EFNS guidelines on neuropathic pain assessment

An investigation of somatosensory profiles in work related upper limb disorders: a case-control observational study protocol

Background

Work related upper limb disorders constitute 45% of all occupational diseases and are a significant public health problem. A subgroup, non specific arm pain (NSAP), remains elusive in terms of understanding its pathophysiological mechanisms with its diagnosis based on the absence of specific clinical findings. One commonly proposed theory is that a neural tissue disorder is the primary dysfunction in NSAP and findings from previous studies lend some support to this theory. However, it is not clear if changes identified are simply a consequence of ongoing pain rather than due to specific neural changes. The presence of neuropathic pain has been investigated in several other musculoskeletal conditions but currently, there is no specific diagnostic tool or gold standard which permits an unequivocal diagnosis of neuropathic pain. The purpose of this study is to further describe the somatosensory profiles in patients with NSAP and to compare these profiles to a group of patients with MRI confirmed cervical radiculopathy who have been previously classified as having neuropathic pain.

Methods/Design

Three groups of participants will be investigated: Groups 1 and 2 will be office workers with either NSAP or cervical radiculopathy and Group 3 will be a control group of non office workers without upper limb pain. Participants will undergo a clinical assessment, pain questionnaires (LANSS, Short Form McGill, DASH and TSK) and quantitative sensory testing comprising thermal detection and pain thresholds, vibration thresholds and pressure pain thresholds.

Discussion

The spectrum of clinically suspected neuropathic pain ranges from more obvious conditions such as trigeminal neuralgia to those with vague signs of nerve disorder such as NSAP. A thorough description of the somatosensory profiles of NSAP patients and a comparison with a more defined group of patients with evidence of neuropathic pain will help in the understanding of underlying neurophysiology in NSAP and may influence future classification and intervention studies relating to this condition.

Sensory changes and loss of intraepidermal nerve fibers in painful unilateral nerve injury

OBJECTIVES

Dysaesthesias is a common symptom in patients with neuropathic pain after peripheral nerve injury (PNI). In contrast to neuropathies with comparable symptoms there is little knowledge of the underlying mechanisms in PNI patients.

METHODS

Quantitative sensory testing according to the German Research Network on Neuropathic Pain protocol, and changes in intraepidermal nerve fiber density were assessed in 15 patients with dysaesthesias after PNI of the lower limb. According to their small-fiber function patients were assigned into 2 subgroups.

RESULTS

The sensory profiles of PNI patients were characterized predominantly by minus symptoms (significantly increased thresholds for perception of cold, warm, touch and vibration, and significantly increased thresholds for heat and mechanical pain) on the affected compared with the unaffected side. The only plus symptom reported was a significantly reduced pressure pain threshold. The sensory profile of patients with a severe loss of small-fiber function (n=7) showed a thermal and tactile hypoaesthesia and hypoalgesia; this was in contrast to patients with a moderate loss of small-fiber function, who showed a mild thermal and tactile hypoaesthesia associated with an increased mechanical pain sensitivity. Mean intraepidermal nerve fiber density was significantly decreased in the affected compared with unaffected skin [3.50 (4.00) vs. 11.10 (7.60) fibers/mm] and correlated with warm and mechanical detection thresholds (both r=-0.60).

DISCUSSION

In conclusion, even though patients presented with comparable clinical symptoms, their sensory profiles differed, supporting the concept of different underlying mechanisms leading to chronic pain in PNI patients. Skin biopsies support the validity of quantitative sensory testing.

Cranial neuralgias

After a description of the anatomical-functional organization of the human trigeminal system, this chapter discusses the diagnostic and therapeutic options for trigeminal neuralgia (TN). In about 15% of patients who present with the clinical picture of typical TN, this is secondary to a major neurological disease, i.e., benign tumors of the cerebellopontine angle or multiple sclerosis. Some clinical criteria that were used to distinguish between classic and symptomatic TN, such as age at onset, involvement of the ophthalmic division, and responsiveness to medical treatment, are no longer considered reliable. It is recommended that all patients undergo magnetic resonance imaging (MRI) or trigeminal reflex recording. Carbamazepine (CBZ) and oxcarbazepine (OXC) are the first-choice medical treatments. Although other drugs may be effective, these are indicated when the patient cannot reach the therapeutic dosage of CBZ/OXC because of adverse events. Patients unresponsive to CBZ/OXC should be made aware of the available surgical interventions. Surgical procedures (including percutaneous lesions to the ganglion/root, microvascular decompression (MVD) in the posterior fossa, and gamma knife radiosurgery) are extremely efficacious with relatively few complications: each procedure has some advantage and disadvantage with respect to the other. Only MVD is a non-destructive procedure. This chapter also describes management of glossopharyngeal neuralgia, which is often misdiagnosed, and some other chronic pain conditions mediated by the trigeminal system, such as ophthalmic postherpetic neuralgia (PHN).

Evaluation of pain measurement practices and opinions of peripheral nerve surgeons

The purpose of this study was to evaluate the opinions and practices of peripheral nerve surgeons regarding assessment and treatment of pain in patients following nerve injury. Surgeons with expertise in upper extremity peripheral nerve injuries and members of an international peripheral nerve society were sent an introductory letter and electronic survey by email (n = 133). Seventy members responded to the survey (49%) and 59 surgeons completed the survey (44%). For patients referred for motor or sensory dysfunction, 31 surgeons (52%) indicated that they always formally assess pain. In patients referred for pain, 44 surgeons (75%) quantitatively assess pain using a verbal scale (n = 24) or verbal numeric scale (n = 36). The most frequent factors considered very important in the development of chronic neuropathic pain were psychosocial factors (64%), mechanism of injury (59%), workers' compensation or litigation (54%), and iatrogenic injury (48%). In patients more than 6 months following injury, surgeons frequently see: cold sensitivity (54%), decreased motor function (42%), paraesthesia or numbness (41%), fear of returning to work (22%), neuropathic pain (20%), and emotional or psychological distress (17%). Only 52% of surgeons who responded to the survey always evaluate pain in patients referred for motor or sensory dysfunction. Pain assessment most frequently includes verbal patient response, and assessment of psychosocial factors is rarely included. Predominately, patient-related factors were considered important in the development of chronic neuropathic pain.

