In the mid-1980s, Pestronk reported the first cases of multifocal motor neuropathy to be associated with serum anti-monosialoganglioside (GM1) IgM antibodies.1 The potential importance of an easily measurable antibody as a biomarker for this diagnostically challenging but treatable neurological disorder was rapidly recognised. Subsequently, an extensive literature has emerged on the usefulness of anti-GM1 antibody testing in clinical practice and on its relationship to multifocal motor neuropathy (MMN) pathogenesis. The conventional ELISA sensitivity is currently considered to be around 50%; perhaps as a result of this rather poor performance, many clinicians pay scant notice to a positive or negative result, preferring to use clinical judgment and electrophysiological assessment as the …