The IgM-related peripheral neuropathies (IgM-PN) are a group of chronic disorders characterized by the presence of monoclonal IgM that may be associated with one of several diseases affecting the peripheral nerves. In many cases, there is a monoclonal IgM associated with activity against neural targets, leading to progressive peripheral nerve demyelination. Neurological symptoms in this setting can also result from direct invasion of the peripheral or central nervous system by lymphoplasmacytic cells (neurolymphomatosis and Bing-Neel syndrome respectively) or via other mechanisms (for example AL amyloid deposition or cryoglobulinemic vasculitis). There is an expanding array of treatment options, but high-quality data are sparse. Diagnostic accuracy is important and needs collaboration between hematologists and neuromuscular specialists to determine the sequence and intensity of investigations. Appropriate causal attribution to the IgM disorder is essential to enable the correct therapeutic intervention. The aims of treatment intervention should be clear and realistic. Consistent and clinically meaningful measures are needed to capture treatment success. Despite therapeutic advances, many patients experience persistent disability, highlighting the need for further research.

Amyloidosis Research and Treatment Center IRCCS Policlinico San Matteo University of Pavia Pavia Italy

Assuta Ashdod University Hospital Faculty of Health Sciences Ben Gurion University of the Negev Jerusalem Israel

Bing Center for Waldenström's Macroglobulinemia Dana Farber Cancer Institute Harvard Medical School Boston MA

Centre for Neuromuscular Disease National Hospital for Neurology and Neurosurgery London UK

Centre for Waldenström Macroglobulinaemia and Related Conditions University College London Hospitals NHS Foundation Trust London UK

Colorado Blood Cancer Institute Sarah Cannon Research Institute Denver CO

Department of Clinical Therapeutics National and Kapodistrian University of Athens Athens Greece

Department of Haemato oncology University Hospital Ostrava and Faculty of Medicine University of Ostrava Ostrava Czech Republic

Department of Hematology Cancer Center Amsterdam LYMMCARE Amsterdam UMC University of Amsterdam Amsterdam The Netherlands

Department of Hematology Hadassah Medical Center Faculty of Medicine Hebrew University of Jerusalem Israel

Department of Hematology University Hospital of Amiens Amiens France

Department of Neurology Amsterdam UMC Amsterdam The Netherlands

Division of Hematology Fondazione iRCCS Policlinico San Matteo Italy

Hematology Unit IRCCS Istituto Scientifico Romagnolo per lo Studio dei Tumori Dino Amadori Meldola Italy

Institute of Experimental Cancer Research University Hospital Ulm Ulm Germany

Niguarda Cancer Center ASST Grande Ospedale Metropolitano Niguarda Milan Italy

Odette Cancer Centre Sunnybrook Health Sciences Centre Division of Medical Oncology and Hematology Faculty of Medicine University of Toronto Toronto Canada

Unit of Hematology Department of Biotechnology and Health Sciences University of Torino Torino Italy

University College London Hospitals NHS Foundation Trust London UK

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