Collapsing Focal Segmental Glomerulosclerosis With Anti-nephrin Antibody Following Minimal Change Disease Possibly Triggered by COVID-19 Infection: A Case Report

A man in his forties experienced foamy urine after COVID-19 infection and received a kidney biopsy. He received tacrolimus for myasthenia gravis; no kidney disease was noted before COVID-19 infection, and he had no family history of kidney disease. The biopsy showed minimal change disease, characterized by IgG deposition in the podocyte and mesangial areas. Prednisone was started at 70 mg, but he required hemodialysis three months after COVID-19 infection. A second biopsy 15 months after the COVID-19 infection showed collapsing focal segmental glomerulosclerosis (FSGS) with IgG deposition in the podocytes and mesangium. Immunofluorescence imaging of the second biopsy using structure illumination microscopy showed decreased nephrin expression and punctuate IgG deposition colocalized with nephrin. Thereafter, his serum was positive for anti-nephrin antibodies (367 IU/ml, cut-off 226 U/ml). To the best of our knowledge, no other reports of collapsing FSGS or minimal change disease with anti-nephrin antibodies triggered by COVID-19 infection have been published. This case summarizes a novel case of collapsing FSGS with IgG-positive podocytes associated with anti-nephrin antibodies following minimal change disease, possibly triggered by COVID-19 infection. Further study is needed to clarify the mechanism by which anti-nephrin antibodies are produced by COVID-19 infection.