In 1982, Lewis and colleagues 7 described an unusual neuropathy which could best be characterized as a demyelinating mononeuropathy multiplex. Patients developed slowly evolving neurological deficits in a restricted distribution, within the territory of individual peripheral nerves. In all five patients, these deficits involved both sensory and motor functions, although the latter predominated. The disorder was very chronic, with symptoms evolving over more than 20 years in one patient. Deficits were most prominent in the upper extremities. The authors regarded this neuropathy as a variant of chronic inflammatory demyelinating neuropathy (CIDP); the principal feature that set it apart from typical CIDP was the nature and distribution of the electrophysiological findings. In each patient there was severe motor conduction block that was restricted to quite short segments of affected nerves; motor conduction in intervening segments was relatively preserved. Furthermore, the conduction block was persistent, remaining unchanged in severity and distribution for periods as long as 3 years. Sensory conduction studies were abnormal in all patients but, in keeping with the clinical picture, the abnormalities were relatively minor in most. Sensory nerve pathology was most consistent with primary demyelination with some associated axon loss and was altogether indistinguishable from that seen in typical CIDP. In two patients, the cerebrospinal fluid (CSF) protein was mildly elevated, but both had optic neuritis as well as neuropathy. Two patients were treated with prednisone and improved. This neuropathy has become known as the Lewis-Sumner syndrome.
In 1988, Parry and Clarke 9 described five very similar patients whose clinical picture differed