Guidelines for the diagnosis and management of neuropathic pain: consensus of a group of Latin American experts

These consensus guidelines have been developed by a group of Latin American experts in pain management, to point out patterns and make practical recommendations to guide the diagnosis, identify warning signs (yellow and red flags), and establish comprehensive medical management (pharmacologic and nonpharmacologic treatment) and monitoring plans for patients enduring neuropathic pain. From the viewpoint of pharmacologic management, drugs are classified into groups according to efficacy, availability/accessibility, and safety criteria. Drugs are recommended for use depending on the disease and particular circumstances of each patient, with an approach that favors multimodal treatment while taking into consideration the idiosyncrasies of medical practice in Latin America.

Quantitative sensory testing and mapping: a review of nonautomated quantitative methods for examination of the patient with neuropathic pain

OBJECTIVES

Despite a growing interest in neuropathic pain, neurologists and pain specialists do not have a standard, validated, office examination for the evaluation of neuropathic pain signs to complement the neurologic, musculoskeletal, and general physical examinations. An office neuropathic pain examination focused on quantifying sensory features of neuropathic pain, ranging from deficits to allodynia and hyperalgesia, and evoked by a physiologically representative array of stimuli, will be an essential tool to monitor treatment effectiveness and for clinical investigation into the mechanisms and management of neuropathic pain. Such an examination should include mapping of areas of stimulus-evoked neuropathic pain and standardized, reproducible quantitative sensory testing (QST) of tactile, punctuate, pressure, and thermal modalities.

METHODS

We review quantitative sensory testing methodology in general and specific tests for the evaluation of neuropathic pain phenomena.

RESULTS

Numerous quantitative sensory testing techniques for dynamic mechanical, pressure, vibration, and thermal sensory testing and mapping have been described. We propose a comprehensive neuropathic pain evaluation protocol that is based upon these available techniques.

CONCLUSIONS

A comprehensive neuropathic pain evaluation protocol is essential for further advancement of clinical research in neuropathic pain. A protocol that uses tools readily available in clinical practice, when established and validated, can be used widely and thus accelerate data collection for clinical research and increase clinical awareness of the features of neuropathic pain.

An MR-compatible device for automated and safe application of laser stimuli in experiments employing nociceptive stimulation

In this paper the establishment of an automatic laser application device that reproducibly delivers laser stimuli in a safe, controlled, and reliable manner is presented. Nociceptive stimulation is widely used in functional magnetic resonance imaging (fMRI) experiments and a number of different methods are employed. One major advantage of laser stimulation as a method to administer painful stimuli is that it selectively activates nociceptors. To avoid damage to the subject's skin, which might occur if the same skin area were stimulated too often, the laser focal spot needs to be repositioned after each stimulus. Here, we describe the design of the mechanical set-up, the functionality, the computation of laser stimulus intensity, the materials used, the monitoring system, and the interface to the control software. Additionally, MR-compatibility and functionality of the device were evaluated and assessed in a 3T MR scanner. Finally, the reliability and validity of the device were tested and demonstrated. It permits easy and investigator-independent use of laser stimulation in the MR scanner.

Postherpetic neuralgia: from preclinical models to the clinic

Postherpetic neuralgia (PHN), a common complication of herpes zoster, which results from reactivation of varicella zoster virus, is a challenging neuropathic pain syndrome. The incidence and severity of herpes zoster and PHN increases with immune impairment or age and may become a greater burden both in terms of health economics and individual suffering. A clearer understanding of the underlying mechanisms of this disease and translation of preclinical outcomes to the clinic may lead to more efficacious treatment options. Here we give an overview of recent findings from preclinical models and clinical research on PHN.

Assessment of neuropathic pain in primary care

Management of patients presenting with chronic pain is a common problem in primary care. Essentially, the classification of chronic pain falls into 3 broad categories: (1) pain owing to tissue disease or damage (nociceptive pain), (2) pain caused by somatosensory system disease or damage (neuropathic pain), and (3) pain without a known somatic background. Key challenges in developing a targeted holistic approach to treatment include appropriate diagnosis of the cause or causes of pain; identifying the type of pain and assessing the relative importance of its various components; and determining appropriate treatment. In clinical examination, sensory abnormalities are the crucial findings leading to a diagnosis of neuropathic pain, for which pharmacotherapy with antidepressants and anticonvulsants represents the cornerstone of medical treatment. Chronic neuropathic pain is underrecognized and undertreated, yet primary care physicians are uniquely placed on the frontlines of patient management, where they can play a pivotal role in treatment and prevention through diagnosis, therapy, follow-up, and referral. This review provides guidance in understanding and identifying the neuropathic contribution to pain presenting in primary care; assessing its severity through patient history, physical examination, and appropriate diagnostic tests; and establishing a rational treatment plan.

Neuroimaging as a tool for pain diagnosis and analgesic development

Neuroimaging makes it possible to study pain processing beyond the peripheral nervous system, at the supraspinal level, in a safe, noninvasive way, without interfering with neurophysiological processes. In recent years, studies using brain imaging methods have contributed to our understanding of the mechanisms responsible for the development and maintenance of chronic pain. Moreover, neuroimaging shows promising results for analgesic drug development and in characterizing different types of pain, bringing us closer to development of mechanism-based diagnoses and treatments for the chronic pain patient.

