Asymmetric Acquired Demyelinating Polyneuropathies: MMN and MADSAM

More than a half a century after Austin's initial description of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the clinical spectrum of chronic acquired demyelinating polyneuropathies has expanded. Currently there are a number of entities that can be put under the heading of chronic acquired demyelinating neuropathy (CADP) based on differing clinical presentations. In this scheme, CIDP is used only to refer to patients with demyelinating neuropathies and generalized symmetric weakness. In contrast, multifocal motor neuropathy (MMN) and multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) fall into the category of asymmetrical, multifocal forms of CADP. These are distinguished from each other only by the presence of sensory involvement. In our opinion, there are pragmatic reasons for splitting these clinical presentations into distinct entities. Although each of these clinical subtypes shares some basic similarities, there are important differences. MMN is usually considered resistant to corticosteroid therapy and the first line agent in this disorder is intravenous immunoglobulin (IVIg). MADSAM neuropathy can be responsive to prednisone or IVIg, and has a profile more analogous to classic CIDP with regards to its laboratory features and treatment response.