[Diagnosis of neuropathic pain]

Abstract

Pain usually is the consequence of tissue damage that is signalled to the brain via the nociceptive system (nociceptive pain). Damage to the nociceptive system - in addition to causing sensory deficit - may paradoxically also induce a chronic pain state (neuropathic pain). Diagnostic workup of patients with neuropathic pain follows the usual procedure of Neurology, i. e. the aim is to identify the location of neural damage and the underlying disorder, so that a mechanism-oriented treatment may be initiated. Medical history - supported by specific questionnaires and a pain drawing by the patient - provides the basis for diagnosis. In the course of the physical examination, the sensory exam including careful documentation of the spatial extent of positive and negative signs is the most important part, since neuropathic pain is due to damage to the somatosensory system. Techniques for the objective documentation of sensory signs have been developed (e. g. by the DFNS), but their broad availability is still in teh process of being implemented. Thus, laboratory exams main serve the purpose of identifying the underlying etiology. Symptomatic treatment of neuropathic pain is relatively uniform, independent of etiologies (e. g. traumatic, metabolic, inflammatory), but differs from that of nociceptive pain. Typical analgesics have little efficacy in neuropathic pain - except for opioids. Major pharmacological treatment options include anticonvulsants (Ca-channel modulators, Na-channel blockers), antidepressants (noradrenaline reuptake inhibitors) and topicals (lidocaine, capsaicin). These medications exert specific molecular pharmacological effects against the pathophysiological mechanisms of neuropathic pain.