Revised definition of neuropathic pain and its grading system: an open case series illustrating its use in clinical practice

The definition of neuropathic pain has recently been revised by an expert committee of the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain (NeuPSIG) as "pain arising as direct consequence of a lesion or disease affecting the somatosensory system," and a grading system of "definite," "probable," and "possible" neuropathic pain has been introduced. This open case series of 5 outpatients (3 men, 2 women; mean age 48 +/- 12 years) demonstrates how the grading system can be applied, in combination with appropriate confirmatory testing, to diagnosis neuropathic conditions in clinical practice. The proposed grading system includes a dynamic algorithm that enhances the physician's ability to determine with a greater level of certainty whether a pain condition is neuropathic. Its clinical use should be further validated in prospective studies.

Evaluation of symptom heterogeneity in neuropathic pain using assessments of sensory functions

Classification of neuropathic pain has been based on disease entities, anatomical localization, or histological observations. Over the past decade, there has been an explosion in our understanding of the basic mechanisms of neuropathic pain. The exciting advances in basic science are paralleled by the recognition from clinical investigations that neuropathic pain is not a monolithic entity, but instead presents as a composite of pain and other sensory symptoms. Attempts are under way to supplement the traditional classification with a classification that links pain and sensory symptoms with neurobiological mechanisms. This mechanism- or symptom-based classification takes both negative and positive sensory symptoms into account. By using a battery of several standardized quantitative sensory tests, the characteristic profile of sensory symptoms can be elucidated in each patient. Moreover, in questionnaires the verbal descriptors can depict the quality and intensity of the individual pain. The approach of classifying and subgrouping patients with neuropathic pain on the basis of symptoms or signs opens up new possibilities for stratifying patients in clinical trials. First, in clinical proof-of-concept trials the study population can be enriched prospectively on the basis of entry criteria defined a priori. This enrichment with patients who potentially require a specific treatment should increase the likelihood for positive trial outcomes. Second, in clinical practice it becomes possible to establish an individualized therapy--that is, to identify the particular patients who require a specific treatment option.

What do general neurologists need to know about neuropathic pain?

Neuropathic pain (NP) is defined as pain caused by lesion or dysfunction of the somatosensory system, as a result of abnormal activation of the nociceptive pathway (small fibers and spinothalamic tracts). The most common causes of this syndrome are the following: diabetes, post-herpetic neuralgia, trigeminal neuralgia, stroke, multiple sclerosis, spinal cord injury, HIV infection, cancer. In the last few years, the NP has been receiving special attention for two main reasons: (1) therapeutical refractoriness of a variety of pain syndromes with predominant neuropathic characteristics and (2) the development of diagnostic tools for neuropathic pain complaints. The present review article provides relevant information on the understanding and recognition of NP, as well as evidence-based therapeutic approaches.

Sensitisation of spinal cord pain processing in medication overuse headache involves supraspinal pain control

Medication overuse could interfere with the activity of critical brain regions involved in the supraspinal control of pain signals at the trigeminal and spinal level, leading to a sensitisation phenomenon responsible for chronic pain. We hypothesised that medication-overuse headache (MOH) patients might display abnormal processing of pain stimuli at the spinal level and defective functioning of the diffuse noxious inhibitory controls. We tested 31 MOH patients before (bWT) and after (aWT) standard inpatient withdrawal treatment, 28 episodic migraine (EM) patients and 23 healthy control subjects. We measured the threshold, the area and the temporal summation threshold (TST) of the nociceptive withdrawal reflex before, during and after activation of the diffuse noxious inhibitory controls by means of the cold pressor test. A significantly lower TST was found in both the MOH (bWT and aWT) and the EM patients compared with the controls, and in the MOH patients bWT compared with both the MOH patients aWT and the EM patients. In the MOH bWT patients the cold pressor test induced a TST increase significantly lower than that found in the MOH aWT, EM and control groups. Abnormal spinal cord pain processing and a decrease of the antinociceptive activity of the supraspinal structures in MOH patients can be hypothesised. These abnormalities could, in part, be related to the medication overuse, given that the withdrawal treatment was related to an improvement in the neurophysiological findings.

Electric toothbrush application is a reliable and valid test for differentiating temporomandibular disorders pain patients from controls

BACKGROUND

Current methods for identifying patients with pain hypersensitivity are sufficiently complex to limit their widespread application in clinical settings. We assessed the reliability and validity of a simple multi-modal vibrotactile stimulus, applied using an electric toothbrush, to evaluate its potential as a screening tool for central sensitization.

METHODS

Fourteen female temporomandibular disorders (TMD) subjects with myofascial pain (RDC/TMD Ia or Ib) and arthralgia (RDC/TMD IIIa) were compared to 13 pain-free controls of matched age and gender. Vibrotactile stimulus was performed with an electric toothbrush, applied with 1 pound pressure for 30 seconds in four locations: over the lateral pole of the temporomandibular joint, masseter, temporalis, and mid-ventral surface of forearm. Pain intensity (0-10) was recorded following the stimulus at 0, 15, 30, and 60 seconds. Test-retest reliability was assessed with measurements from 8 participants, taken 2-12 hours apart. Case versus control differentiation involved comparison of area under the curve (AUC). A receiver operating characteristic (ROC) curve was used to determine cutoff AUC scores for maximum sensitivity and specificity for this multi-modal vibrotactile stimulus.

RESULTS

Test-retest reliability resulted in an ICC of 0.87 for all 4 pooled sites. ROC-determined AUC cutoff scores resulted in a sensitivity of 57% and specificity of 92% for all 4 pooled sites.

