Female sex is a risk factor for painful diabetic peripheral neuropathy: the EURODIAB prospective diabetes complications study

AIMS/HYPOTHESIS

While the risk factors for diabetic peripheral neuropathy (DPN) are now well recognised, the risk factors for painful DPN remain unknown. We performed analysis of the EURODIAB Prospective Complications Study data to elucidate the incidence and risk factors of painful DPN.

METHODS

The EURODIAB Prospective Complications Study recruited 3250 participants with type 1 diabetes who were followed up for 7.3±0.6 (mean ± SD) years. To evaluate DPN, a standardised protocol was used, including clinical assessment, quantitative sensory testing and autonomic function tests. Painful DPN (defined as painful neuropathic symptoms in the legs in participants with confirmed DPN) was assessed at baseline and follow-up.

RESULTS

At baseline, 234 (25.2%) out of 927 participants with DPN had painful DPN. At follow-up, incident DPN developed in 276 (23.5%) of 1172 participants. Of these, 41 (14.9%) had incident painful DPN. Most of the participants who developed incident painful DPN were female (73% vs 48% painless DPN p=0.003) and this remained significant after adjustment for duration of diabetes and HbA1c (OR 2.69 [95% CI 1.41, 6.23], p=0.004). The proportion of participants with macro- or microalbuminuria was lower in those with painful DPN compared with painless DPN (15% vs 34%, p=0.02), and this association remained after adjusting for HbA1c, diabetes duration and sex (p=0.03).

CONCLUSIONS/INTERPRETATION

In this first prospective study to investigate the risk factors for painful DPN, we definitively demonstrate that female sex is a risk factor for painful DPN. Additionally, there is less evidence of diabetic nephropathy in incident painful, compared with painless, DPN. Thus, painful DPN is not driven by cardiometabolic factors traditionally associated with microvascular disease. Sex differences may therefore play an important role in the pathophysiology of neuropathic pain in diabetes. Future studies need to look at psychosocial, genetic and other factors in the development of painful DPN.

Pain-motor integration in chronic pain: A neurophysiological study

OBJECTIVE

Chronic pain may lead to functional changes in several brain regions, including the primary motor cortex (M1). Our neurophysiological study aimed to probe M1 plasticity, through a non-invasive transcranial magnetic stimulation protocol, in a cohort of patients with chronic pain.

METHODS

Twenty patients with chronic pain (age ± SD: 62.9 ± 9.9) and 20 age- and sex-matched healthy controls (age ± SD: 59.6 ± 15.8) were recruited. Standardized scales were used for the evaluation of pain severity. Neurophysiological measures included laser-evoked potentials (LEPs) and motor-evoked potentials (MEPs) collected at baseline and over 60 minutes following a standardized Laser-paired associative stimulation (Laser-PAS) protocol.

RESULTS

LEPs and MEPs were comparable in patients with chronic pain and controls. The pain threshold was lower in patients than in controls. Laser-PAS elicited decreased responses in patients with chronic pain. The response to Laser-PAS was similar in subgroups of patients with different chronic pain phenotypes.

CONCLUSIONS

M1 plasticity, as tested by Laser-PAS, is altered in patients with chronic pain, possibly reflecting abnormal pain-motor integration processes.

SIGNIFICANCE

Chronic pain is associated with a disorder of M1 plasticity raising from abnormal pain-motor integration.

Considerations When Using Gabapentinoids to Treat Trigeminal Neuralgia: A Review

Despite the exemplary efficacy of voltage-gated sodium channel blockers as a first-line treatment of trigeminal neuralgia, the pharmacological management of this excruciating facial pain condition remains a major issue, as these first-line drugs produce intolerable side effects in a significant portion of patients. In addition, in patients with concomitant continuous pain, the efficacy of these drugs may drop, thus suggesting the opportunity to test the efficacy of different drug categories. The aim of this review is to provide current, evidence-based, knowledge about the use of gabapentin and other α2δ ligands in patients with trigeminal neuralgia. We searched for relevant papers within PubMed, EMBASE, the Cochrane Database of Systematic Reviews and the Clinical Trials database (ClinicalTrials.gov), considering publications up to April 2023. Two authors independently selected studies for inclusion and data extraction. The efficacy of α2δ ligands, gabapentin and pregabalin, has been assessed in seven controlled or open-label studies. Despite the low quality of evidence, the favorable tolerability profile and the possible action on concomitant continuous pain make this drug category of interest for future trials in trigeminal neuralgia.

Joint European Academy of Neurology-European Pain Federation-Neuropathic Pain Special Interest Group of the International Association for the Study of Pain guidelines on neuropathic pain assessment

BACKGROUND AND PURPOSE

In these guidelines, we aimed to develop evidence-based recommendations for the use of screening questionnaires and diagnostic tests in patients with neuropathic pain (NeP).

