Summarynating sensorimotor neuropathy. It should be considered as a clinical asymmetrical variant of chronic immune 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.

Amyotrophy in LSS

Rinsho Shinkeigaku. 2000 Nov;40(11):1126-9.[Lewis-Sumner syndrome presenting unilateral quadriceps amyotrophy as an initial symptom]

Fujiyama J,

Second Department of Internal Medicine, Fukui Medical University.

We report a 55-year-old man with a chief complaint of wasting and weakness of the left quadriceps muscle. At age 54, he noticed difficulty in running and weakness in the left thigh, which gradually progressed. On the first admission to our hospital, based on the nerve conduction studies (NCS), the muscle biopsy findings showing neurologenic changes, and no abnormality of spinal MRI, we diagnosed as unilateral quadriceps amyotrophy, which resulted from an atypical form of spinal progressive muscular atrophy. One year later, he showed the bilateral hand weakness, conduction blocks on the right median and ulnar nerves by NCS, and the presence of serum anti-GM 1 antibody. From these findings, Lewis-Sumner syndrome was diagnosed. The therapy of high-dose intravenous immunoglobulin moderately improved his symptoms.  It is important to consider Lewis-Sumner syndrome in the differential diagnosis of quadriceps amyotrophy.
Lewis-Sumner syndrome (LSS) is a dysimmune peripheral nerve disorder, characterized by a predominantly distal, asymmetric weakness mostly affecting the upper limbs with sensory impairment, and by the presence of multifocal persistent conduction blocks. . We report the clinical, biological and electrophysiological features, the course and the response to treatment in 23 LSS patients. The initial symptoms started in the distal part of an upper limb in 70% of patients. They were sensorimotor in 65% and purely sensory in 35% of patients. A cranial nerve involvement was observed in 26% of patients and a distal limb amyotrophy in 52%. The CSF protein level was normal in 67% of patients and mildly elevated in the remainder. None had serum anti-GM1 antibodies. There were multiple motor conduction blocks (average of 2.87/patient), predominantly located in the forearm, whereas demyelinating features outside the blocked nerves were rare. Abnormal distal sensory potentials were found in 87% of patients. The electrophysiological pattern suggests a very focal motor fibre demyelination sparing the nerve endings, whereas sensory fibre involvement was widespread. The course was chronic progressive in 71% of patients and relapsing-remitting in the others. During the follow-up study (median duration of 4 years), half of the patients progressed with a multifocal pattern and the distribution of the motor deficit remained similar to the initial presentation. The other patients showed a progression to the other limbs, suggesting a more diffuse process. Fifty-four percent of the patients treated with intravenous immunoglobulin showed an improvement, compared with 33% of the patients treated with oral steroids. Overall, 73% of patients had a positive response to immune-mediated therapy. LSS may be distinguished from MMN by the presence of sensory involvement, the absence of serum anti-GM1 antibodies and, in some cases, a positive response to steroids. continue to page-2 of LewisSummner