Case 6: Diagnosis and discussion:
Multifocal acquired demyelinating sensory and motor neuropathy (MADSAM, aka: Lewis Sumner syndrome).
CSF analysis: Glucose 61, protein: 62 (normal 15 – 45 mg/dL), WBC: 1/mL, Oligoclonal bands negative. Sural nerve biopsy (right column) showed axonal dropout but no clear evidence for demyelination (tease fiber preparation was not done). Lateral gastrocnemius muscle biopsy showed groups of atrophic, angular myofibers consistent with denervation (circled, see right column)
MADSAM is an asymmetrical variant of chronic inflammatory demyelinating polyneuropathy (CIDP) was initially described in 1982 1. Although the upper limbs are more commonly affected, the DTRs may be attenuated or absent throughout. Sensory impairment is typically patchy rather than stocking/gloves seen in typical CIDP, and neuropathic pain is not common. The electrophysiologic hallmark of MADSAM is motor conduction block (or partial conduction block) in at least one nerve in addition to sensory nerve conduction abnormalities (which can be diffusely abnormal or absent) 2,3. Asymmetrical involvement and sensory nerve abnormalities help differentiate MADSAM from CIDP and multifocal motor neuropathy (MMN) respectively. Conduction block is typically found in the median and ulnar nerves and often persists for months or even years. Other electrodiagnostic signs of demyelination (ie. slowed conduction velocity (in “demyelinating range”), temporal dispersion, prolonged distal latency and prolonged F-wave latency may also be present. CSF is normal or has mild elevation in protein (typically < 100 mg/dL) 3. Significant rise of anti-GM1 antibody is not characteristic for MADSAM, and is suggestive for MMN. Sensory nerve biopsy may show segmental demyelination, inflammatory infiltrates and loss of large myelinated fibers. The patients variably respond to IVIG infusions, steroids and other immunosuppressants 3,4.
References:
1. Lewis RA, Sumner AJ, Brown MJ, Asbury AK. Multifocal demyelinating neuropathy with persistent conduction block. Neurology. Sep 1982;32(9):958-964.
2. Saperstein DS, Amato AA, Wolfe GI, et al. Multifocal acquired demyelinating sensory and motor neuropathy: the Lewis-Sumner syndrome. Muscle Nerve. May 1999;22(5):560-566.
3. Rajabally YA, Chavada G. Lewis-sumner syndrome of pure upper-limb onset: diagnostic, prognostic, and therapeutic features. Muscle Nerve. Feb 2009;39(2):206-220.
4. Viala K, Renie L, Maisonobe T, et al. Follow-up study and response to treatment in 23 patients with Lewis-Sumner syndrome. Brain. Sep 2004;127(Pt 9):2010-2017.
