Diagnosis and treatment of neuropathic pain

Update on pharmacotherapy guidelines for treatment of neuropathic pain

Neuropathic pain encompasses a myriad of painful disease states that are often hard to treat, especially with one single medication. In the comprehensive treatment of neuropathic pain, the concept of complex polypharmacy is a rational approach, accompanied by physical and mental health therapies. Medications primarily used for neuropathic pain generally fall into the categories of anticonvulsants, antidepressants, opioids, and topical agents. Generally, most first-line medications used today show a response rate of approximately 30% to 50% reduction in pain in up to 50% of patients treated. There is no "gold standard" in regard to one medication for neuropathic pain. Some new medications have emerged during the past few years that help to augment the armamentarium of medications used in neuropathic pain. This paper reviews the definition of neuropathic pain and introduces the reader to the evidence-based literature on these new medications available for the treatment of neuropathic pain.

Quantifying Allodynia in Patients Suffering From Unilateral Neuropathic Pain Using Von Frey Monofilaments

OBJECTIVES

The aim of this study is to investigate whether quantitative sensory testing with Von Frey monofilaments (VFMs) can be used for the quantification of allodynia in patients with chronic neuropathic pain, and how the pain threshold of affected skin differs from healthy skin.

METHODS

Using VFMs, we aimed to determine the pain threshold in 22 patients suffering from allodynia as a consequence of a chronic unilateral neuropathic pain syndrome. We performed quantitative sensory testing according to the Method of Limits protocol. We used the patient's own contralateral side and 5 healthy control participants to obtain reference values.

RESULTS

On the affected side, we found in 20 out of 22 patients that the pain threshold could be determined with the monofilaments. On average, these 20 patients indicated pain upon the application of monofilament with logarithmic nr. 4.56, whereas no pain threshold could be determined on the contralateral, unaffected side, and in the healthy control participants for any monofilament.

DISCUSSION

We showed that although etiology and pathophysiology of allodynia vary individually, with VFMs the clinical symptom allodynia can be quantified in a simple and practical fashion in almost all patients.

Use of gabapentine (neurantin) for relief of intractable pain developed after face-lift surgery

Complications of rhytidectomy, technically one of the most challenging operations of the aesthetic surgery, have been widely reported in the literature and nerve injuries are one of these possible complications during facial rejuvenation surgery. Beside the injuries of motor branches of the facial nerve, complaints of numbness and development of neuromas due to sensorial nerve injuries were reported in the literature. In this particular reported case, however, complaints of a 52-year-old woman, presented with diffuse intractable pain in her left cheek radiating to the neck and behind the ear after facial rejuvenation surgery, improved dramatically by use of gabapentine. Although there was no apparent neuroma formation on her neck, MRI findings are inconclusive and she had not responded to injection of local anesthetics at all.

Therapeutic Management of Chronic Neuropathic Pain: An Examination of Pharmacologic Treatment

Neuropathic pain is defined as pain caused by a lesion in the nervous system and is common in clinical practice. Diagnosis can be difficult. Recommendations for first-line pharmacologic treatments are based on positive results from multiple, randomized, controlled trials, and recommendations for second-line pharmacologic treatments are based on the positive result of a single, randomized, controlled trial or inconsistent results of multiple, randomized, controlled trials. The results of published trials and clinical experience provide the foundation for specific recommendations for first-line treatments, which include gabapentin, 5% lidocaine patch, opioid analgesics, tramadol hydrochloride, and tricyclic antidepressants (TCAs). Gabapentin (up to 3,600 mg/day) significantly reduced pain compared with placebo; improvements in sleep, mood, and quality of life were also demonstrated. Adverse effects of gabapentin include somnolence and dizziness, and, less commonly, gastrointestinal symptoms and mild peripheral edema. Thus, monitoring and dosage adjustment are required, without discontinuation of the drug. Gabapentin combined with morphine achieved better analgesia at lower doses of each drug than each drug alone, with only mild adverse effects. The first medication that proved effective for neuropathic pain in placebo-controlled trials was TCAs. Treatment decisions for patients with neuropathic pain can be difficult. Interest in the mechanisms and treatment of chronic neuropathic pain has increased during the past years, resulting in significant treatment advances in the future. In this article all recent knowledge on therapeutic management of chronic neuropathic pain is presented.

