Classic chronic inflammatory demyelinating polyneuropathy (CIDP) is characterized by the occurrence of symmetrical weakness in both proximal and distal muscles that progressively increases for more than two months (setting this condition apart from the Guillain–Barré syndrome, which is self-limited). The condition is associated with impaired sensation, absent or diminished tendon reflexes, an elevated cerebrospinal fluid protein level, demyelinating nerve-conduction studies, and signs of demyelination in nerve-biopsy specimens. The course can be relapsing or chronic and progressive, the former being much more common in young adults.
These criteria are applied by testing the median, ulnar (stimulated below the elbow), peroneal (stimulated below the fibular head), and tibial nerves on one side of the body. During testing, limb temperature should be no less than 33°C at the palm and no less than 30°C at the external malleolus.