Introduction

The early diagnosis of amyotrophic lateral sclerosis (ALS) is often difficult as not all patients meet clinical and electrophysiological criteria.1 Additionally a small per cent of patients have a divergent diagnosis, most commonly multifocal motor neuropathy (MMN) or motor-predominant multifocal acquired demyelinating sensory and motor neuropathy (MADSAM).2 Although motor conduction blocks distinguish MMN and MADSAM from ALS, it is often difficult to find these conduction abnormalities when present at the roots or plexus. Currently biomarkers to assist in the diagnosis of ALS versus MMN and MADSAM are inadequate. Specifically, GM1 (ganglioside monosialo-asialo) autoantibodies can be present in all these disorders, although typically of lower values in ALS. Recently, IgM-gammopathy was suggested to be more common in MMN (7%) compared with healthy (2%) and ALS (1%) controls.3 If true, IgM-gammopathy may forebode for an immune treatment refractory disorder as described in other IgM-gammopathy neuropathies.4

Herein, we address: (1) the occurrence of an IgM-gammopathy in MMN and MADSAM compared with ALS and (2) evaluate the immune treatment response of MMN and MADSAM IgM-monoclonal-gammopathy.