Case 6: Nerve conduction study and EMG

The nerve conduction study shows demyelinating range slowing and conduction blocks in the R.median and bilateral ulnar nerves, consistent with segmental demyelination. Although the tibial CMAP is within normal range, its F wave latency is significantly prolonged, pointing to demyelination in the proximal section. Note the significant asymmetry of the abnormalities of SNAPs, absent left radial, and normal sural SNAPs, which denote a multifocal neuropathy with demyelinating features, that is predominantly affecting the upper limbs. Needle study showed mild denervation in the gastrocnemius.  

What is the differential diagnosis? the further diagnostic steps? (click here)