Pathophysiology of Neuropathic Pain: a Systemic Review

Neuropathic pain is considered as an inappropriate response caused by a lesion or dysfunction in the PNS or CNS). Neuropathic pain can manifest itself as either without a stimulus (stimulus-independent pain) and/ or as pain hypersensitivity elicited after a stimulus (stimulus-evoked pain). Stimulusindependent pain includes symptoms described by the patient such as (a) continuous, burning pain (b) intermittent shooting, lancinating pain (c) some dysaesthesias. Conversely, stimulus-evoked pain describes signs the physician induces after mechanical, thermal or chemical stimulation, and usually involves hyperalgesia or allodynia. The mechanism(s) underlying neuropathic pain are not completely understood but are considered to be complex, multifactorial and to evolve over time. Neuropathic pain can be trauma (surgical and non-surgical), accidents, and exposure to toxins, infection, viruses, metabolic diseases, nutritional deficiency, ischemia, and stroke. Current research studies indicate that both peripheral and central mechanisms have been involved in pathogenesis of neuropathic pain. INTRODUCTION: On the basis of pathological condition, pain may be classified as nociceptive pain and NP. Nociceptive pain is an appropriate physiological response to a painful stimulus and various modulatory mechanisms are involved, which can usually be controlled with standard analgesics. Conversely, NP occurs as a consequence of primary lesion or dysfunction in the nervous system either the central nervous (CNS) or the peripheral nervous system (PNS). NP is considered as an inappropriate response caused by a lesion or dysfunction in the PNS or CNS. NP can manifest itself as either without a stimulus (stimulusindependent pain) and/ or as pain hypersensitivity elicited after a stimulus (stimulus-evoked pain). Stimulus-independent pain includes symptoms described by the patient such as (a) continuous, burning pain (b) intermittent shooting, lancinating pain (c) some dysaesthesias. Conversely, stimulus-evoked pain describes signs the physician induces after mechanical, thermal or chemical stimulation, and usually involves hyperalgesia or allodynia. Normally, non-noxious stimuli such as brushing against clothing, or a puff of air might now elicit pain (tactile allodynia), however stimuli with sharp features, such as a stiff bristle, or the rough surface of sandpaper, will elicit considerable pain that outlasts the stimulus (mechanical hyperalgesia). In addition to chronic, spontaneous NP, the mechanical dysaesthesia of allodynia and hyperesthesia are most troublesome because of our daily need to interact with objects in our environment.