A 74-year-old man was hospitalized for diabetic nephropathy evaluation and assessment of the effect of treatment on his tubulointerstitial nephritis (TIN). When he was 62 years old, he developed polyarthralgia and had superficial lymph node swelling, mildly increased serum creatinine concentration, hypergammaglobulinemia, hypocomplementemia, high serum IL-2R level, and positive titer of antinuclear antibody. Several tissues were biopsied. Mild chronic sialadenitis and reactive lymphadenitis were identified. Renal specimen showed mild glomerular ischemia, extensive storiform fibrosis, and abundant infiltrating monocytes and plasma cells. He was treated with oral prednisolone and cyclophosphamide. After the treatment, most of his clinical parameters quickly returned to within the reference range. However, he developed diabetes mellitus soon after steroid therapy. At the time of rebiopsy, a high level of serum IgG4 was detected. The second renal biopsy showed diabetic nephropathy without any tubulointerstitial damage. The first biopsied tissues were retrospectively investigated. Large numbers of IgG4-positive plasma cells were detected in the kidneys and lymph nodes. A retrospective diagnosis of IgG4-related TIN with lymph node involvement was made. In conclusion, this paper describes a retrospectively diagnosed case of IgG4-related TIN with lymph node involvement, showing good clinical and pathological prognosis. 1. Introduction With the increase in reports of cases of IgG4-related diseases (IgG4-RDs) such as IgG4-related kidney disease (IgG4-RKD), autoimmune pancreatitis, sialadenitis, and retroperitoneal fibrosis [1–9], the All Japan IgG4 team has established comprehensive diagnostic criteria for IgG4-RD [1]. The critical parameters are serum IgG4 level and the quantity of tissue-infiltrating IgG4-positive cells, which are defined as >135？mg/dL and >10 IgG4-positive cells/high-power field (HPF) and/or >40% IgG4/IgG-positive cell ratio, respectively. IgG4-RKD mostly affects the tubulointerstitium and induces tubulointerstitial nephritis (TIN) [2, 3]. IgG4-related TIN differs from non-IgG4-related TIN in that it shows characteristic storiform fibrosis and massive IgG4-positive plasma cell infiltration. However, before the concept of IgG4-RD was established, some cases with the above features could not be classified as IgG4-RD. Here, we report a case that was diagnosed as TIN with interstitial fibrosis 12 years ago and was retrospectively diagnosed as IgG4-related TIN with lymph node involvement. Meaningfully, the storiform fibrosis and infiltrating cells
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