Neurophysiological assessment of painful neuropathies.

Nociceptive inputs reach the CNS by means of small myelinated and unmyelinated fibers. Owing to this, conventional nerve conduction studies and electromyography are less likely to demonstrate abnormalities in neuropathies affecting nociceptive fibers than in those involving large myelinated fibers. Therefore, to characterize painful neuropathies, clinicians evaluate the features of the lesion that cause pain rather than the feeling of pain itself. Clinical neurophysiological assessment of painful neuropathies still relies on conventional nerve conduction studies but slightly more sophisticated techniques bring more specific information. These are the nociceptive-evoked potentials, microneurography or autonomic nervous system functional tests. Neurophysiological techniques can also add information to quantitative sensory testing by recording autonomic responses such as the sudomotor skin response or the voluntary reaction. Functional magnetic resonance should also be considered as a neurophysiological technique, which allows for mapping the areas of the brain involved in nociceptive sensation and pain control.