Chronic Inflammatory Demyelinating Polyneuropathy and Concurrent Membranous Nephropathy Associated With Anti-Contactin-1 Autoantibodies: A Rare Case Report With a Review of the Literature.

Membranous nephropathy (MN) stands as the most common origin of nephrotic syndrome in adults. Nevertheless, it is quite unusual for individuals to simultaneously manifest both chronic inflammatory demyelinating polyneuropathy (CIDP) and MN along with the presence of positive anti-contactin-1 (CNTN1) antibodies. Only a limited number of case reports in scientific literature have described such occurrences to date. Typically, CIDP patients exhibit symptoms characterized by proximal and distal weakness and sensory abnormalities. We present a rare case of CIDP and MN with positive anti-CNTN1 antibodies in our setting and describe our experience in management of the condition. Moreover, noticing the rarity of this condition, we performed an analysis of the existing literature to comprehensively analyze the diagnostic, management, and clinical outcomes for this condition. Our patient, a 45-year-old male, had a pre-existing diagnosis of CIDP at the age of 43, in March 2015. Approximately 18 months later, in September 2016, this patient presented with nephrotic syndrome, leading to a subsequent diagnosis of stage 2 MN. The diagnosis was confirmed through renal biopsy results, which revealed thickening of the glomerular basement membrane and immunoglobulin G4 (IgG4) deposits. However, the patient tested negative for anti-phospholipase 2 antibody. Further diagnostic evaluation was performed, and anti-CNTN1 antibodies were detected. The patient was successfully treated with cyclosporine therapy 150 mg twice a day and prednisone, and no complications were noted; however, partial relapse on remission of cyclosporine was observed. Based on our case analysis and comprehensive review of existing literature, it is evident that there are similarities between CIDP with MN and positive anti-CNTN1 antibodies, but they are not identical conditions. Therefore, we propose the assessment of anti-CNTN1 antibodies as part of the evaluation for patients who exhibit both CIDP and MN symptoms. Anti-CNTN 1 antibody may be a novel diagnostic test in this condition and may allow determination of therapeutic response soon; however, this needs to be backed up with evidence from research studies in the future.