METHODS

We systematically reviewed studies providing information on the sensitivity and specificity of screening questionnaires, and quantitative sensory testing, neurophysiology, skin biopsy, and corneal confocal microscopy. We also analysed how functional neuroimaging, peripheral nerve blocks, and genetic testing might provide useful information in diagnosing NeP.

RESULTS

Of the screening questionnaires, Douleur Neuropathique en 4 Questions (DN4), I-DN4 (self-administered DN4), and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) received a strong recommendation, and S-LANSS (self-administered LANSS) and PainDETECT weak recommendations for their use in the diagnostic pathway for patients with possible NeP. We devised a strong recommendation for the use of skin biopsy and a weak recommendation for quantitative sensory testing and nociceptive evoked potentials in the NeP diagnosis. Trigeminal reflex testing received a strong recommendation in diagnosing secondary trigeminal neuralgia. Although many studies support the usefulness of corneal confocal microscopy in diagnosing peripheral neuropathy, no study specifically investigated the diagnostic accuracy of this technique in patients with NeP. Functional neuroimaging and peripheral nerve blocks are helpful in disclosing pathophysiology and/or predicting outcomes, but current literature does not support their use for diagnosing NeP. Genetic testing may be considered at specialist centres, in selected cases.

CONCLUSIONS

These recommendations provide evidence-based clinical practice guidelines for NeP diagnosis. Due to the poor-to-moderate quality of evidence identified by this review, future large-scale, well-designed, multicentre studies assessing the accuracy of diagnostic tests for NeP are needed.

A TRPM7 mutation linked to familial trigeminal neuralgia: Omega current and hyperexcitability of trigeminal ganglion neurons

Trigeminal neuralgia (TN) is a unique pain disorder characterized by intense paroxysmal facial pain within areas innervated by the trigeminal nerve. Although most cases of TN are sporadic, familial clusters of TN suggest that genetic factors may contribute to this disorder. Whole-exome sequencing in patients with TN reporting positive family history demonstrated a spectrum of variants of ion channels including TRP channels. Here, we used patch-clamp analysis and Ca²⁺ and Na⁺ imaging to assess a rare variant in the TRPM7 channel, p.Ala931Thr, within transmembrane domain 3, identified in a man suffering from unilateral TN. We showed that A931T produced an abnormal inward current carried by Na⁺ and insensitive to the pore blocker Gd³⁺. Hypothesizing that replacement of the hydrophobic alanine at position 931 with the more polar threonine destabilizes a hydrophobic ring, near the voltage sensor domain, we performed alanine substitutions of F971 and W972 and obtained results suggesting a role of A931-W972 hydrophobic interaction in S3-S4 hydrophobic cleft stability. Finally, we transfected trigeminal ganglion neurons with A931T channels and observed that expression of this TRPM7 variant lowers current threshold and resting membrane potential, and increases evoked firing activity in TG neurons. Our results support the notion that the TRPM7-A931T mutation located in the S3 segment at the interface with the transmembrane region S4, generates an omega current that carries Na⁺ influx in physiological conditions. A931T produces hyperexcitability and a sustained Na⁺ influx in trigeminal ganglion neurons that may underlie pain in this kindred with trigeminal neuralgia.

Dissecting pain processing in adolescents with Non-Suicidal Self Injury: Could suicide risk lurk among the electrodes?

Background

Although non‐suicidal self‐injury (NSSI) disorder is highly prevalent in adolescents, its relationship with pain system function and suicidality is still controversial. The present study was designed to assess the function of the nociceptive afferent pathways and the endogenous pain modulation in adolescent patients with NSSI and to longitudinally register any suicide attempt, describe its frequency and find a possible association between suicide, neurophysiological measures and psychological measures.

Methods

We enrolled 30 adolescents suffering from NSSI and 20 age‐ and gender‐matched healthy controls. Patients underwent a comprehensive psychological evaluation. Each participant underwent thermal pain thresholds of the quantitative sensory testing, laser‐evoked potential recording to study the ascending nociceptive pathway and the conditioned pain modulation testing to test the endogenous pain modulation.

Results

We found that patients with NSSI had a reduced amplitude of the N2 component of laser‐evoked potentials and an abnormal conditioned pain modulation. The amplitude of the N2 was associated with suicidal risk.

Conclusions

The deficit of the endogenous pain modulation likely depends on a saturation due to continuous pain solicitation. The strong association of a reduced amplitude of the N2 component with suicide suggests that it may serve as a possible biomarker in self‐harming adolescents.

