[Multifocal demyelinating polyneuropathy with persistent conduction block (Lewis-Sumner syndrome)].

Multifocal demyelinating neuropathy with persistent conduction block (Lewis-Sumner syndrome) is a variant of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), which often clinically simulates a motor neuron disease (MND). We report here three patients initially suspected to have MND, who later were diagnosed as a Lewis-Sumner syndrome. One of them showed a remarkable clinical improvement after immunoglobulin therapy. The definitive diagnosis of this syndrome rests upon nerve conduction studies, uncovering multiple sites of persistent conduction block. Technically, it is important to exclude insufficient stimulus which may lead to an erroneous impression of conduction block. Magnetic stimulation, as compared to electric current, elicited larger responses possibly because of deeper current penetration. We found this mode of stimulation useful especially in testing focal demyelination requiring full activation of a diseased nerve at a most proximal segment.