Peripheral and central presentation of neuropathic pain

Neuropathic pain is a pain originating within the peripheral or central nervous system and differs from nociceptive pain originated outside the nervous system. Pain due to disorders of the brain, however, originates also from abnormal interaction of cognitive and emotional pain processing brain areas. It might also arise from decreased activity of the hypothalamic and descending inhibitory pathways that are always at play both in physiological and pathological pain. To avoid the “grey zone” of such “functional pain states,” neurologists and neurophysiologists have confined the definition of neuropathic pain to “pain caused by injury or disease of the somatosensory system.” The present chapter adheres to this restrictive definition; however, it also describes painful conditions caused by strictly neurological disease such as spinal cord injury, restless legs syndrome, Parkinson’s disease and epilepsy that put forward the relevance of the descending inhibitory system into the generation of central neuropathic pain.