Estimation of the number of histological diagnosis for IgG4-related kidney disease referred to the data obtained from the Japan Renal Biopsy Registry (J-RBR) questionnaire and cases reported in the Japanese Society of Nephrology Meetings

Background More than 2 years have passed since the proposal of the diagnostic criteria for IgG4-related kidney disease (IgG4-RKD). The aim of this study was to estimate the number of histological diagnosis for IgG4-RKD throughout Japan and to clarify the regional distribution of the development of this disease. Methods A questionnaire was supplied to 140 research facilities registered in the Japan Renal Biopsy Registry (JRBR). The items of the questionnaire were the total number of renal biopsies performed and the number of cases diagnosed as IgG4-RKD in 2012 and 2013 at each facility. Age, sex, and diagnosis category were also included for the IgG4-RKD cases. The geographic distribution of the disease development was evaluated using clinical case reports presented at the Eastern/Western regional meeting of the Japanese Society of Nephrology during the 15 years following 2001. Results Forty-seven facilities completed the questionnaire, resulting in a collection rate of 34 %. The total numbers of renal biopsies in 2012 and 2013 were 3387 and 3591, respectively. Forty-seven of these cases (24 in 2012 and 23 in 2013) were diagnosed as IgG4-RKD. The frequency of development of IgG4-RKD per one million over 40-year-old individuals during these 15 years varied between 0.9 and 3.1, depending on Japanese geographic region of Japan. Conclusion The results of the present survey indicate that the number of diagnosis for IgG4-RKD is approximately 130 cases per year throughout Japan, and no regional differences in disease frequency appear to exist.