CONCLUSION

The electric toothbrush stimulus had excellent test-retest reliability. Validity of the scores was demonstrated with modest sensitivity and good specificity for differentiating TMD pain patients from controls, which are acceptable properties for a screening test.

Topical 5% lidocaine (lignocaine) medicated plaster treatment for post-herpetic neuralgia: results of a double-blind, placebo-controlled, multinational efficacy and safety trial

BACKGROUND AND OBJECTIVE

Post-herpetic neuralgia (PHN) is a distressing neuropathic pain condition mainly affecting elderly patients. Neuropathic pain symptoms can be of a burning, shooting and stabbing nature, and may continue for prolonged periods and are often poorly controlled by polymedication. The aim of this study was to evaluate the analgesic efficacy and safety of topical analgesic treatment (5% lidocaine [lignocaine] medicated plaster) compared with placebo plaster in patients with PHN.

METHODS

This was a double-blind, placebo plaster-controlled, parallel-group, multicentre study employing enriched enrolment with randomized withdrawal methodology. After an initial 8-week open-label, active run-in phase, responders entered a 2-week randomized, double-blind, placebo-controlled phase. The study was conducted at 33 outpatient investigational centres in 12 European countries. Patients with PHN were selected who were aged >/=50 years, had experienced neuropathic pain persisting for >/=3 months after rash healing, and had a mean pain intensity of >/=4 on an 11-point numerical rating scale. A total of 265 patients entered the open-label phase and subsequently a pre-defined number of 71 patients entered the randomized phase. Patients applied up to three 5% lidocaine medicated plasters for up to 12 hours per day. The primary endpoint of the study was time-to-exit due to a >/=2-point reduction in pain relief on two consecutive days of plaster application using a 6-point verbal rating scale.

RESULTS

Of the 265 patients entering the run-in phase, 51.7% achieved at least moderate pain relief. In the double-blind phase (full analysis set, n = 71), median times-to-exit were 13.5 (range 2-14) and 9.0 (range 1-14) days for lidocaine and placebo plaster groups, respectively (p = 0.151). For per-protocol patients (n = 34), median time-to-exit was 14.0 (range 3-14) and 6.0 (range 1-14) days for lidocaine and placebo plaster groups, respectively (p = 0.0398). Drug-related adverse events occurred in 13.6% of patients. Treatment with 5% lidocaine medicated plaster was associated with improvements in pain, allodynia, quality of life and sleep measures.

CONCLUSIONS

This study adds to a growing body of evidence that the 5% lidocaine medicated plaster can be considered a valuable treatment option for patients with PHN, providing beneficial effects on pain, allodynia, quality of life and sleep, with minimal adverse effects.

Pain measurements and side effect profile of the novel cannabinoid ajulemic acid

Preclinical findings on ajulemic acid (AJA) showed analgesic and anti-allodynic effects without psychoactive properties making it an appealing substance for the treatment of pain. A recently published randomized double-blind crossover clinical trial described the pain-reducing effects and side effect profile of AJA on 21 patients with chronic neuropathic pain. In this report from this same sample the effects of AJA on the mechanical hypersensitivity, on pain, and on psychological and physical performance were further characterized. During a 5-week study period, patients were divided into two 7-day treatment groups receiving either AJA or placebo capsules first, respectively. All patients received 40 and 80 mg of AJA or placebo daily in each treatment period. Pain measurements included the determination of mechanical hypersensitivity using the von Frey hair method as well as the visual analog scale (VAS), for which the number needed to treat (NNT) was calculated. The side effect profile of the compound was evaluated using psychotropic and physical measurements as well as obtaining reports on possible subjective side effects. The results showed no significant reduction in mechanical hypersensitivity (p=0.052), although a tendency towards pain reduction could be seen. The VAS score showed significant pain reduction (p=0.021) and NNT values for 30% pain relief were 2.14 for the first treatment group and 5.29 for the second treatment group. No significant findings were observed regarding psychotropic or physical measurements. Reported subjective side effects were mainly dry mouth, tiredness and dizziness and did not increase with dose elevation. Overall, these study findings indicate that AJA shows pain-reducing effects on patients with chronic neuropathic pain without clinically relevant psychotropic or physical side effects.

A cross-sectional cohort survey in 2100 patients with painful diabetic neuropathy and postherpetic neuralgia: Differences in demographic data and sensory symptoms

Patients with neuropathic pain syndromes are heterogeneous. They present with a variety of sensory symptoms and pain qualities. The knowledge of these data and etiology-specific differences is important to optimize clinical trial design and to develop more effective drugs. This investigation uses epidemiological and clinical data on the symptomatology of 2100 patients with painful diabetic neuropathy (DPN) and postherpetic neuralgia (PHN) from a cross-sectional survey (painDETECT) to (1) describe characteristic epidemiological differences, (2) analyse typical patterns of sensory symptoms in both cohorts and (3) determine whether questionnaires can capture these characteristics. PHN patients suffer more often from clinically relevant sensory disturbances although the average pain intensity is only marginally higher. This difference is particularly obvious with dynamic mechanical allodynia which is present in half of the PHN patients and in 18% of the DPN patients. Thermal hyperalgesia occurs twice as often in PHN. Numbness is described more often in DPN. Age has no influence on sensory symptoms in both entities. A hierarchical cluster analysis revealed five distinct subgroups of patients showing a characteristic sensory profile, a typical constellation and combination of neuropathic symptoms. All subgroups occur in relevant numbers in both entities but the frequencies differ between PHN and DPN. Since sensory symptoms likely translate into pain-generating mechanisms enrichment for potential treatment responders might be possible in clinical trials by assessing the sensory profiles. Patient-Reported Outcomes can be used to obtain a precise sensory characterization of each patient.