Antiallodynic effects of acupuncture in neuropathic rats

Peripheral nerve injury often results in abnormal neuropathic pain such as allodynia or hyperalgesia. Acupuncture, a traditional Oriental medicine, has been used to relieve pain and related symptoms. However, the efficiency of acupuncture in relieving neuropathic pain is not clear. The aim of this study was to investigate the anti-allodynic effects of acupuncture through behavioral and electrophysiological examinations. Male Sprague-Dawley rats were subjected to neuropathic surgery consisting of a tight ligation and transection of the left tibial and sural nerves, under pentobarbital anesthesia. The acupuncture experiment consisted of four different groups, one treated at each of three different acupoints (Zusanli (ST36), Yinlingquan (SP9), and a sham-acupoint) and a control group. Behavioral tests for mechanical allodynia and cold allodynia were performed for up to two weeks postoperatively. Extracellular electrophysiological recordings were made from the dorsal roots using platinum wire electrodes. Mechanical and cold allodynia were significantly reduced after acupuncture treatment at the Zusanli and Yinlingquan acupoints, respectively. Electrophysiological neural responses to von Frey and acetone tests were also reduced after acupuncture at the same two acupoints. These results suggest that acupuncture may be beneficial in relieving neuropathic pain.

Multimodality Treatment of Trigeminal Neuralgia

Most trigeminal neuralgia (TN) studies focus on a single strategy, microvascular decompression (MVD) or percutaneous rhizotomy (PR). We use a multimodality approach to TN. We perform MVD on patients younger than 70 years and PR on older patients or those where MVD has failed. We performed a chart review of the procedures for TN over the past 3 years and used a questionnaire for long-term follow-up. The questionnaire asked patients to rate their pre- and postoperative pain, outcome, and medication changes. Seventy-four procedures (40 MVDs and 34 PRs) were performed on 67 patients. Twenty patients had undergone previous procedures. 93% of the patients had significant initial pain relief. Over a 1.2-year mean follow-up, 51% of the patients had complete pain relief while 27% had a substantial improvement. There were no deaths and 5 complications. Our results suggest that a multimodality approach to TN yields excellent results with minimal complications.

Down-regulation of GFRalpha-1 expression by antisense oligodeoxynucleotide attenuates electroacupuncture analgesia on heat hyperalgesia in a rat model of neuropathic pain

Glial cell line-derived neurotrophic factor (GDNF) has been proved to play an important role in the modulation of nociceptive transmission especially during neuropathic pain. It was reported that electroacupuncture (EA) had potent analgesic effect on neuropathic pain and our previous studies indicated that EA could activate endogenous GDNF signaling system (GDNF and its receptor GFRalpha-1) in dorsal root ganglions (DRGs) of neuropathic pain rats. In order to investigate whether GDNF signaling system was involved in EA analgesia on neuropathic pain, which was induced by chronic constriction injury (CCI) of the sciatic nerve in rats, antisense oligodeoxynucleotide (ODN) specifically against GFRalpha-1 was used in the present study to result in down-regulation of GFRalpha-1 expression. The results showed that: (1) cumulative EA had potent analgesic effect on neuropathic pain in rats; (2) the expression of GFRalpha-1 in DRGs was down-regulated by intrathecal delivery of antisense ODN, but not by normal saline (NS) or mismatch ODN; (3) EA analgesia was significantly attenuated by antisense ODN treatment. The present study demonstrated that endogenous GDNF signaling system was involved in EA analgesia on neuropathic pain in rats, which would deepen our realization of the mechanism of EA analgesia.

Pain in primary care: an Italian survey

BACKGROUND

Pain is a universal symptom of various pathologies and largely affects human well-being. Pain is therefore commonly observed by general practitioners (GPs) and its management is a useful indicator of quality. In our study we investigated the epidemiology and management of pain in Italian general practice.

