• Shohei Noda, Shintaro Mandai, Takashi Oda, Tomoko Shinoto, Hidehiko Sato, Keiko Sato, Katsuiku Hirokawa, Yumi Noda, and Shinichi Uchida.
• Department of Nephrology, Nitobe Memorial Nakano General Hospital, Nakano.
• Medicine (Baltimore). 2020 Jun 19; 99 (25): e20572.

RationaleInfection is a major trigger or pathogenic origin in a substantial proportion of glomerulonephritis (GN) patients, typically manifesting infection-related GN (IRGN). Various microorganisms, infection sites, and clinical and histopathological features are involved in IRGN. Once an infectious origin is identified and successfully eradicated, nephrotic syndrome or kidney dysfunction is spontaneously resolved. However, if patients are asymptomatic and the origin is undetermined, the diagnosis and treatment of GN is challenging. This case presentation reported on an IRGN case manifesting steroid-resistant nephrotic syndrome associated with asymptomatic sinusitis as a pathogenic origin.Patient ConcernsA 68-year-old male presented with severe kidney dysfunction and edema in both extremities.DiagnosisThe patient was clinically diagnosed with hypocomplementemic nephrotic syndrome and kidney dysfunction and histopathologically with diffuse proliferative GN and a focal pattern of membranoproliferative GN. The findings suggested that idiopathic membranoproliferative glomerulonephritis type I was more likely than IRGN, given a critical lack of apparent infection.InterventionsCombined intravenous methylprednisolone, oral prednisolone, and cyclosporin did not improve the patient's condition. Thus, IRGN associated with inapparent infectious origin was suspected. Repeated thorough and careful examinations including CT scan showed sinusitis in his left maxillary sinus. Moreover, reanalysis of kidney specimen revealed positive nephritis-associated plasmin receptor in glomeruli, a typical finding for IRGN, supporting a pathogenic significance of his sinusitis. Medical treatment was initiated with 200 mg oral clarithromycin daily.OutcomesOral clarithromycin gradually improved proteinuria and hypocomplementemia and resulted in nephrotic syndrome remission in parallel with opacification resolution of sinuses shown on CT.LessonsThis case presentation showed that asymptomatic sinusitis is potentially a pathogenic IRGN origin. A gold standard therapy for idiopathic GN, corticosteroid could be damaging in uncontrolled or underdiagnosed infection. In asymptomatic patients, a thorough screening of infectious diseases, including sinusitis, together with a renal histological evaluation of glomerular nephritis-associated plasmin receptor deposition is also essential in treating a wide spectrum of GN.

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