Case Report: Clinical insights into IgG4-related nephropathy with overlapping syndrome: a review of two cases

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is characterized by small-vessel inflammation, whereas immunoglobulin G4-related disease (IgG4-RD) is typified by fibrosis, dense lymphoplasmacytic infiltration, and the presence of IgG4-positive plasma cells. The overlapping clinical, serological, radiological, and histopathological features between these distinct entities pose significant diagnostic challenges, frequently culminating in poor prognoses for elderly patients with concurrent diabetes mellitus. Herein, we report two cases of IgG4-related tubulointerstitial nephritis (IgG4-TIN). Case 1 describes a 77-year-old diabetic male exhibiting concurrent features of proteinase 3 (PR3)-positive AAV (including pulmonary lesions, hematuria, and rapid renal function decline) and IgG4-TIN, further complicated by chronic heart failure and peripheral neuropathy. The patient demonstrated a suboptimal therapeutic response to standard regimens of corticosteroids and monoclonal antibodies. Case 2 involves a patient presenting with mass-forming retroperitoneal fibrosis that led to obstructive uropathy and acute kidney injury. Of particular clinical note, Case 1 was complicated by an inadvertent lumbar artery puncture during renal biopsy, which precipitated hemorrhagic shock requiring urgent transcatheter arterial embolization. This comparative analysis elucidates the diagnostic and therapeutic complexities of IgG4-nephropathy in elderly, comorbid populations, while also underscoring the critical management of rare, life-threatening procedural complications.