PODOCYTE INFOLDING GLOMERULOPATHY ASSOCIATED WITH SYSTEMIC LUPUS ERYTHEMATOSUS: A CASE INITIALLY TREATED AS MINIMAL CHANGE NEPHROTIC SYNDROME

Podocyte infolding glomerulopathy (PIG) is an extremely rare glomerular disease characterized by electron microscopy findings showing podocyte foot process infolding into the glomerular basement membrane (GBM), accompanied by microspheres or microtubular structures within the GBM. It is often associated with autoimmune diseases, particularly systemic lupus erythematosus (SLE). Misdiagnosis as membranous nephropathy can occur, and electron microscopy is essential for diagnosis. We report a case initially treated as minimal change nephrotic syndrome (MCNS), which relapsed and was later diagnosed as PIG upon reevaluation of electron microscopy. 

A 43-year-old woman presented with abdominal pain, vomiting, and diarrhea in January 2022. Despite conservative treatment at a local clinic, her symptoms persisted. CT revealed mild gastric wall thickening, marked small-bowel wall thickening, and mild ascites, leading to referral to the gastroenterology department in February 2022. Contrast-enhanced CT revealed edema extending from the jejunum to the colon. Laboratory tests revealed hypoalbuminemia (2.4 g/dL) and a urine protein-to-creatinine ratio (UPCR) of 7.83 g/gCr, suggesting nephrotic syndrome (NS) as the cause of her gastrointestinal symptoms. She was transferred to nephrology, and kidney biopsy confirmed MCNS. Prednisolone (45 mg/day, 0.8 mg/kg/day) was initiated, and cyclosporine 50 mg/day was added. UPCR decreased to 1.59 g/gCr at 19 days after starting prednisolone. She was discharged on day 39 and continued tapering therapy as an outpatient. After achieving remission (UPCR <0.3 g/gCr) in August 2022, prednisolone and cyclosporine were discontinued in February and July 2024, respectively. Although gastrointestinal symptoms recurred in August 2024 with CT findings similar to the initial episode, her symptoms improved with conservative care. However, UPCR rose above 1.0 g/gCr and serum albumin declined, though remained >3.0 g/dL without immunosuppressive treatment. In July 2025, gastrointestinal symptoms recurred, prompting readmission. Given the atypical course for MCNS, the 2022 biopsy was re-examined, revealing PIG with electron microscopy features of microspheres within GBM. Laboratory findings showed Antinuclear antibody 1:160, anti-SS-A antibody 1200 IU/mL, and hypocomplementemia (C3 57 mg/dL), suggesting SLE. In August 2025, gastrointestinal symptoms flared again, and contrast-enhanced CT revealed bowel wall thickening and fluid retention from the small intestine to the colon, suggesting lupus enteritis. UPCR increased to 19.74 g/gCr. Induction therapy with prednisolone (50 mg/day, 1 mg/kg/day), mycophenolate mofetil (500 mg/day) and hydroxychloroquine (200 mg/day) was initiated, followed by tacrolimus (2 mg/day) because of persistent nephrotic-range proteinuria. UPCR declined to 1.27 g/gCr, and she was discharged on day 35 with plans for outpatient follow-up care. 

This case highlights the diagnostic challenge of PIG, which was initially misdiagnosed as MCNS. Reevaluation of electron microscopy was crucial for accurate diagnosis. Although no specific treatment for PIG exists, immunosuppressive therapy targeting underlying SLE improved proteinuria and abdominal symptoms. This case suggests that clinicians should re-examine renal pathology when NS follows an atypical course.