A case of neuron-derived neurotrophic factor-positive, syphilis-related membranous nephropathy that achieved spontaneous remission

Neuron-derived neurotrophic factor (NDNF) was discovered as a target antigen in membranous nephropathy (MN) caused by syphilis. However, there have been few reports of NDNF-positive MN in Japan. A 19-year-old female patient was admitted to our hospital with nephrotic syndrome and acute kidney injury. After admission, she presented with a skin rash and was serologically positive for syphilis. Kidney biopsy showed MN positive not only for immunoglobulin (Ig) G, but also for IgA and complement C1q. IgG subclass analysis revealed positivity for IgG1 and IgG3. Immunohistochemistry for glomerular NDNF was positive, and a diagnosis of syphilis-related MN was confirmed. Prior to treatment of the infection, her urinary protein decreased to achieve complete remission and her kidney function improved. Benzylpenicillin was administered, and no recurrence of nephrotic syndrome or kidney dysfunction was observed thereafter. This case illustrates the importance of considering syphilis infection when encountering a case of nephrotic syndrome with skin rash. In addition, urinalysis of syphilitic patients should be performed to avoid missing MN that may be in spontaneous remission. Further elucidation of the pathogenesis of NDNF-positive, syphilis-related MN in Japan is needed.