Nephropathy associated with IgG4-related disease is characterized by tubulointerstitial nephritis. To better identify its pathology, the present study analyzed clinicopathologic features of IgG4-related tubulointerstitial nephritis cases from across Japan. Sixteen cases were identified as IgG4-related nephropathy using the criterion of high serum IgG4 levels (>135 mg/dL) with abnormal kidney computed tomography or elevated serum creatinine levels. Male predominance (75%) and advanced age (average, 62.0 years) were noted. Eight cases displayed no autoimmune pancreatitis. Renal computed tomography abnormalities were found in 12 of 13 cases examined. Renal dysfunction was found in 15 of 16 cases at biopsy. Distinctive features of tubulointerstitial lesions included (1) well-demarcated borders between involved and uninvolved areas; (2) involvement of the cortex and medulla, often extending beyond the renal capsule and with occasional extension to retroperitoneal fibrosis; (3) interstitial inflammatory cells comprising predominantly plasma cells and lymphocytes, with a high prevalence of IgG4-positive cells often admixed with fibrosis; (4) peculiar features of interstitial fibrosis resembling a "bird's-eye" pattern comprising fibrosis among inter-plasma cell spaces; and (5) deposits visible by light and immunofluorescent microscopy in the tubular basement membrane, Bowman capsule, and interstitium that are restricted to the involved portion, sparing normal parts. Ultrastructural analysis revealed the presence of myofibroblasts with intracellular/pericellular collagen accompanied by plasma cell accumulation from an early stage. Histology could not discriminate between IgG4-related tubulointerstitial nephritis with and without autoimmune pancreatitis. In conclusion, the distinctive histologic features of IgG4-related tubulointerstitial nephritis can facilitate the differential diagnosis of tubulointerstitial nephritis, even without autoimmune pancreatitis or an abnormal computed tomography suggesting a renal tumor.
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