Significance

The present study identifies the N2 component of laser‐evoked potentials as a possible neurophysiological biomarker of suicidal risk in patients with non‐suicidal self‐injury, therefore, raising the possibility for a non‐invasive test to identify subjects at higher risk of suicide among self‐harming patients.

Pain due to Ehlers-Danlos Syndrome Is Associated with Deficit of the Endogenous Pain Inhibitory Control

OBJECTIVES

Although pain is a common complication of the hypermobile type of Ehlers-Danlos syndrome, its underlying mechanisms are still an issue of controversy. In this psychophysical study, we aimed at testing small-fiber function and the endogenous pain inhibitory control in patients with pain due to Ehlers-Danlos syndrome.

METHODS

In 22 patients with pain due to Ehlers-Danlos syndrome and 22 healthy participants, matched for age and sex, we tested small-fiber function using quantitative sensory testing and the endogenous pain inhibitory control using the conditioned pain modulation (CPM) protocol. As quantitative sensory testing methods, we included thermal pain and mechanical pain thresholds and the wind-up ratio. The CPM protocol consisted of two heat painful stimuli, that is, a test stimulus and a conditioning stimulus.

RESULTS

All patients complained of widespread pain. Quantitative sensory testing revealed no small-fiber deficit; in the area of maximum pain, we found an increased wind-up ratio. Whereas in the healthy participants the CPM protocol showed that the test stimulus rating was significantly reduced during conditioning, in patients with pain due to hEDS, the test stimulus rating increased during conditioning.

CONCLUSIONS

Our psychophysical study showing that patients with pain due to hEDS have an increased wind-up ratio in the area of maximum pain and abnormal CPM protocol suggests that in this condition, pain is associated with central sensitization, possibly due to deficit of the endogenous pain inhibitory control. These data might be relevant to pharmacological treatment.

N-Acetylcysteine causes analgesia in a mouse model of painful diabetic neuropathy

N-Acetylcysteine, one of the most prescribed antioxidant drugs, enhances pain threshold in rodents and humans by activating mGlu2 metabotropic glutamate receptors. Here, we assessed the analgesic activity of N-acetylcysteine in the streptozotocin model of painful diabetic neuropathy and examined the effect of N-acetylcysteine on proteins that are involved in mechanisms of nociceptive sensitization. Mice with blood glucose levels ≥250 mg/dl in response to a single intraperitoneal (i.p.) injection of streptozotocin (200 mg/kg) were used for the assessment of mechanical pain thresholds. Systemic treatment with N-acetylcysteine (100 mg/kg, i.p., either single injection or daily injections for seven days) caused analgesia in diabetic mice. N-acetylcysteine-induced analgesia was abrogated by the Sxc− inhibitors, sulfasalazine (8 mg/kg, i.p.), erastin (30 mg/kg, i.p.), and sorafenib (10 mg/kg, i.p.), or by the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.). Repeated administrations of N-acetylcysteine in diabetic mice reduced ERK1/2 phosphorylation in the dorsal region of the lumbar spinal cord. The analgesic activity of N-acetylcysteine was occluded by the MEK inhibitor, PD0325901 (25 mg/kg, i.p.), the TRPV1 channel blocker, capsazepine (40 mg/kg, i.p.), or by a cocktail of NMDA and mGlu5 metabotropic glutamate receptor antagonists (memantine, 25 mg/kg, plus MTEP, 5 mg/kg, both i.p.). These findings offer the first demonstration that N-acetylcysteine relieves pain associated with diabetic neuropathy and holds promise for the use of N-acetylcysteine as an add-on drug in diabetic patients.

Real-world effectiveness and tolerability of carbamazepine and oxcarbazepine in 354 patients with trigeminal neuralgia

BACKGROUND

It is widely agreed that carbamazepine and oxcarbazepine are highly effective in the long-term treatment of trigeminal neuralgia. However, the tolerability of these drugs across the different aetiologies of trigeminal neuralgia is still undetermined.

METHODS

In this retrospective, real-world study, we assessed the effectiveness and tolerability of carbamazepine and oxcarbazepine in a large cohort of patients with classical (254 patients), secondary (60 patients) and idiopathic (40 patients) trigeminal neuralgia. We analysed data using a propensity score analysis to account for selection bias; frequencies of side effects associated with carbamazepine and oxcarbazepine were calculated by adjusting data with the inverse probability of treatment weighting.