METHODS

Participating GPs were asked to record the first out of every two contacts with pain during two working weeks between November 2000 and February 2001. They entered information on type of pain, pain-related diagnosis, certainty of diagnosis and types of prescription.

RESULTS

89 GPs participated in the study. About one third of all reported contacts were with pain. The number of contacts analysed was 1432. Nearly half the cases were diagnosed as acute. The main complaints were of musculoskeletal and abdominal origin. Pain was 1.5 times more frequent in women than men and the female to male ratios for acute and chronic pain were 1.2:1 and 1.8:1 respectively. The most frequent site of pain was the limbs. 'Arthropathies and related disorders', 'dorsopathies' and 'rheumatism excluding the back' were the commonest groups of diagnoses. Approximately two thirds of contacts with pain led to a drug prescription.

CONCLUSIONS

The study identified a high proportion of contacts with pain in Italian general practice, with widespread use of drugs. The distribution of chronic and acute pain was rather similar and musculoskeletal pain was the most frequent form. Most types of prescriptions were closely related to certainty of diagnosis.

Design, Synthesis, and Preliminary Evaluation of Gabapentin-Pregabalin Mutual Prodrugs in Relieving Neuropathic Pain

As a part of a program for the development of specific analgesics in relieving neuropathic pain, the purpose of the present study was to investigate a new concept that involves the conjugation of two drugs, gabapentin and pregabalin, as mutual prodrugs using a chemical modification approach. A series of gabapentin-pregabalin diester compounds were synthesized using linear or branch bis-hydroxyl linkers. Their pharmacological properties for treating neuropathic pain were investigated in a rat model of chronic sciatic nerve constriction injury (CCI). In-vivo evaluation demonstrated that 1a and 1b composed of two gabapentin molecules as well as 3a composed of gabapentin and pregabalin with the short linear linker, were effective in reversing tactile allodynia in CCI rats. Compounds with longer or side-branched linkers showed lower efficiencies and severe adverse effects.

An 18-month follow-up study on vibrotactile sense, muscle strength and symptoms in computer users with and without symptoms

OBJECTIVES

The aim was to explore whether symptoms, sensory perception and muscle strength among computer users with and without symptoms in forearm or hand had changed after 18 months.

METHODS

Twenty-six out of 30 females, experienced computer users, from a baseline study participated in the follow-up. In addition, five control subjects participated. The subjects completed a questionnaire regarding exposure to computer work, prevalence and severity of symptoms, health status and physical activity. Perceived thresholds for vibration were measured twice with 3 h in between on the right hand on four different sites innervated by the radial, median or ulnar nerve. Furthermore, sensory perception was measured on the left hand on two sites innervated by the median and ulnar nerve, respectively. Skin temperature was measured at each site prior to sensory perception measurements. Maximal handgrip strength and maximal pinch-grip strength were measured for both hands.

RESULTS

Eighty-three percent of the subjects who had symptoms at baseline still had symptoms and 21% of the subjects who did not have symptoms at baseline experienced symptoms at follow-up. The first and the second sensory perception measurement were highly correlated. Vibrotactile sensory threshold representing the radial nerve was increased since baseline among the subjects who originally had symptoms. At follow-up, the vibrotactile sense for the computer users who reported symptoms in forearm or hand at baseline was deteriorated for the sites representing the median, ulnar and radial nerves compared to the control group. Among the original symptom free subjects with intensive computer work increases in vibrotactile perception thresholds were found for the sites representing the median and ulnar nerves. Handgrip muscle strength remained unchanged for all groups.

CONCLUSIONS

The study indicates that sensory dysfunctions as well as symptoms in forearm and hand among computer users to a high degree are persistent. Muscle strength seems to be well maintained.

Factors Associated with Self- and Caregiver Report of Pain among Community-Dwelling Persons with Dementia

BACKGROUND

Among cognitively intact patients, self- and caregiver report of patient pain has been associated with worse psychological health for both the patient and caregiver. Little existing research examines factors associated with patient self-report of pain and caregiver report of patient pain among community-dwelling persons with dementia.

