An Unusual Case of Persistent Isolated Proteinuria: Postinfectious Glomerulonephritis in a Patient with Diabetes with Diffuse Cutaneous Systemic Sclerosis

Introduction: Diffuse cutaneous systemic sclerosis (dcSSc) is an autoimmune disorder characterized by vascular dysfunction and fibrosis of the skin and internal organs. Renal involvement in patients with coexisting diabetes presents diagnostic challenges, particularly when persistent isolated proteinuria is the main clinical feature. Case Description: A 60-year-old man with dcSSc and diabetes present with foamy urine for 2 months, along with worsening skin thickening and progressive Raynaud phenomenon. His medications included cyclophosphamide 25 mg/day, amlodipine, and metformin. On examination, his blood pressure was 139/82 mmHg with hypopigmented sclerotic plaques on the face and chest. Laboratory tests showed microangiopathic hemolytic anemia, negative direct antiglobulin test, serum creatinine 1.14 mg/dL (eGFR 69.51 mL/min/1.73 m2), albumin 3.0 g/dL, cholesterol 144 mg/dL, and HbA1c 4.77%. Urinalysis showed progression from trace to 4+ proteinuria, with a random urine protein excretion of 4 g/day and no active sediment. Complement levels were normal. ANA was positive (1:1280, homogeneous and nucleolar); anti-dsDNA was negative, and anti-Scl-70 was positive. Renal ultrasound showed bilateral parenchymal disease. After increasing cyclophosphamide to 50 mg/day and adding prednisolone 10 mg/day for 1 month, there was no improvement in proteinuria. Kidney biopsy revealed nodular sclerosis with subepithelial hump-like deposits and moderate arteriolar hyalinosis. Immunofluorescence showed diffuse global mesangial and capillary loop staining in a “starry sky” pattern for IgG (2+) and C3 (3+). These findings were consistent with late post-infectious glomerulonephritis (PIGN) superimposed on class II diabetic nephropathy. Management included supportive care for PIGN and glycemic control to slow chronic kidney disease progression. Discussion: PIGN can occur in dcSSC patients with active skin disease. Though typically managed supportively, timely recognition is essential to guide immunosuppressive therapy and improve renal outcomes in patients with multi-organ involvement.