--refers to antibodies to myelin associated glycoprotein (that's where the acronym comes from), which is one of the basic building blocks of the myelin sheath in both the central the peripheral systems. If one has antibodies, one tends to have a demyelinating neuropathy that has both sensory and motor manifestations, and these can be quite debilitating, as the antibody titer tends to get in the way of the nerves' attempts to remyelinate.

Many people with such a neuropathy also have antibodies to SGPG--sulfated glucuronyl paragloboside, and--here's an area of greater concern--serum M-proteins (monoclonal antibodies) of the IgM class. These are often associated not only with neuropathies in their own right, but with certain blood cancers, and a thorough hematological work-up is recommended.

See:

http://www.neuro.wustl.edu/neuromusc...imdem.html#mag

There are some moderatly effective treatments, but these usually involve the heavy immune suppresants that often are used for blood cancers, such as Rituxan and Cyclophosphamide. Plasma exchange may also prove useful to lower antibody titers.