Management of Neuropathic Pain

Management of Neuropathic Pain

Elon Eisenberg
Published: European Neurological Disease 2006 Issue 2
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Definition and Scope of Neuropathic Pain

According to recent estimations 1.5–8% of the general population suffer from neuropathic pain.1,2 Neuropathic pain may result from a large variety of insults to the peripheral or central somatosensory nervous system, including traumatic, inflammatory, degenerative, ischemic, metabolic and neoplastic disorders. Common examples of peripheral neuropathic pain include lumbar or cervical radiculopathy, diabetic polyneuropathy (DPN) and post-herpetic neuralgia (PHN). Neuropathic pain of central origin includes central post-stroke pain, pain in multiple sclerosis and post-spinal cord injury pain. Neuropathic pain is characterised by continuous or intermittent pain, typically described as burning, aching or shooting in quality, and is often associated with abnormal sensitivity of the painful site (i.e. hypersensitivity to normally innocuous stimuli such as running water or cold air, a phenomenon known as allodynia).3 Neuropathic pain has negative effects on multiple domains of life and therefore the quality of life of patients with neuropathic pain is comparable to that experienced by patients suffering from cancer or chronic heart failure. This is further aggravated by the fact that neuropathic pain is often undiagnosed and undertreated.4

Management of Neuropathic Pain
The management of neuropathic pain involves the use of a wide variety of agents including antidepressants, anticonvulsants, opioids, topical agents and others. Yet, even with the current generation of these drugs, effective pain relief is achieved in less than half of patients with chronic neuropathic pain.5,6 In patients with refractory neuropathic pain, administration of combination therapy of two or more agents with synergistic mechanisms,7 or implantation of neuromodulation devices, such as spinal cord stimulators or intrathecal drug delivery pumps, can be required.8,9

Although neuropathic pain may result from insults to both the central and peripheral nervous systems, most clinical studies have focused primarily on a small number of specific peripheral neuropathic pain syndromes. While pharmacological studies have been conducted in DPN, PHN and to some degree in trigeminal neuralgia (TN), spinal cord stimulation trials have been carried out in the neuropathic component of failed back surgery syndrome (FBSS) and in complex regional pain syndrome (CRPS). Thus, while evidence of efficacy of treatments in these indications clearly exists, the effectiveness of these treatments in other forms of neuropathic pain remains unclear.

Antidepressants
The tricyclic antidepressants (TCAs) are often regarded as first-line drugs for neuropathic pain. A recent systematic review of the literature, in which numbers needed to treat (NNTs) of treatments for different neuropathic pain syndromes were calculated, has found TCAs the most efficacious drugs for neuropathic pain (NNT 3.1; 95% confidence interval (CI) 2.7–3.7).5 This is based on results from no less than 15 placebo-controlled designed trials, which have uniformly demonstrated efficacy of amitriptyline, nortriptyline, desipramine, chlomipramine, imipramine and maprotiline, at a daily dose range of 30–200mg, for PHN and DPN. The main drawback of these trials is the small number of recruited patients in each of them. Yet, taken together, they provide strong level of evidence for efficacy. Notably, two small trials have found TCAs superior to placebo for central post-stroke pain and post-mastectomy neuropathic pain, whereas several others failed to demonstrate efficacy for spinal-cord injury pain, Human Immunodeficiency Virus (HIV) neuropathy and phantom limb pain. Unfortunately, TCAs are associated with numerous adverse events and are not tolerated by many patients. When used, slow titration is required, especially in the elderly.

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