--to have conduction block with other conditions than multifocal motor neuropathy; in motor neuropathy the conduction block is normally due to a focal demyelination caused by an autoimmune situation, but anything that demyelinates an area of nerve, or breaks enough of the axon, can cause it--most notably local swelling/ischemia due to traumatic injury.

I'd be willing to wager, given how infrequently diagnosed multifocal motor neuropathy is, most instances of conduction block on EMG are due to injury--either sudden or long term from compressive forces in the spine from disc herniation or osteophytic overgrowth.