Interstitial nephritis with moderate-to-heavy proteinuria: An unusual combination

Interstitial nephritis with proteinuria >1 g/day is uncommon and almost always the result of drug-induced ATIN with an associated minimal change glomerulonephritis (GN). Here, we present a series of five unusual cases of interstitial nephritis without GN but with proteinuria >1 g/day, and they were identified from renal biopsies done from February 2008 to March 2009. Out of 236 patients who underwent renal biopsy, only five met the inclusion criteria. Three patients presented with edema and two with oliguria, while none had frank hematuria, fever, arthralgia, skin rash or history of exposure to nonsteroidal antiinflamatory drugs, analgesics, anti­biotics, allopurinol, or Chinese herb before presentation. Urinalysis revealed hematuria in two patients, pyuria in three and nephrotic range proteinuria in two. All had normal complement levels and were negative for antinuclear antibodies, Anti-dsDNA antibody, and antineutrophil cyto-plasmic antibodies. Clinical diagnosis was nephrotic syndrome in two patients, the third had diagnosis of rapidly progressive GN, the fourth had HIV associated nephropathy, and the fifth had unexplained advanced renal failure. Though three patients had renal dysfunction only one required dialysis. Light microscopy of renal biopsies revealed granulomatous interstitial nephritis in three patients and small vessel vasculitis in two of them. One patient had nongranulomatous interstitial nephritis along with vasculitis. Acute interstitial nephritis was the only finding in one patient. In conclusion, patients with interstitial nephritis can present with moderate-to-heavy proteinuria probably due to cytokine-like permeability increasing factor secreted by inflammatory cells in the interstitium.