Acquired disorder of peripheral nerves, affecting motor and sensory fibers of the limbs, reaching the nadir of deficits 8 weeks or later from onset, and exhibiting a relapsing-remitting or progressive course. Diagnostic features include neurophysiologic evidence of demyelinating neuropathy, elevation of CSF protein level without pleocytosis, and neuropathologic findings of peripheral segmentary demyelination with perineural and endoneural inflammatory infiltrates. Pure motor or pure sensory variants are very rare and may represent an intermediate stage of the classic disease. Progressive chronic inflammatory demyelinating polyradiculoneuropathy is another variant, which shows a steadily worsening course without remission. Chronic inflammatory demyelinating polyradiculoneuropathy with severe axonal loss is a rare variant characterized by a relapsing-remitting course with evidence of axonal damage. Chronic inflammatory demyelinating polyradiculoneuropathy with monoclonal gammopathy of undetermined significance affects a subgroup of patients with the neuropathy and a monoclonal gammopathy usually of IgG or IgA type.