Neuropathic pain syndromes

The amide local anaesthetic lidocaine may also be used as an antianhythmic for ventricular tachycardia and exra-systoles after injection into the blood circulation. Drugs with high lipid solubility such as bupivacaine cannot be used for these purposes because their prolonged binding to the channel may induce dysrhythmias or asystolic heart failure [3]. Systemically applied lidocaine has also been used successfully in some cases of neuropathic pain syndromes [4]. Here, electrical activity in the peripheral nervous system is reduced by used-dependent but incomplete sodium channel blockade. 

In the peripheral nervous system (PNS), HIV-1 infection and its treatment using HAART are associated with the development of neuropathic pain syndromes characterized by severe lancinating pain as well as parathesias and burning pain in the extremities. Damage to peripheral nerves has been associated with these syndromes. HIV-1-associated polyneuropathy has become the most common neurological complication of HIV-1 infection (Pardo et al. 2001). More than half of individuals with... 

Association of Pain, neuropathic pain is defined as pain initiated or caused by a primary lesion, dysfunction in the nervous system". Neuropathy can be divided broadly into peripheral and central neuropathic pain, depending on whether the primary lesion or dysfunction is situated in the peripheral or central nervous system. In the periphery, neuropathic pain can result from disease or inflammatory states that affect peripheral nerves (e.g. diabetes mellitus, herpes zoster, HIV) or alternatively due to neuroma formation (amputation, nerve transection), nerve compression (e.g. tumours, entrapment) or other injuries (e.g. nerve crush, trauma). Central pain syndromes, on the other hand, result from alterations in different regions of the brain or the spinal cord. Examples include tumour or trauma affecting particular CNS structures (e.g. brainstem and thalamus) or spinal cord injury. Both the symptoms and origins of neuropathic pain are extremely diverse. Due to this variability, neuropathic pain syndromes are often difficult to treat. Some of the clinical symptoms associated with this condition include spontaneous pain, tactile allodynia (touch-evoked pain), hyperalgesia (enhanced responses to a painful stimulus) and sensory deficits. 

Since local anesthetics have membrane-stabilizing effects, both parenteral (eg, intravenous lidocaine) and oral (eg, mexiletine, tocainide) formulations of local anesthetics have been used to treat patients with neuropathic pain syndromes because these syndromes are thought to involve uncontrolled, rapid, sensory fiber firing. Systemic local anesthetic drugs are commonly used as adjuvants to the combination of a tricyclic antidepressant (eg, amitriptyline) and an anticonvulsant (eg, carbamazepine) in chronic pain patients who fail to respond to the combination of antidepressant and anticonvulsant. 

Mexilitine has analgesic properties in several neuropathic pain syndromes and is an alternative agent for treatment of patients who fail to respond to tricyclic antidepressants or who cannot tolerate them... 

Tremont-Lukats, I. W., Megeff, C., Backonja, M. M. Anticonvulsants for neuropathic pain syndromes mechanisms of action and place in therapy, Drugs 2000, 60, 1029-1059. 

Furthermore, lack of Y1 receptor or antagonism at this receptor inhibited the antinociceptive potency of NPY at the spinal level. These data suggest that the Y1-receptor system exerts tonic inhibitory control and it mediates the antiallodynic effects of NPY during inflammatory and neuropathic pain syndromes. 

May reduce pain in other neuropathic pain syndromes within a few weeks... 

One of the few agents that enhances slow-wave delta sleep, which may be helpful in chronic neuropathic pain syndromes... 

Schwartzman, R.J. Malcki, H. Post injury neuropathic pain syndromes. Med. Clin. North Am. 1999, 83 (3), 597-626. 

Neuropathic pain is distinctly different from nociceptive pain. It is pain sustained by abnormal processing of sensory input by the peripheral or CNS. A large number of neuropathic pain syndromes exist (Fig. 58-2), and they are often difficult to treat. In addition, the pain reported often is not evident by examining physical findings. 

Motor cortex stimulation is reserved for the treatment of complex central and neuropathic pain syndromes that have proven refractory to medical treatment, including post-stroke pain, deafferentation pain, and some neuropathic pain states of peripheral origin. 

Jensen TS, Hansson PT. Chapter 34. Classification of neuropathic pain syndromes based on symptoms and signs. Handb Clin Neurol 2006 81 517-526. 

In addition to maintenance treatment for opioid-dependent individuals, methadone is very useful as a long-acting analgesic, particularly for neuropathic pain syndromes that accompany malignancy, and chronic non-malignancy pain, or where the efficacy and side effects of commonly employed opioids are unacceptable. Pain which is poorly responsive to morphine or other opioid agonists should be identified quickly so that futile dose escalation and intolerability can be avoided. 

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