Aetiology of neuropathic pain

1959 Neuropathic pain is a pathological pain The capacity to experience pain has a protective role: it warns us of imminent or actual tissue damage and elicits coordinated reflex and behavioural responses to keep such damage to a minimum. If tissue damage is unavoidable, a set of excitability changes in the peripheral and central nervous system establish a profound but reversible pain hypersensitivity in the inflamed and surrounding tissue. This process assists wound repair because any contact w i t h the damaged part is avoided until healing has occurred. By contrast, persistent pain syndromes offer no biological advantage and cause suffering and distress. Such maladaptive pain typically results from damage to the nervous system—the peripheral nerve, the dorsal root ganglion or dorsal root, or the central nervous system—and is known as neuropathic pain. Such syndromes comprise a complex combination of negative symptoms or sensory deficits, such as partial or complete loss of sensation, and positive symptoms that include dysaethesia, paraesthesia, and pain. Apart from trigeminal neuralgia, which responds well to c a r b a m a z e p i n e , pharmacotherapy for neuropathic pain has been disappointing. Patients with neuropathic pain do not respond to non-steroidal anti-inflammatory drugs and resistance or insensitivity to opiates is common. Patients are usually treated empirically with tricyclic or serotonin and norepinephrine uptake inhibitors, antidepressants, and anticonvulsants that all have limited efficacy and undesirable s i d e e f f e c t s . Neurosurgical lesions have a negligible role and functional neurosurgery, including dorsal column or brain stimulation, is controversial, although transcutaneous nerve stimulation may provide some relief. Local anaesthetic blocks targeted at trigger points, peripheral nerves, plexi, dorsal roots, and the sympathetic nervous system have useful but short-lived effects; longer lasting blocks by phenol injection or cryotherapy risk irreversible functional impairment and have not been tested in placebo-controlled trials. Chronic epidural administration of drugs such as clonidine, steroids, opioids, or midazolam is invasive, has side-effects, and the efficacy of these drugs has not been adequately assessed. There is no treatment to prevent the development of neuropathic pain, nor to adequately, predictably, and