5% lidocaine medicated plaster versus pregabalin in post-herpetic neuralgia and diabetic polyneuropathy: an open-label, non-inferiority two-stage RCT study

OBJECTIVE

To compare efficacy and safety of 5% lidocaine medicated plaster with pregabalin in patients with post-herpetic neuralgia (PHN) or painful diabetic polyneuropathy (DPN).

STUDY DESIGN AND METHODS

This was a two-stage adaptive, randomized, open-label, multicentre, non-inferiority study. Data are reported from the initial 4-week comparative phase, in which adults with PHN or painful DPN received either topical 5% lidocaine medicated plaster applied to the most painful skin area or twice-daily pregabalin capsules titrated to effect according to the Summary of Product Characteristics. The primary endpoint was response rate at 4 weeks, defined as reduction averaged over the last three days from baseline of > or = 2 points or an absolute value of < or = 4 points on the 11-point Numerical Rating Scale (NRS-3). Secondary endpoints included 30% and 50% reductions in NRS-3 scores; change in allodynia severity rating; quality of life (QoL) parameters EQ-5D, CGIC, and PGIC; patient satisfaction with treatment; and evaluation of safety (laboratory parameters, vital signs, physical examinations, adverse events [AEs], drug-related AEs [DRAEs], and withdrawal due to AEs).

RESULTS

Ninety-six patients with PHN and 204 with painful DPN were analysed (full analysis set, FAS). Overall, 66.4% of patients treated with the 5% lidocaine medicated plaster and 61.5% receiving pregabalin were considered responders (corresponding numbers for the per protocol set, PPS: 65.3% vs. 62.0%). In PHN more patients responded to 5% lidocaine medicated plaster treatment than to pregabalin (PPS: 62.2% vs. 46.5%), while response was comparable for patients with painful DPN (PPS: 66.7% vs 69.1%). 30% and 50% reductions in NRS-3 scores were greater with 5% lidocaine medicated plaster than with pregabalin. Both treatments reduced allodynia severity. 5% lidocaine medicated plaster showed greater improvements in QoL based on EQ-5D in both PHN and DPN. PGIC and CGIC scores indicated greater improvement for 5% lidocaine medicated plaster treated patients with PHN. Improvements were comparable between treatments in painful DPN. Fewer patients administering 5% lidocaine medicated plaster experienced AEs (safety set, SAF: 18.7% vs. 46.4%), DRAEs (5.8% vs. 41.2%) and related discontinuations compared to patients taking pregabalin.

CONCLUSION

5% lidocaine medicated plaster showed better efficacy compared with pregabalin in patients with PHN. Within DPN, efficacy was comparable for both treatments. 5% lidocaine medicated plaster showed a favourable efficacy/safety profile with greater improvements in patient satisfaction and QoL compared with pregabalin for both indications, supporting its first line position in the treatment of localized neuropathic pain.

Efficacy and safety of combination therapy with 5% lidocaine medicated plaster and pregabalin in post-herpetic neuralgia and diabetic polyneuropathy

OBJECTIVE

Neuropathic pain is often difficult to treat due to a complex pathophysiology. This study evaluated the efficacy, tolerability and safety of combination therapy with 5% lidocaine medicated plaster and pregabalin for neuropathic pain in patients with post-herpetic neuralgia (PHN) or painful diabetic polyneuropathy (DPN).

METHODS

Patients completing 4-week monotherapy with 5% lidocaine medicated plaster or pregabalin were enrolled in an 8-week combination phase. Patients with adequate response to monotherapy (recalled average pain intensity of 4 or less on 11-point numeric rating scale in the previous 3 days [NRS-3 score]) continued their previous therapy, whereas those with insufficient response received combination therapy. Efficacy endpoints included change in NRS-3 from combination phase baseline, Patient and Clinical Global Impression of Change (PGIC/CGIC), and patient's satisfaction with treatment. Safety evaluation included adverse events (AEs), drug-related AEs (DRAEs), and withdrawal due to AEs.

CLINICAL TRIAL REGISTRATION

EudraCT No. 2006-003132-29.

RESULTS

Of 229 patients in the per-protocol set (PPS: 68 PHN and 161 DPN), 71 received 5% lidocaine medicated plaster monotherapy, 57 had pregabalin added to 5% lidocaine medicated plaster, 57 pregabalin monotherapy and 44 received 5% lidocaine medicated plaster in addition to continued pregabalin treatment. There were no meaningful differences in demographic data between the treatment groups. Patients continuing on monotherapy demonstrated additional decreases in NRS-3 scores. Patients receiving combination therapy achieved clinically relevant reduction in NRS-3 values in addition to improvement achieved during the 4 weeks of monotherapy. Improvement was similar between the two combination therapy groups. Considerable improvements in patients' treatment satisfaction were reported. Incidences of AEs were in line with previous reports for the two treatments and combination therapy was generally well tolerated.

CONCLUSIONS

In patients with PHN and painful DPN failing to respond to monotherapy, combination therapy with 5% lidocaine medicated plaster and pregabalin provides additional clinically relevant pain relief and is safe and well-tolerated.

Laser-evoked potentials as a tool for assessing the efficacy of antinociceptive drugs

Laser-evoked potentials (LEPs) are brain responses to laser radiant heat pulses and reflect the activation of Adelta nociceptors. LEPs are to date the reference standard technique for studying nociceptive pathway function in patients with neuropathic pain. To find out whether LEPs also provide a useful neurophysiological tool for assessing antinociceptive drug efficacy, in this double-blind placebo-controlled study we measured changes induced by the analgesic tramadol on LEPs in 12 healthy subjects. We found that tramadol decreased the amplitude of LEPs, whereas placebo left LEPs unchanged. The opioid antagonist naloxone partially reversed the tramadol-induced LEP amplitude decrease. We conclude that LEPs may be reliably used in clinical practice and research for assessing the efficacy of antinociceptive drugs.

