IgG4-Related Kidney Disease: A Diagnostic Conundrum Successfully Treated With Steroids and Rituximab.

IgG4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory condition that has been recognized as a unified systemic disease that links many individual organ conditions that were previously considered to be unrelated. The pathological hallmark of the disease is an abundant IgG4-positive plasma cell infiltration in the affected tissues and fibrosis. It is a great mimicker of neoplastic, inflammatory, and infectious conditions. We report a 72-year-old man who presented to our hospital with dyspnea and oliguria. Detailed evaluation revealed that he was treated at multiple places for right-sided loin pain over the past 10 months and was found to have right-sided hydronephrosis, renal dysfunction, and multiple enlarged lymph nodes. A search for underlying malignancy previously was unyielding and he had rapid worsening of renal function prior to the current presentation. He was uremic and was initiated on hemodialysis. Kidney biopsy revealed features of IgG4-related tubulointerstitial nephritis. Despite tubular atrophy and interstitial fibrosis involving more than 50% of the sampled cortex, he showed a good response to steroids and rituximab (RTX) and became dialysis-independent. This report underscores the masquerading presentation of IgG4-RD which can hinder timely diagnosis and demonstrates the usefulness of a regimen of steroids and RTX in its treatment.