--is turning more and more into a clinical diagnosis. True enough, a nerve biopsy (rather than a skin biopsy) can sometimes clearly show the trophic changes associated with a relapsing-remitting demyelinating inflammatory neuropathy, but plenty of people have been given the diagnosis without one, based on blood/spinal fluid work-ups catching protein/antibodies of one sort of another, response to IVIg, or just plain EMG/NCV results.

Truth be told, CIDP is a rather broad and catch-all term. Many neuros use it to refer to any long-term demyelinating neuropathy in which there is evidence of inflammatory process. But there are many other conditions that can directly cause a chronic demyelination, especially toxic or hereditary ones:

http://www.neuro.wustl.edu/NEUROMUSC...dem.html#table

http://www.neuro.wustl.edu/NEUROMUSC...er/myelin.html

All too often, if the doctors are not being thorough in their investigations, the evidence of demyelination leads them to designate CIDP without looking for the patterns that may indicate how the process is occurring, and where along the myelin, which might point to a more specific disease. The classic presentation of CIDP involves macrophage-mediated stripping of myelin (to greater or lesser degree) all along the axon, but irregularly spaced damage or involvement of the Schwann cells might suggest something that is more specific.

As cycleops notes, the definitions of these conditions are very fluid as medical and genetic research goes forward, and we are likely to see redefinitions/reclassificiations in the future.