Efficacy and safety of 5% lidocaine (lignocaine) medicated plaster in comparison with pregabalin in patients with postherpetic neuralgia and diabetic polyneuropathy: interim analysis from an open-label, two-stage adaptive, randomized, controlled trial

BACKGROUND AND OBJECTIVE

Postherpetic neuralgia (PHN) and diabetic polyneuropathy (DPN) are two common causes of peripheral neuropathic pain. Typical localized symptoms can include burning sensations or intermittent shooting or stabbing pains with or without allodynia. Evidence-based treatment guidelines recommend the 5% lidocaine (lignocaine) medicated plaster or pregabalin as first-line therapy for relief of peripheral neuropathic pain. This study aimed to compare 5% lidocaine medicated plaster treatment with pregabalin in patients with PHN and patients with DPN.

METHODS

The study was a two-stage, adaptive, randomized, controlled, open-label, multicentre trial that incorporated a drug wash-out phase of up to 2 weeks prior to the start of the comparative phase. At the end of the enrollment phase, patients who fulfilled the eligibility criteria were randomized to either 5% lidocaine medicated plaster or pregabalin treatment and entered the 4-week comparative phase. The interim analysis represents the first stage of the two-stage adaptive trial design and was planned to include data from the comparative phase for the first 150 randomized patients of the 300 total planned for the trial. Patients aged > or = 18 years with PHN or DPN were recruited from 53 investigational centres in 14 European countries. For this interim analysis, 55 patients with PHN and 91 with DPN (full-analysis set [FAS]), randomly assigned to the treatment groups, were available for analysis. Topical 5% lidocaine medicated plaster treatment was administered by patients to the area of most painful skin. A maximum of three or four plasters were applied for up to 12 hours within each 24-hour period in patients with PHN or DPN, respectively. Pregabalin capsules were administered orally, twice daily. The dose was titrated to effect: all patients received 150 mg/day in the first week and 300 mg/day in the second week of treatment. After 1 week at 300 mg/day, the dose of pregabalin was further increased to 600 mg/day in patients with high pain intensity scores. The pre-planned primary study endpoint was the rate of treatment responders, defined as completing patients experiencing a reduction from baseline of > or = 2 points or an absolute value of < or = 4 points on the 11-item numerical rating scale of recalled average pain intensity over the last 3 days (NRS-3), after 4 weeks of treatment. Secondary endpoints included > or = 30% and > or = 50% reductions in NRS-3 scores, changes in neuropathic pain symptom inventory (NPSI) scores and allodynia severity ratings. Overall, 65.3% of patients treated with the 5% lidocaine medicated plaster and 62.0% receiving pregabalin responded to treatment with respect to the primary endpoint. A higher proportion of PHN patients responded to plaster treatment compared with pregabalin (63.0% vs 37.5%), whereas in the larger DPN group treatments were comparable. Both treatments improved NPSI scores and reduced allodynia severity. Patients administering lidocaine plaster experienced fewer drug-related adverse events (3.9% vs 39.2%) and there were substantially fewer discontinuations due to drug-related adverse events (1.3% vs 20.3%).

CONCLUSION

After 4 weeks, 5% lidocaine medicated plaster treatment was associated with similar levels of analgesia in patients with PHN or DPN but substantially fewer frequent adverse events than pregabalin.

Tools for assessing neuropathic pain

Giorgio Cruccu and Andrea Truini discuss a new pain assessment tool published in PLoS Medicine called Standardized Evaluation of Pain and they review other tools to assess neuropathic pain.

Development and initial validation of an expanded and revised version of the Short-form McGill Pain Questionnaire (SF-MPQ-2)

The objective of the present research was to develop a single measure of the major symptoms of both neuropathic and non-neuropathic pain that can be used in studies of epidemiology, natural history, pathophysiologic mechanisms, and treatment response. We expanded and revised the Short-form McGill Pain Questionnaire (SF-MPQ) pain descriptors by adding symptoms relevant to neuropathic pain and by modifying the response format to a 0-10 numerical rating scale to provide increased responsiveness in longitudinal studies and clinical trials. The reliability, validity, and subscale structure of the revised SF-MPQ (SF-MPQ-2) were examined in responses from 882 individuals with diverse chronic pain syndromes and in 226 patients with painful diabetic peripheral neuropathy who participated in a randomized clinical trial. The data suggest that the SF-MPQ-2 has excellent reliability and validity, and the results of both exploratory and confirmatory factor analyses provided support for four readily interpretable subscales-continuous pain, intermittent pain, predominantly neuropathic pain, and affective descriptors. These results provide a basis for use of the SF-MPQ-2 in future clinical research, including clinical trials of treatments for neuropathic and non-neuropathic pain conditions.

Laser evoked potential recording from intracerebral deep electrodes

OBJECTIVE

To investigate whether recording from deep intracerebral (IC) electrodes can disclose laser evoked potential (LEP) components generated under the cerebral cortex.

METHODS

LEPs were recorded to hand and/or perioral region stimulation from 7 patients suffering from Parkinson's disease, who underwent implant of IC electrodes in the globus pallidum pars interna (GPi), in the subthalamic nucleus (STN) and in the pedunculopontine nucleus (PPN). LEPs were obtained from the IC electrode contacts and from the Cz vertex, referred to the nose.

