--the distinction between mononeuritis (or mononeuropathy) multiplex and polyneuropathy is not that important--it is one of nomenclature, not reality.

Mononeuropathy was coined for those who have damage to one particular nerve tract, and monneuropathy multiplex for damage to several, particular nerve tracts. But as things get more systemic, the distinction between polyneuropathy and mononeuropathy multiplex blurs into nonexistence. There's really no distinction between a condition that affects many nerve tracts and one that affects many nerves, unless some have to make it for insurance reimbursement (and I think the categories are more archaic than useful).

It's more important to characterize neuropathies by type of fiber affected--small vs. large vs. autonomic--by type of damage--demyelinating vs. axonal-- or by cause, if one can be found.