OBJECTIVE

To identify patient and caregiver factors associated with self- and caregiver report of patient pain among community-dwelling persons with dementia.

DESIGN

Cross-sectional analysis of a longitudinal study using structured interviews with dementia patients and their family caregivers.

SETTING AND SUBJECTS

Urban outpatient geriatrics clinics affiliated with a university hospital. Dyads composed of dementia patients and their family caregivers were approached prior to routine clinic visits to participate in the study.

MEASUREMENTS

Relevant patient measurements included self-report of pain; cognitive, functional, and comorbidity assessments; a screen for depression; and demographic information. Relevant caregiver measurements included their report of patient pain and agitation, screens for depression and strain, and demographic information.

RESULTS

Of 115 dyads, 37 patients (32%) and 57 caregivers (53%) reported the patient to be in pain. No patient or caregiver factors were significantly associated with patient self-report of pain. In the univariate analysis, caregiver reports of patient pain were associated with the patient not being depressed (p = .036), caregiver reports of patient agitation (p = .038), higher level of education in the caregiver (p = .029), and caregiver depression (p = .019). In multivariate logistic regression analyses, caregiver depression and patient agitation remained significantly associated with caregiver report of patient pain.

CONCLUSIONS

In community-dwelling persons with dementia, self-report of pain was not associated with any other variables measured, suggesting that pain should be assessed through direct self-report and treated accordingly. Caregiver report of patient pain was associated with both caregiver report of patient agitation and caregiver depression. These findings suggest that clinicians may need to routinely assess patient pain, patient agitation, and caregiver depression. More research is needed to understand the relationship between these conditions.

Current trends in neuropathic pain treatments with special reference to fibromyalgia

Neuropathic pain and fibromyalgia are prevalent diseases which have major consequences on healthcare resources and the individual. From the clinical point of view neuropathic pains represent a heterogeneous group of aetiologically different diseases ranging from cancer to diabetes. Patients with fibromyalgia also display clinical features common in neuropathic pain suggesting that there might be some overlap. The mechanisms responsible for symptoms and signs in both diseases are still unknown. Recently, there have been numerous reports of various pharmacological treatments of neuropathic pain and fibromyalgia with often disappointing results. Most of the studies were of short duration, had high attrition rates, and displayed other methodological problems. Some compounds had high rates of adverse effects which makes it often difficult for the patients to tolerate the treatment, especially in the long-term. At present, the best options for medication treatment are tricyclic antidepressants in lower dosage than usual in psychiatric disorders and a wide range of anticonvulsants. Opioids are sometimes recommended but have been found to have minor efficacy. Recently, there have been more controlled trials, which are reported here if they had been published between 2002 and 2004. Various compounds have been tested in different studies. Treatment of fibromyalgia, which has many features in common with depressive symptoms, became the focus of interest. New promising studies with dual serotonin-norepinephrine reuptake inhibitors (duloxetine and milnacipram) and a newer antiepileptic drug (pregabalin) are in progress. Future research will have to apply new approaches (e.g., using a mechanism-based classification of neuropathic pain and carrying out studies in populations with the same symptom but not necessarily the same disease) in order to find effective treatments for these common and often debilitating diseases.

Management of cancer pain

There are four basic approaches to cancer pain control: modify the source of pain, alter central perception of pain, modulate transmission of pain to the central nervous system, and block transmission of pain to the central nervous system. Systemic pharmacologic management aimed at the first three of these approaches is the cornerstone of the treatment of most cancer patients with moderate to severe pain. Optimal pharmacologic management of cancer pain requires selection of the appropriate analgesic drug; prescription of the appropriate dose; administration of the analgesic by the appropriate route; scheduling of the appropriate dosing interval; prevention of persistent pain and relief of breakthrough pain; aggressive titration of the dose of the analgesic; prevention, anticipation, and management of analgesic side effects; consideration of sequential trials of opioid analgesics; and use of appropriate co-analgesic drugs for specific pain syndromes. Most clinicians should be able to control most of the pain in most of their cancer patients. Collaboration with pain and hospice/palliative care experts should help the rest. No cancer patient should live or die with unrelieved pain.

