The Lewis- Sumner syndrome (LSS) is a dysimmune multifocal demyelinating sensorimotor neuropathy. It should be considered as a clinical asymmetrical variant of chronic inflammatory demyelinating polyneuropathy (CIDP). LSS is five times less frequent than CIDP whose prevalence is between 2 and 7/ 100,000. Patients with LSS usually present with an asymmetrical involvement of the upper limb with distal sensorimotor deficit in median or ulnar territories. A purely sensory onset with numbness and paresthesia or pain in median or ulnar territory is observed 30% of cases. A lower limb onset is present in 30% of patients with a distal and asymmetrical sensorimotor deficit. Amyotrophy and cranial nerve involvement may be observed in 50% and 20% of patients, respectively. LSS could mimick a nerve entrapment or a vasculitis. The course is progressive or remitting. Electrophysiological pattern associates a multifocal motor demyelination with conduction blocks mostly situated in the forearm. Contrarily to CIDP, other conduction anomalies (reduction of truncal motor nerve velocities, prolonged distal latencies or prolonged F waves) occur rarely outside the blocked nerve territory. Sensory conduction shows a multifocal sensory involvement. Sural nerve biopsy in LSS show elements consistent with a primary demyelination, indistinguishable from that seen in typical CIDP. However nervous biopsy is not necessary to establish the diagnosis. Serum anti-GM1 antibodies are negative and CSF protein content is usually normal or mildly elevated with a mean value of 0.7 g/l. LSS is characterized by a responsiveness to IVIg and steroids. For LSS patients, a treatment similar to that of CIDP, with a first line treatment with intravenous Ig (IVIg) (2g/kg/course), is recommended. Patients who do not respond after 2 or 3 courses should be switched to prednisone; a dose of 1mg/kg/day should be maintained for 4-6 weeks, then slowly tapered. Plasma exchanges are not recommended in LSS.
Last update: August 2003