Immunotactoid Glomerulopathy Diagnosed by a Repeat Kidney Biopsy After Initially Non-diagnostic Electron Microscopic Findings: A Case Report.

Immunotactoid glomerulopathy (ITG) is diagnosed by identifying organized microtubules on electron microscopy and it can therefore be missed when they are not demonstrated. A 48-year-old woman with hematuria, nephrotic-range proteinuria, and a faint IgG-κ monoclonal protein underwent an initial kidney biopsy, which showed endocapillary proliferative glomerulonephritis with membranoproliferative features and scant subendothelial deposits, but no diagnostic microtubules. With worsening renal dysfunction and a limited corticosteroid response, a repeat biopsy revealed IgG3-κ-restricted deposits and non-branching, hollow-core microtubules, confirming ITG associated with monoclonal gammopathy of renal significance. Rituximab-based B cell-directed therapy was followed by sustained remission with prednisolone tapered to 2.5 mg every other day.