Pathophysiology of neuropathic pain

Neuropathic pain is caused by damage to the nervous system. Unlike physiologic pain (also known as nociceptive pain), neuropathic pain is not self-limited and is not as easily treated. The etiologic causes of neuropathic pain are many and varied in their scope. These include infectious agents, metabolic disease, neurodegenerative disease, and physical trauma, among others. Clinically, a high degree of variability exists between patients in their response to treatment. The pathophysiology of neuropathic pain syndromes is complex. However, current research is rapidly expanding our understanding of these syndromes. Numerous cellular mechanisms of pain transmission have been elucidated, and the clinical correlates of these mechanisms are beginning to be recognized. As our knowledge base continues to grow, we anticipate the development of improved treatments for the benefit of our patients with pain.

Oxcarbazepine in painful diabetic neuropathy: a randomized, placebo-controlled study

In this multicentre, placebo-controlled, 16-week trial, the efficacy and safety of oxcarbazepine monotherapy in patients with neuropathic pain of diabetic origin was evaluated. Eligible patients had a 6-month to 5-year history of neuropathic pain symptoms of diabetic origin and a pain rating of > or =50 units on the visual analogue scale (VAS). Oxcarbazepine was initiated at a dose of 300 mg/day and titrated to a maximum dose of 1800 mg/day. In total, 146 patients (oxcarbazepine, n=69; placebo, n=77) were randomized. After 16 weeks, oxcarbazepine-treated patients experienced a significantly larger decrease in the average change in VAS score from baseline compared with placebo (-24.3 vs. -14.7 units, respectively; p=0.01). The reduction from baseline in mean VAS score for oxcarbazepine-treated patients was of a greater magnitude than placebo as early as week 2 (-8.0 vs. -4.7; p<0.05). A significantly greater proportion of oxcarbazepine-treated patients experienced a >50% reduction from baseline in VAS score at the end of treatment compared with placebo (35.2% vs. 18.4%, respectively; p=0.0156; number needed to treat=6.0). Global assessment of therapeutic effect rating was improved in more oxcarbazepine patients than placebo patients (48% vs. 22%, respectively; p=0.0025). Patients on oxcarbazepine were awakened less frequently due to pain than patients on placebo. Most adverse events were mild to moderate in severity, transient, and in line with the known tolerability profile of oxcarbazepine. These observations suggest that oxcarbazepine monotherapy, pending additional trials, may be efficacious and may provide clinically meaningful pain relief in patients with neuropathic pain of diabetic origin.

Neuropathic pain: A guide to comprehensive assessment

Patients with neuropathic pain present a clinical challenge. Neuropathic pain, when chronic, often leads to disability. Diagnosis can be difficult because both positive and negative sensory and motor signs and symptoms may be present, as well as a variety of comorbid conditions. In addition, there may be a high degree of interpatient variability. Currently, clinical evaluation, rather than diagnostic tests, is one of the best available tools for assessment and diagnosis. As with all chronic pain conditions, the key to a thorough assessment is a thorough history that includes medical, functional, and psychosocial evaluations. Currently available pain assessment tools, which are widely used in nursing practice, are still inadequate for use in patients with neuropathic pain. The physical and neurologic examination remains a critical element for patient evaluation. This includes an assessment of spontaneous pain (continuous or intermittent), pain evoked by daily activities (allodynia), and other abnormal sensations that are not necessarily painful (paresthesias, dysesthesias). Sensitivity to pinprick, touch, pressure, cold, heat, and vibration are measured, often confirming the suspected diagnosis. Patients may be confused by the unusual sensations they are experiencing and unable to effectively describe or communicate their symptoms. This communication barrier may contribute to an inadequate physical examination. With improved skills in patient assessment and through enhanced communication with patients, nurses can make an important contribution to treatment outcomes in patients with neuropathic pain.

