifestations of HSPN in Fukushima Prefecture over a 22-year period.
Methods: We enrolled 61 patients (Group 1) diagnosed with HSPN between 1987 and 1997 and a further 59 patients (Group 2) diagnosed with HSPN between 1998 and 2008. Epidemiology, clinical features, laboratory data, pathological findings, treatment and outcome were retrospectively compared between the two groups.
Results: The mean number of patients per 100,000 children per year was 3.5 ± 1.2 in Group 1 and 3.6 ± 0.8 in Group 2. The clinical manifestations and laboratory findings at onset were comparable between Groups 1 and 2. Pathological findings in Group 1 and Group 2 were classified as ISKDC grade IIIa in 16 (26%) and 14 cases (24%), grade IIIb in 26 (43%) and 27 cases (46%), grade IV in 5 (8%) and 6 cases (10%)), grade V in 1 (2%) and 5 cases (8%), and grade VI in 2 (3%) and 2 cases (3%), respectively. There were no inter-group differences in ISKDC classification or rate of crescentic formation.
Conclusions: Our findings suggest that the incidence of HSPN and the severity of HSPN in patients between 1987 and 1997 were similar to those in patients between 1998 and 2008 and that the number of patients with severe HSPN has not decreased.