Articles: neuralgia.
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Neuropathic pain is defined as "pain initiated or caused by a primary lesion or dysfunction in the nervous system". Neuropathic orofacial pain has previously been known as "atypical odontalgia" (AO) and "phantom tooth pain". The patient afflicted with neuropathic oral/orofacial pain may present to the dentist with a persistent, severe pain, yet there are no clearly identifiable clinical or radiographic abnormalities. ⋯ The aberrant developmental neurobiology leading to this pain state is complex. Neuropathic pain serves no protective function, in contrast to physiological pain that warns of noxious stimuli likely to result in tissue damage. The relevant clinical features of neuropathic pain include: (i) precipitating factors such as trauma or disease (infection), and often a delay in onset after initial injury (days-months), (ii) typical complaints such as dysaesthesias (abnormal unpleasant sensations), pain that may include burning, and paroxysmal, lancinating or sharp qualities, and pain in an area of sensory deficit, (iii) on physical examination there may be hyperalgesia, allodynia and sympathetic hyperfunction, and (iv) the pathophysiology includes deafferentation, nerve sprouting, neuroma formation and sympathetic efferent activity.
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Experimental neurology · Apr 2000
Nerve injury-induced mechanical but not thermal hyperalgesia is attenuated in neurokinin-1 receptor knockout mice.
Mice lacking the gene encoding for substance P and neurokinin A, or the NK-1 receptor, exhibit alterations in behavior to various acute nociceptive stimuli. However, behavioral responses of NK-1 mutant animals have not been well characterized in models of chronic pain. We studied the behavioral responses of NK-1 knockout and wild-type control mice to thermal and mechanical stimuli before and after inducing chronic neuropathic pain by unilateral ligation of the L5 spinal nerve. ⋯ Similarly, the increase in withdrawal frequency to the cooling stimuli following the nerve injury was not different in the NK-1 knockout and wild-type mice. Mechanical hyperalgesia in the wild-type mice was not reversed by systemic administration of phentolamine, suggesting that the pain is not sympathetically maintained. The results indicate that NK-1 receptors contribute to the development of mechanical, but not thermal, hyperalgesia in neuropathic pain.
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Electrical stimulation of selected peripheral nerves for treatment of intractable pain has been used inconsistently over the past 30 years due to difficulties in clarifying appropriate indications, utilizing approved device technology, and standardizing the surgical techniques. Circumferential electrodes treating mononeuropathies have given way to paddle electrode techniques and, most recently, the application of percutaneous wire electrode methods will allow for minimally invasive peripheral nerve stimulation for certain intractable CRPS and other painful monoeuropathies.
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Reactivation of varicella-zoster virus causes herpes zoster, which accompanies severe pain in most patients. Treatment of pain is mandatory in herpes zoster. Pain caused by herpes zoster is classified as acute herpetic pain and postherpetic neuralgia. ⋯ Treatment for acute herpetic pain includes antiviral drugs, non-steroidal anti-inflammatory drugs, opioids, and sympathetic nerve blockade. Postherpetic neuralgia is a neuropathic pain and requires antidepressants, anticonvulsants, and anti-arrhythmic drugs to relieve the pain. Topical application of capsaicin and local anesthetics may benefit some patients with postherpetic neuralgia.
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Neuropathic pain is often resistant to opioids, so other medication classes, such as tricyclic antidepressants, anticonvulsants, and local anesthetics, are often used. Central sensitization, or pain 'wind-up', may perpetuate chronic neuropathic pain even when ongoing peripheral sensory input is absent. Wind-up is thought to cause allodynia, hyperalgesia, and hyperpathia. ⋯ No significant side effects were reported. Ketamine Gel may provide clinicians with a new option in the battle against chronic neuropathic pain. Until further information is available and larger trials can be conducted, we can only recommend this type of therapy for refractory cases in which all primary and secondary options have been exhausted.