Beyond the Glomerulus With Antineutrophil Cytoplasmic Antibody-Associated Vasculitis.

Typical renal involvement of antineutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is pauci-immune glomerulonephritis that presents clinically as rapidly progressive renal failure (RPRF). Here, we report an unusual presentation of myeloperoxidase (MPO)-specific ANCA with isolated involvement of the tubulointerstitium in the form of peritubular capillaritis as the sole lesion without any involvement of the glomerulus. A 52-year-old woman with no previous comorbidities presented with nonspecific symptoms such as fatigue, dysuria, and nausea for two months. On evaluation, we found that she had renal failure (serum creatinine around 3-4 mg/dL) and numerous urinary pus cells with a sterile urine culture. We treated her with empirical antibiotics cover for culture-negative urinary tract infections. In view of nonresolving renal failure, we conducted a further evaluation and found that she had positive serum MPO titers, and renal biopsy revealed isolated tubulointerstitial involvement of the kidney with glomerular sparing in the form of acute interstitial nephritis (AIN). We observed peritubular capillaritis. We ruled out alternative explanations for AIN such as drug use and infections and attributed the peritubular capillaritis to the high titers of MPO positivity. We started her on steroids and mycophenolate mofetil (MMF) after ruling out infection. Over the next few months, she improved clinically and attained remission. Her creatinine reduced to within normal limits, and her MPO-ANCA titers became negative. She is currently on follow-up and doing well. The rarity of the entity should be considered when evaluating cases of AIN.