A treatment algorithm for neuropathic pain

BACKGROUND

Neuropathic pain is a chronic pain syndrome caused by drug-, disease-, or injury-induced damage or destruction of sensory neurons within the dorsal root ganglia of the peripheral nervous system. Characteristic clinical symptoms include the feeling of pins and needles; burning, shooting, and/or stabbing pain with or without throbbing; and numbness. Neuronal hyperexcitability represents the hallmark cellular mechanism involved in the underlying pathophysiology of neuropathic pain. Although the primary goal is to alleviate pain, clinicians recognize that even the most appropriate treatment strategy may be, at best, only able to reduce pain to a more tolerable level.

OBJECTIVE

The purpose of this review is to propose a treatment algorithm for neuropathic pain that health care professionals can logically follow and adapt to the specific needs of each patient. The algorithm is intended to serve as a general guide to assist clinicians in optimizing available therapeutic options.

METHODS

A comprehensive review of the literature using the PubMed, MEDLINE, Cochrane, and Toxnet databases was conducted to design and develop a novel treatment algorithm for neuropathic pain that encompasses agents from several drug classes, including antidepressants, antiepileptic drugs, topical antineuralgic agents, narcotics, and analgesics, as well as various treatment options for refractory cases.

RESULTS

Any of the agents in the first-line drug classes (tricyclic antidepressants, antiepileptic drugs, topical antineuralgics, analgesics) may be used as a starting point in the treatment of neuropathic pain. If a patient does not respond to treatment with at least 3 different agents within a drug class, agents from a second drug class may be tried. When all first-line options have been exhausted, narcotic analgesics or refractory treatment options may provide some benefit. Patients who do not respond to monotherapy with any of the first- or second-line agents may respond to combination therapy or may be candidates for referral to a pain clinic. Because the techniques used at pain clinics tend to be invasive, referrals to these clinics should be reserved for patients who are truly refractory to all forms of pharmacotherapy.

CONCLUSIONS

Neuropathic pain continues to be one of the most difficult pain conditions to treat. With the proposed algorithm, clinicians will have a framework from which to design a pain treatment protocol appropriate for each patient. The algorithm will also help streamline referrals to specialized pain clinics, thereby reducing waiting list times for patients who are truly refractory to traditional pharmacotherapy.

The management of malignant psoas syndrome: case reports and literature review

Malignant psoas syndrome (MPS) was first described in 1990, and is characterized by proximal lumbosacral plexopathy, painful fixed flexion of the ipsilateral hip, and radiological or pathological evidence of ipsilateral psoas major muscle malignant involvement. There have been 23 case reports of MPS in medical journals. Despite being associated with a severe and difficult pain, there is no definitive approach to management presented in the palliative care literature. We review the relevant clinical features and the subsequent multidisciplinary pain management in relation to four new cases of malignant involvement of the psoas muscle, and the 23 case reports in the literature. We propose that MPS comprises a continuum of symptoms and signs related to the degree of anatomical destruction with associated inflammatory reaction and muscle spasm, and also the degree of lumbosacral plexopathy causing neuropathic pain. A protocol is presented for the management of the complex pain issues of MPS directed at likely mechanisms. The treatment options include opioids, agents for neuropathic pain, muscle relaxants to manage psoas muscle spasm, and anti-inflammatory agents to reduce peritumoral edema. Direct anti-tumor measures also need to be considered. Further prospective study is needed to validate the proposed methods of assessment and treatment.

Painful peripheral neuropathy and its nonsurgical treatment

Treatment of neuropathic pain is the primary focus of management for many patients with painful peripheral neuropathy. Antidepressants and anticonvulsants are the two pharmacological classes most widely studied and represent first-line agents in the management of neuropathic pain. The number of pharmacological agents that have demonstrated effectiveness for neuropathic pain continues to expand. In the current review, we summarize data from randomized, controlled pharmacological trials in painful peripheral neuropathies. Although neuropathic pain management remains challenging because the response to therapy varies considerably between patients, and pain relief is rarely complete, a majority of patients can benefit from monotherapy using a well-chosen agent or polypharmacy that combines medications with different mechanisms of action.