Journal of the Peripheral Nervous System 19:180–182 (2014) CASE REPORT Multifocal motor neuropathy with high titers of anti-MAG antibodies Claire Bridel 1 , Judit Horvath 1 , Mary Kurian 2 , André Truffert 1 , Andreas Steck 3 , and Patrice H. Lalive 1,4 1 Department of Clinical Neurosciences, Division of Neurology; 2 Department of Pediatrics, Geneva University Hospital, Geneva, Switzerland; 3 Department of Neurology, Basel University Hospital, Basel, Switzerland; and 4 Department of Genetics and Laboratory Medicine, Laboratory Medicine Service, Geneva University Hospital, Geneva, Switzerland Abstract Multifocal motor neuropathy (MMN) and anti-myelin-associated glycoprotein (anti-MAG)-associated neuropathy are clinically and electrophysiologically distinct entities. We describe a patient with characteristic features of both neuropathies, raising the possi- bility of an overlap syndrome. A 49-year-old patient reported a history of slowly progressive predominantly distal tetraparesis, with mild sensory deficits. Nerve conduction studies demonstrated persistent motor conduction blocks outside compression sites, typical of MMN. Laboratory findings revealed persistently high titers of anti-MAG immunoglobulin M (IgM) paraprotein in the context of a monoclonal gammapathy of unknown significance. Skin biopsy of distal lower limb revealed IgM positive terminal nerve perineurium deposits. This case suggests that the distinction between subtypes of chronic inflammatory neu- ropathies may not be as clear as initially thought, and that the pattern of pathogenicity of anti-MAG antibodies may vary. Key words: anti-MAG neuropathy, immune-mediated peripheral neuropathy, multifocal motor neuropathies Introduction Multifocal motor neuropathy (MMN) is a rare immune-mediated chronic motor neuropathy clinically characterized by asymmetrical muscle weakness in peripheral nerve territories. Persistent motor conduc- tion blocks outside compression sites are the elec- trophysiological hallmark. Anti-GM1 immunoglobulin M (IgM) antibodies have been described in associa- tion with MMN, but their role in pathogenesis is not established (Cats et al., 2010). Anti-myelin-associated glycoprotein (anti-MAG)-associated neuropathy has Address correspondence to: Dr. Claire Bridel, MD, PhD, Depart- ment of Clinical Neurosciences, Division of Neurology, Geneva Uni- versity Hospital and Faculty of Medicine, Gabrielle-Perret-Gentil 4, 1211 Geneva 14, Switzerland. Tel: +(41)22-372-83-18; Fax: +(41)22-372-83-32; E-mail: claire.bridel@hcuge.ch. been described as a chronic, length-dependent, sym- metrical, sensory–motor demyelinating neuropathy, also referred to as distal acquired demyelinating sym- metric (DADS) neuropathy. Monoclonal anti-MAG IgM paraprotein is detected in the context of an underlying MGUS (monoclonal gammapathy of undetermined significance), myeloma, Waldenström disease, or lymphoma. Several lines of evidence suggest a causal relationship between anti-MAG antibodies and neu- ropathy (Dalakas, 2010). Here, we describe a case illustrating a rare situation with simultaneous features of MMN and anti-MAG neuropathies. Case Report A 49-year-old female presented with a history of slowly progressive predominantly distal tetraparesis, without pain or sensory deficit. The first symptom she reported was progressive left foot drop 10years prior. © 2014 Peripheral Nerve Society 180