Nerves and nephrons – Think about contactin-1 antibodies

<h3></h3> A 65-year-old man was admitted with a one-month history of tingling hands and feet, reduced hand strength and worsening balance with falls. Examination revealed wasting, weakness, sensory loss, areflexia, upper limb action tremor, and a broad-based gait. Key investigations: Neurophysiology: Symmetrical sensorimotor demyelinating polyneuropathy CSF: Few white cells, persistently raised protein (initially 3.78g/L), matched oligoclonal bands, normal glucose/cytology/flow cytometry MRI: Nerve root and leptomeningeal enhancement in the spine Bloods: Two IgM–kappa paraproteins Bone marrow biopsy: Low level lymphoplasmocytic lymphoma Nerve biopsy: Depletion of large myelinated fibres Serum albumin dropped to 15 g/L, nephrotic range proteinuria detected, raised urinary protein:creatinine ratio Renal biopsy: Membranous nephropathy, PLA2R staining negative The initial diagnoses considered were chronic inflammatory demyelinating neuropathy (CIDP) or Bing-Neel syndrome. Initial treatment was with intravenous immunoglobulin and steroids. Rituximab was subsequently started as it was considered an appropriate treatment for both CIDP and lymphoma. After identification of membranous nephropathy, paranodal antibody testing identified positive Contactin-1 (CNTN1) antibodies. The patient made an excellent neurological and renal recovery over 6 months. Repeat CNTN1 antibodies at 3 months were negative. In summary, the combination of CIDP-like presentation and nephrotic syndrome should raise the possibility of paranodal antibodies, particularly CNTN1.