Beyond Chronic Inflammatory Demyelinating Polyradiculoneuropathy: Anti-Contactin-1 Autoimmune Nodopathy Unmasked by Proteinuria

Background/Objectives: Autoimmune nodopathies are a distinct subgroup of immune-mediated peripheral neuropathies caused by antibodies targeting nodal and paranodal proteins, including contactin-1 (CNTN1). These disorders are frequently misclassified as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), despite fundamental differences in pathophysiology, clinical course, and treatment response. Growing evidence indicates that systemic manifestations, such as proteinuria, may represent relevant diagnostic red flags. We report a case of anti-CNTN1 autoimmune nodopathy with renal involvement and long-term follow-up after rituximab therapy. Methods: We describe the longitudinal clinical, electrophysiological, laboratory, and therapeutic features of a patient presenting with an acute/subacute sensory ataxic neuropathy evolving into a chronic immune-mediated disorder. Serial nerve conduction studies were performed during multiple hospital admissions and follow-up visits. Autoantibody testing for nodal/paranodal antigens was undertaken, and systemic biomarkers were monitored over time. Results: The patient initially exhibited a robust response to intravenous immunoglobulin (IVIg), consistent with an acute inflammatory neuropathy. Subsequent relapse was characterized by cranial nerve involvement, worsening sensory ataxia, peripheral edema, albuminocytologic dissociation on cerebrospinal fluid analysis, proteinuria, and an inverted albumin/gamma globulin ratio, redirecting the diagnostic hypothesis toward CIDP. The detection of anti-CNTN1 antibodies ultimately established the diagnosis of autoimmune nodopathy. Owing to poor durability of IVIg, rituximab was initiated, resulting in sustained clinical improvement and near-complete recovery of motor and sensory nerve conduction parameters at one-year follow-up (November 2025). Conclusions: This case emphasizes the diagnostic relevance of extraneurological biomarkers, including proteinuria and peripheral edema, in autoimmune nodopathies and supports early nodal/paranodal antibody testing in atypical demyelinating neuropathies. Prompt B-cell-directed therapy may enable functional recovery of nodal integrity and improve long-term outcomes. Further studies are needed to clarify potential immunological triggers, including anti-IL-23 therapies, in the pathogenesis of anti-CNTN1 autoimmune nodopathy.