The Case | Idiopathic hypocomplementemic interstitial nephritis

A 70-year-old male with chronic kidney disease stage 3 developed increasing peripheral edema and a progressive renal insufficiency over 6 months. This was associated with hypertension (168/98 mm Hg) and hematoproteinuria (urine protein creatinine ratio of 381 mg/g). The serum creatinine reached a peak of 3.3 mg/dl. There was no history of weight loss, fever, or infections. He did not have any history of skin rashes, arthralgia, or hair loss. There was no evidence of any exposure to non-steroidal anti-inflammatory drugs, herbal medicines, or over-the-counter medications. Physical examination was unremarkable, except for the presence of bilateral leg edema. Similarly there was no evidence of skin rashes, arthropathies, or lymphadenopathy. There was a past medical history of two similar episodes over the last 3 years. On both occasions, renal biopsies were obtained and revealed tubulointerstitial nephritis with uncertain etiologies. Therapy with corticosteroids led to improvement in renal excretory function. Laboratory studies showed severe hypocomplementemia (C4 0.02, 0.14–0.54 mg/ml, C3 0.77, 0.75–1.65 mg/ml) and high anti-C1q antibody (105 U/ml, 0–15). Serum complement levels were not checked prior to previous biopsies. Serum levels for ANA, anti-dsDNA, anti-cardiolipin antibodies, lupus anticoagulant, and cryoglobulins were unremarkable. Imaging studies including chest X-ray, renal ultrasound, and transthoracic echocardiogram were all normal. Computed tomography scan of chest, abdomen, and pelvis showed no abnormalities in kidneys, pancreas, liver, spleen, or lungs nor presence of lymphadenopathy. A renal biopsy was performed (Figure 1).



Figure 1. Renal biopsy findings. (a) Light microscopy shows intraglomerular microthrombi (Martius, Scarlet Blue stain, magnification × 40). (b) Tubulointerstitial inflammation with predominant plasma cell infiltration (hematoxylin & eosin stain, magnification × 20). (c) Electron microscopy shows fragmentation of tubular basement membrane with immune deposits.