The Diagnosis and Treatment of Neuropathic Pain

Abstract

Background: The reported prevalence of neuropathic pain in the general population in Germany is from 6.9% to 10%. There are both medical and surgical treatment options.

Methods: This review is based on pertinent publications retrieved by a selective search in PubMed, with consideration of clinical trials, meta-analyses, and guidelines.

Results: Neuropathic pain is diagnosed when pain of the appropriate character is accompanied by further features such as hypesthesia/anesthesia, allodynia, or hyperalgesia. It is generally treated initially with drugs (antidepressant drugs, anticonvulsant drugs, opioids, topical agents, and others); the number needed to treat (NNT) is between 7 and 8 for gabapentin and 3.6 for amitryptiline, as estimated in meta-analyses. For nerve compression and entrapment syndromes, surgical decompression is a treatment directed against the cause of the problem, which can therefore be curative. Microvascular decompression (MVD) is often used to treat supposed compression syndromes of cranial nerves, above all classic trigeminal neuralgia; according to a meta-analysis, MVD brings about a pain-free state in 92.9% [89.1; 96.8] of patients after 5 months to 5 years of follow-up. Ablative surgical procedures are used for symptom control in patients with refractory and/or cancer-related pain. Further symptomdirected treatment options for medically intractable neuropathic pain include neuromodulatory techniques, which involve minimally invasive electrical stimulation of neural structures, and the chronic intrathecal application of drugs such as opioids and ziconotide.

Conclusion: The treatment of neuropathic pain can be either cause-directed or symptom-directed, depending on its origin. Multidisciplinary collaboration can facilitate both the diagnostic evaluation and the selection of the optional modality and timing of treatment.

Figure 1

Flow chart to assess the diagnosis of neuropathic pain (modified from [12]). The graduation of the probability of neuropathic pain is based on the neurologic medical history and proved sensory deficits. In this setting, standardized questionnaires, electrophysiologic investigations, standardized neurologic investigative procedures such as quantitative sensory testing (QST) or the deduction of laser-evoked potentials (LEP), and, if needed, skin biopsies have important roles. QST allows testing the function of different sensory systems with standard stimuli and measuring thresholds of sensation semiquantitatively. A clinical validation of this classification regarding the treatments and their success rates is not available to date.

Figure 2

62-year-old (female) patient with stabbing pain in her right thumb and index finger. The Hoffman-Tinel sign on the inside of the elbow was positive. a) MR-neurography in the axial T2-weighted image shows a hyperintense inhomogeneous lesion over the course of the median nerve (white arrow), b) which, after contrast medium administration, shows in the T2-w image an intense inhomogeneous concentration (white arrow). c) The spatial allocation in the internal nerve structure is visible in the T2-w longitudinal section (white arrow: nerve lesion; yellow arrow: median nerve) d) and is especially visible on high-resolution neurosonography (white arrows: nerve lesion; yellow arrow: median nerve). The image prompted the suspicion of a schwannoma; this was histologically confirmed after resection. The patient was pain free after the operation and remained recurrence free.

Figure 3

56-year-old male patient with long-term type 2 diabetes and painful neuropathy. MR-neurography at the level of the distal sciatic nerve shows extensive fascicular signal increases in the peroneal (arrow) and tibial (dotted arrow) part of the sciatic nerve. Normally the nerve signal appears isointense to the surrounding thigh muscle.