RESULTS

The scalp traces showed a triphasic response (P1-N2-P2). The IC electrodes recorded two main components (ICP2 and ICN2), showing the same latencies as the scalp N2 and P2 potentials, respectively. The ICP2-ICN2 complex was sometimes preceded by a ICP1 wave at the same latency of the scalp P1 response.

CONCLUSIONS

The LEP components recorded from the IC electrodes mirrored the ones picked up from the Cz lead, thus suggesting that they are probably generated by the opposite pole of the same cortical sources producing the scalp responses.

SIGNIFICANCE

In the IC traces, there was no evidence of earlier potentials possibly generated within the thalamus or of subcortical far-field responses. This means that the nociceptive signal amplification occurring within the cerebral cortex is necessary to produce identifiable LEP components.

Persistent pain after groin hernia surgery: a qualitative analysis of pain and its consequences for quality of life

BACKGROUND

Despite a high prevalence of persistent groin pain after hernia repair, the specific nature of the pain and its clinical manifestation are poorly known. The aim of this study was to determine the type of post-herniorrhaphy pain and its influence on daily life.

METHODS

In order to assess long-term pain qualitatively and to explore how it affects quality of life, 100 individuals with persisting pain, identified in a cohort study of patients operated for groin hernia, were neurologically examined, along with 100 pain-free controls matched for age, gender and type of operation. The patients were asked to answer the SF-36 questionnaire, the hospital anxiety and depression scale, the Swedish Scales of Personality (SSP) and a standardised questionnaire for assessing everyday life coping. The patients were approached approximately 4.9 years after surgery.

RESULTS

Twenty-two patients from the pain group had become pain free by the time of examination, whereas 76 patients still had pain, of whom 47 (68%) suffered from neuropathic pain and 11 from nociceptive pain. The remaining patients suffered from mixed pain, neuropathic and nociceptive, or were found to have another reason for pain. All dimensions of SF-36 were poorer for the pain group than the control group.

CONCLUSION

Persistent post-herniorrhaphy pain is mainly neuropathic and has a substantial impact on health-related quality of life.

Development and preliminary validation of the NePIQoL: a quality-of-life measure for neuropathic pain

Neuropathic pain is frequently associated with negative effects on quality of life (QoL), affecting physical, social, and psychological functioning. Of many existing scales used to measure QoL, none have been validated in a neuropathic pain patient population. This study reports on the development and preliminary psychometric evaluation of the Neuropathic Pain Impact on Quality-of-Life questionnaire (NePIQoL), a measure to assess QoL in neuropathic pain. In Phase I, focus groups with 27 patients and a panel of experts identified QoL issues for inclusion in the measure. Initial items (152) and response categories were pretested using cognitive interviewing (18 patients). Following this, the number of items was reduced to 91. In Phase II, the 91-item version of the NePIQoL was administered to a further 112 patients, poorly performing items were identified, and internal consistency was examined. In Phase III, the revised NePIQoL was administered to a further 110 patients on two occasions to examine validity and test-retest reliability. Qualitative and quantitative pretesting led to extensive revision, resulting in a final measure of 42 items. Finally, Phase IV tested the concurrent validity and responsiveness of the NePIQoL. The authors conclude that the NePIQoL is an acceptable, patient-derived, neuropathic pain-specific measure with evidence of reliability, validity, and temporal stability.

Trigeminal neuralgia and pain related to multiple sclerosis

Although many patients with multiple sclerosis (MS) complain of trigeminal neuralgia (TN), its cause and mechanisms are still debatable. In a multicentre controlled study, we collected 130 patients with MS: 50 patients with TN, 30 patients with trigeminal sensory disturbances other than TN (ongoing pain, dysaesthesia, or hypoesthesia), and 50 control patients. All patients underwent pain assessment, trigeminal reflex testing, and dedicated MRI scans. The MRI scans were imported and normalised into a voxel-based, 3D brainstem model that allows spatial statistical analysis. The onset ages of MS and trigeminal symptoms were significantly older in the TN group. The frequency histogram of onset age for the TN group showed that many patients fell in the age range of classic TN. Most patients in TN and non-TN groups had abnormal trigeminal reflexes. In the TN group, 3D brainstem analysis showed an area of strong probability of lesion (P<0.0001) centred on the intrapontine trigeminal primary afferents. In the non-TN group, brainstem lesions were more scattered, with the highest probability for lesions (P<0.001) in a region involving the subnucleus oralis of the spinal trigeminal complex. We conclude that the most likely cause of MS-related TN is a pontine plaque damaging the primary afferents. Nevertheless, in some patients a neurovascular contact may act as a concurring mechanism. The other sensory disturbances, including ongoing pain and dysaesthesia, may arise from damage to the second-order neurons in the spinal trigeminal complex.

Laser evoked potentials in carpal tunnel syndrome

OBJECTIVES

The aim of this study was to evaluate the function of Adelta fibers at the hand level in patients with clinical symptoms of Carpal Tunnel Syndrome (CTS) using CO(2) laser evoked potentials (LEPs), in light of the intensity and distribution of sensory symptoms and pain.

METHODS

Thirty-four CTS outpatients (62 hands) were compared to 23 sex- and age-matched control subjects (46 hands). The periungueal skin of the first, second, third and fifth fingers, and the dorsum of the hands were stimulated in random order. The latency and amplitude of the N2, P2 and N1 components were evaluated with respect to the Nerve Conduction Study (NCS) data, clinical scales, pain intensity and glove-like symptoms distribution.

RESULTS

The amplitude of the N2-P2 complex was significantly reduced in CTS hands compared to normal hands after stimulation of the second and third fingers, even in patients with mild nerve conduction impairment. No significant fifth finger LEP abnormalities were found in patients with glove-like distribution symptoms. The N2-P2 amplitude at the second and third fingers was positively correlated with the severity of sensory symptoms.

