Long-term preserved renal function of a patient with mass-forming granulomatous interstitial nephritis by biopsy-based steroid therapy

In 2001, a 41-year-old Japanese woman was referred to our hospital because of severe renal dysfunction and fever of unknown origin. On admission, her serum creatinine was 8.7 mg/dL, urine protein was 0.3 g/day, and urine β₂-microglobulin was 81,007 μg/day. Computed tomography (CT) scans showed bilateral contracted kidneys with a mass projecting from the lower pole of the right kidney. Biopsy of this lesion revealed interstitial nephritis and a noncaseating granuloma. Because extrarenal organ involvement or laboratory findings specific for sarcoidosis or other primary diseases were not detected, idiopathic granulomatous interstitial nephritis (GIN) was diagnosed. Prednisolone was started at dosage of 30 mg daily, and serum creatinine decreased to 5.5 mg/dL after 1 month. Her renal function was preserved for 8 years, but maintenance hemodialysis had to be started in 2009. A surgical specimen obtained after initiation of dialysis showed resolution of GIN in the renal mass lesion, which presumably resulted in preservation of renal function over the long term. Even in patients with severe renal dysfunction, histological diagnosis of GIN might lead to prognostic improvement because of appropriate therapeutic intervention.