Sequential Treatment With Corticosteroids and Cyclosporine A in a High-Risk Patient With IgG-Negative Immunotactoid Glomerulopathy

Immunotactoid glomerulopathy (ITG) is a rare glomerular disease characterized by organized microtubular deposits and is frequently associated with hematologic malignancies. Diagnosis is typically supported by IgG-positive staining on immunofluorescence together with characteristic ultrastructural findings on electron microscopy. However, diagnostic difficulties may arise when immunofluorescence findings are atypical. We report the case of an 82-year-old woman who presented with nephrotic syndrome and progressive renal dysfunction, with proteinuria of 13.8 g/g creatinine, a serum creatinine level of 2.33 mg/dL, and an estimated glomerular filtration rate of 16.0 mL/min/1.73 m². Serum and urine immunoelectrophoresis revealed no evidence of monoclonal proteins. Renal biopsy demonstrated mesangial proliferative glomerulonephritis with negative IgG staining on immunofluorescence. The diagnosis of ITG was ultimately established by electron microscopy, which revealed organized hollow microtubular structures measuring 30 to 90 nm in diameter within the mesangial and subepithelial regions. Based on the presence of hypertension, nephrotic-range proteinuria, and impaired baseline renal function, the patient was considered to be at high risk for progression to end-stage renal disease. No underlying hematologic malignancy was identified. Treatment with corticosteroids followed by cyclosporine A (CsA) resulted in a favorable clinical response. By day 364, the patient achieved near-complete remission with proteinuria decreasing to 0.24 g/g creatinine and eGFR stabilizing at 25.4 mL/min/1.73 m². This case underscores the importance of considering ITG when characteristic ultrastructural findings are present, even in the absence of IgG positivity on immunofluorescence. Furthermore, this case may represent one of the first reported instances in which treatment with prednisolone and CsA was effective in a high-risk patient with ITG without an identifiable clonal disorder.