Background/Purpose: Only a few reports have focused on the rate of renal function deterioration in IgG4-related tubulointerstitial nephritis (IgG4-TIN). Some cases show acute or progressive chronic renal failure, and others progression of renal failure slowly over one year or more. This study aimed to investigate the rate of renal function deterioration in patients with biopsy proven IgG4-TIN, leading to clarification of the divergence of the deterioration rate of renal function, identifying the factors affecting the deterioration rate, and confirming the influence of the deterioration rate on the final renal function of each case.

Methods: We extracted 18 patients with IgG4-TIN between July 2006 and March 2017 in four hospitals. Based on the rate of renal function deterioration using estimated glomerular filtration rate (eGFR) before starting corticosteroid therapy, we divided them into a rapidly deteriorating group (deterioration rate more than or equal to 4 ml/min/1.73m²/month) (n=8) and a slowly deteriorating group (deterioration rate less than 4 ml/min/1.73m²/month) (n=10), and retrospectively analyzed various clinical features (age, sex, serum IgG levels, serum IgG4 levels, serum IgE levels, serum complement levels, serum eGFR levels at start of corticosteroid and the last visit, initial dose of prednisolone, multiple organ lesions) during the clinical course in the two groups.

Results: The mean age of the 18 patients was 69 years (range: 43 to 81 years). 89% of the patients were male. The average number of affected organs was 4 (range: 1 to 9). All patients had elevated serum IgG4 levels, and average was 977 mg/dL (range: 207 to 2800). In all patients, the diagnosis of IgG4-TIN was made by histopathological confirmation of the kidney biopsy specimen with immunostaining. The mean kidney function decline rate per month before starting corticosteroid therapy was 4.4 ml/min /1.73m²/month. In seven cases, the deterioration rate of kidney function was less than 2 ml/min/1.73m²/month, while 10 cases had a rapid deterioration rate more than 4 ml/min/1.73m²/month. Corticosteroid was effective in all cases, and average recovery of eGFR after corticosteroid therapy was 17.4 ml/min/1.73m² (range: -0.4 to 46.5). In group A (a slowly deteriorating group), the recovery of eGFR was less than that in group B (a rapidly deteriorating group) (6.4 ml/min/1.73m² vs. 26.3 ml/min/1.73m², P < 0.05). Hypocomplementemia was more frequent in patients in group A than those in group B (P < 0.05). No differences were noted regarding gender, age, eGFR before starting corticosteroid therapy, eGFR at the last visit, the number of affected organs, eosinophil count, serum IgG levels, IgG4, or IgE between the groups.

Conclusion: Regarding the deterioration rate of renal function before corticosteroid therapy in patients with IgG4-TIN, there are two groups, i.e. a rapidly deteriorating group and slowly deteriorating group. Hypocomplementemia is associated with the rapid deterioration of renal function, and a slowly deteriorating group shows lower recovery of renal function after the corticosteroid therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/multicenter-study-on-the-rate-of-renal-function-deterioration-in-igg4-related-tubulointerstitial-nephritis/