Autoimmune nodopathy associated with Sjögren's disease and nephrotic syndrome: a case report and literature review.

Background: Anti-contactin-1 (CNTN1) antibody-positive autoimmune nodopathy (AN) is frequently reported in association with membranous nephropathy; however, the co-occurrence with both Sjögren's disease and nephrotic syndrome represents an exceptionally rare comorbid phenotype. In this study, we explored the potential immunological links underlying this comorbidity and, in conjunction with a literature review, sought to identify diagnostic clues for AN. Case presentation: We report the case of a 45-year-old woman who presented with progressive numbness and weakness of all four limbs for 5 months, accompanied by xerostomia and bilateral lower limb edema. Nerve conduction studies demonstrated demyelinating features, and cerebrospinal fluid analysis revealed albuminocytologic dissociation. Serum testing was positive for anti-CNTN1 antibodies (titer 1:1000), along with nephrotic-range proteinuria (4.66 g/24 h) and positivity for anti-SSA52, anti-SSA60, and anti-SSB antibodies. The patient was ultimately diagnosed with anti-CNTN1 antibody-positive AN coexisting with Sjögren's disease and nephrotic syndrome. Following intravenous methylprednisolone therapy, her neurological symptoms improved significantly. Conclusion: This case highlights that, within an immune context characterized by B-cell hyperactivation, anti-CNTN1 antibodies may mediate immune injury to both the peripheral nerves and kidneys by targeting shared antigens. Clinicians should recognize key diagnostic clues, including massive proteinuria, postural tremor, and poor response to intravenous immunoglobulin, to facilitate early identification of AN.