Abstract:

A case of systemic lupus erythematosus (SLE) complicated with contactin-1 (CNTN1) antibody-positive autoimmune nodopathy (AN) is reported, with the aim of providing insights for the early recognition and precise management of this rare comorbidity. A 48-year-old woman was admitted with a history of limb numbness and weakness for more than one year and 8 months of bilateral lower-limb edema. More than one year prior, she presented to another hospital with distal limb weakness and numbness; cerebrospinal fluid examination revealed albuminocytologic dissociation, electromyography showed findings consistent with peripheral neuropathy. She was diagnosed with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and treated with intravenous immunoglobulin and methylprednisolone pulse therapy, but her symptoms continued to progress. Six months before admission, she developed bilateral leg edema; laboratory tests showed leukopenia (3×10⁹/L), proteinuria (urine protein/creatinine ratio 4.5 g/d) with hypoalbuminemia and hyperlipidemia, and serum anti-CNTN1 antibody positivity. Lumbar MRI revealed thickening of bilateral lumbosacral nerve roots, edema of the common peroneal nerve, and diffuse thickening of the brachial plexus. She was diagnosed with immune-mediated peripheral neuropathy and nephrotic syndrome, and treated with a single intravenous dose of rituximab (600 mg), followed by dexamethasone (15 mg/d for 5 days) transitioned to oral prednisone (60 mg/d, tapered). Limb weakness and numbness improved, leukocyte count normalized, but edema worsened. One week before the current admission, she developed alopecia; repeat testing showed worsened proteinuria (urine protein/creatinine 7.05 g/d), positive antinuclear antibody (1 ∶ 1000, cytoplasmic granular pattern), anti-double-stranded DNA (anti-dsDNA), anti-SSA, anti-Ro52 antibodies, and weakly positive anti-SSB antibody. SLE was suspected, and she was admitted to the Department of Rheumatology and Immunology, Peking University People' s Hospital. Repeat testing revealed elevated anti-dsDNA antibody (137 IU/mL), low C4, and seroconversion to negative for anti-CNTN1 antibody in both serum and CSF. Renal biopsy demonstrated atypical membranous nephropathy. Final diagnoses were SLE, CNTN1 antibody-positive AN, and lupus nephritis. She received intravenous methylprednisolone (40 mg/d) transitioned to oral prednisone (50 mg/d, tapered), hydroxychloroquine (0.2 g twice daily), and rituximab induction (500 mg weekly ×4) followed by 500 mg every 6 months as maintenance. During 2 years of follow-up, alopecia, limb weakness, and numbness improved, leukocyte count remained normal, and urine protein/creatinine decreased to 0.19 g/d. Autoimmune nodopathy, first formally recognized in July 2021, is a novel subtype of peripheral neuropathy. This is the third reported case worldwide of SLE coexisting with AN. The literature is reviewed, and possible shared pathogenic mechanisms, disease characteristics, and B-cell-depleting therapy as the cornerstone of management are discussed.

Key words: Systemic lupus erythematosus, Autoimmune nodopathy, Contactin 1