--a demyelinating peripheral neuropathy, in which the primary deterioration is to the myelin sheathing that covers the larger nerves that control motor functions and the sensory modalities of vibration, mechanical touch, and position sense.

There is myelin sheathing in the brain and spinal cord (central nervous system) and that too can deteriorate in various conditions--notably multiple sclerosis--but the structure of that myelin is somewhat different from that of the myelin covering peripheral nerves, and apparently is attacked by different antibodies in autoimmune situations.

Small-fiber neuropathy results from attack on the much thinner, lightly myelinated and unmyelinated nerve fibers that subsume the sensations of pain and temperature, and also many autonomic functions. This neuropathy is by definition predominantly axonal--that is, caused by damage to the nerve fiber itself.