Unknown humoral factors and some autoantibodies in sera from multifocal motor neuropathy (MMN) patients cause disruption of the blood–nerve barrier (BNB).

MMN is a pure motor neuropathy characterised by asymmetric distal dominant weakness, slowly progressive course and multifocal conduction blocks in nerve conduction studies.1 MMN is included in the list of the differential diagnosis of motor neurone disease because of the presence of atrophy and fasciculation in the affected limbs.

Patients with MMN frequently have elevated levels of immunoglobulin (Ig)M antibodies against ganglioside GM1 in sera.2 High-dose intravenous immunoglobulin and cyclophosphamide have been reported to be effective for …