CONCLUSIONS

The involvement of median nerve Adelta fibers in CTS seems to be an early phenomenon, which concurs with the impairment of large motor and sensory afferents and is linked to the severity of the disease.

SIGNIFICANCE

The finding of reduced sensory symptoms in patients with severe thin afferents damage, may suggest a slight expression of central sensitisation phenomena in the advanced stage of CTS syndrome.

Assessment and diagnosis of neuropathic pain

PURPOSE OF REVIEW

Classification of neuropathic pain has been based on disease entities, anatomical localization or histological observations. There is now recognition from clinical investigations that neuropathic pain is not a monolithic entity, but instead presents as a composite of pain and other sensory symptoms.

RECENT FINDINGS

Attempts are underway to supplement the traditional classification with a classification that links pain and sensory symptoms with neurobiological mechanisms. This mechanism or symptom-based classification takes negative and positive sensory symptoms into account. By using a battery of standardized quantitative sensory tests the characteristic profile of sensory symptoms can be elucidated in each patient with a bedside assessment. These procedures can be fostered by apparative neurophysiological analysis, imaging techniques and biopsies. Moreover, in questionnaires verbal descriptors can depict the quality and intensity of the individual pain. They have proven to be sensible screening tools for neuropathic pain components.

SUMMARY

Application of quantitative sensory testing and questionnaires can aid in more versatile descriptions of neuropathic pain symptoms. If it were possible to characterize the concert of the distinct mechanisms and symptoms that operate in one individual patient, an optimal polypharmacotherapy that addresses the specific combinations of mechanisms may be established for each patient.

Subcutaneous Botulinum toxin type A reduces capsaicin-induced trigeminal pain and vasomotor reactions in human skin

The present human study aimed at investigating the effect of subcutaneous administration of Botulinum toxin type A (BoNT/A) on capsaicin-induced trigeminal pain, neurogenic inflammation and experimentally induced cutaneous pain modalities. Fourteen healthy males (26.3+/-2.6 years) were included in this double-blind and placebo-controlled trial. The subjects received subcutaneous BoNT/A (22.5U) and isotonic saline in the mirror sides of their forehead. Pain and neurogenic inflammation was induced by four intradermal injections of capsaicin (100mug/muL) (before, and days 1, 3 and 7 after treatments). The capsaicin-induced pain intensity, pain area, the area of secondary hyperalgesia, the area of visible flare and vasomotor reactions were recorded together with cutaneous heat, electrical and pressure pain thresholds. BoNT/A reduced the capsaicin-induced trigeminal pain intensity compared to saline (F=37.9, P<0.001). The perceived pain area was smaller for the BoNT/A-treated side compared to saline (F=7.8, P<0.05). BoNT/A reduced the capsaicin-induced secondary hyperalgesia (F=5.3, P<0.05) and flare area (F=10.3, P<0.01) compared to saline. BoNT/A reduced blood flow (F(1,26)=109.5, P<0.001) and skin temperature (F(1,26)=63.1, P<0.001) at the capsaicin injection sites compared to saline and its suppressive effect was maximal at days 3 and 7 (P<0.05, post hoc test). BoNT/A elevated cutaneous heat pain thresholds (F=17.1, P<0.001) compared to saline; however, no alteration was recorded for electrical or pressure pain thresholds (P>0.05). Findings from the present study suggest that BoNT/A appears to preferentially target Cfibers and probably TRPV1-receptors, block neurotransmitter release and subsequently reduce pain, neurogenic inflammation and cutaneous heat pain threshold.

Measuring outcomes in adult brachial plexus reconstruction

The focus of this article is on evaluating the various outcome measures of surgical interventions for adult brachial plexus injuries. From a surgeon's perspective, the goals of surgery have largely focused on the return of motor function and restoration of protective sensation. From a patient's perspective, alleviation of pain, cosmesis, return to work, and emotional state are also important. The ideal outcome measure should be valid, reliable, responsive, unbiased, appropriate, and easy. The author outlines pitfalls and benefits of current outcome measures and offers thoughts on possible future measures.

Ketamine as an adjuvant in sympathetic blocks for management of central sensitization following peripheral nerve injury

Proliferation of NMDA receptors and role of glutamate in producing central sensitization and 'wind up' phenomena in CRPS [complex regional pain syndrome] forms a strong basis for the use of Ketamine to block the cellular mechanisms that initiate and maintain these changes. In this case series, we describe 3 patients of CRPS Type II with debilitating central sensitization, heat/mechano allodynia and cognitive symptoms that we termed 'vicarious pain'. Each of these patients had dramatic relief with addition of Ketamine as an adjuvant to the sympathetic blocks after conventional therapy failed.

Case Reports

All 3 patients suffered gunshot wounds and developed characteristic features of CRPS Type II. Within 2–3 weeks they developed extraterritorial symptoms typical of central sensitization. The generalized mechanical allodynia and debilitating heat allodynia described to be rare in human subjects had life altering affect on their daily life. Case 2 and 3 also described an unusual cognitive phenomenon i.e. visual stimuli of friction would evoke severe pain in the affected limb that we have termed as 'vicarious pain'. They responded positively to sympathetic blocks but the sympatholysis did not bring relief to the heat and mechanical allodynia. Addition of Ketamine 0.5 mg/kg to the sympathetic blocks elicited resulted in marked relief in the allodynia.

Conclusion

Ketamine has a special role in patients with debilitating heat allodynia and positive cognitive symptoms via its action on central pain pathway. As an adjuvant in sympatholytic blocks it has a targeted action without significant neuropsychiatric side effects.