RESULTS

The initial proportion of responders was 88.3% with carbamazepine, and 90.9% with oxcarbazepine. The number of refractory patients was significantly higher in idiopathic (15%) and secondary forms (27%) than in classical trigeminal neuralgia (6%; p < .05). In 53 patients treated with carbamazepine (29.6%) and in 22 treated with oxcarbazepine (12.6%), major side effects caused treatment interruption or dosage reduction to an unsatisfactory level. Side effects occurred more frequently in patients treated with carbamazepine (43.6%) than with oxcarbazepine (30.3%, p < .0001). The frequency of treatment discontinuation was higher in patients with secondary and idiopathic forms than in those with classical trigeminal neuralgia (p < .05).

CONCLUSIONS

Our real-world study shows that carbamazepine and oxcarbazepine are effective in most patients with trigeminal neuralgia; nevertheless, side effects are still a major issue, particularly in patients with secondary and idiopathic trigeminal neuralgia.

SIGNIFICANCE

Although carbamazepine and oxcarbazepine are effective in most patients with trigeminal neuralgia, their side effects are still a major issue, thus necessitating the development of better-tolerated drugs.

Trigeminal Neuralgia TRPM8 Mutation: Enhanced Activation, Basal [Ca2+]i and Menthol Response

Objective

To assess the functional effects of a variant, c.89 G > A (p.Arg30Gln), in the transient receptor potential melastatin 8 (TRPM8) cold-sensing, nonselective cation channel, which we have previously identified in a patient with familial trigeminal neuralgia.

Methods

We carried out Ca²⁺ imaging and whole-cell patch-clamp recording.

Results

The TRPM8 mutation enhances channel activation, increases basal current amplitude and intracellular [Ca²⁺] in cells carrying the mutant channel, and enhances the response to menthol.

Conclusions

We propose that Arg30Gln confers gain-of-function attributes on TRPM8, which contribute to pathogenesis of trigeminal neuralgia in patients carrying this mutation.

Painful stimulation increases spontaneous blink rate in healthy subjects

Spontaneous blink rate is considered a biomarker of central dopaminergic activity. Recent evidence suggests that the central dopaminergic system plays a role in nociception. In the present study, we aimed to investigate whether pain modulates spontaneous blink rate in healthy subjects. We enrolled 15 participants. Spontaneous blink rate was quantified with an optoelectronic system before and after: (1) a painful laser stimulation, and (2) an acoustic startling stimulation. In control experiments, we investigated whether laser stimulation effects depended on stimulation intensity and whether laser stimulation induced any changes in the blink reflex recovery cycle. Finally, we investigated any relationship between spontaneous blink rate modification and pain modulation effect during the cold pressor test. Laser, but not acoustic, stimulation increased spontaneous blink rate. This effect was independent of stimulation intensity and negatively correlated with pain perception. No changes in trigeminal-facial reflex circuit excitability were elicited by laser stimulation. The cold pressor test also induced an increased spontaneous blink rate. Our study provides evidence on the role of dopamine in nociception and suggests that dopaminergic activity may be involved in pain modulation. These findings lay the groundwork for further investigations in patients with pathological conditions characterized by dopaminergic deficit and pain.

Differential involvement of myelinated and unmyelinated nerve fibers in painful diabetic polyneuropathy

BACKGROUND

We aimed at evaluating the differential involvement of large myelinated Aβ-, small myelinated Aδ-, and unmyelinated C-fibers in patients with diabetic polyneuropathy and how they contribute to neuropathic pain.

METHODS

We collected clinical and diagnostic test variables in 133 consecutive patients with diabetic polyneuropathy. All patients underwent Aβ-fiber mediated nerve conduction study, Aδ-fiber mediated laser-evoked potentials and skin biopsy mainly assessing unmyelinated C-fibers.

RESULTS

Pure large-fiber and small-fiber polyneuropathy were relatively uncommon; conversely mixed-fiber polyneuropathy was the most common type of diabetic polyneuropathy (74%). The frequency of neuropathic pain was similar in the three different polyneuropathies. Ongoing burning pain and dynamic mechanical allodynia were similarly associated with specific small-fiber related variables.

CONCLUSIONS

Diabetic polyneuropathy mainly manifests as a mixed-fiber polyneuropathy, simultaneously involving Aβ-, Aδ-, and C-fibers. In most patients, neuropathic pain is distinctly associated with small-fiber damage. The evidence that the frequency of neuropathic pain does not differ across pure large-, pure small-, and mixed-fiber polyneuropathy, raises the possibility that in patients with pure large-fiber polyneuropathy nociceptive nerve terminal involvement might be undetected by standard diagnostic techniques.

Advances in diagnosis, classification, pathophysiology, and management of trigeminal neuralgia

Trigeminal neuralgia is a very painful neurological condition with severe, stimulus-evoked, short-lasting stabbing pain attacks in the face. The past decade has offered new insights into trigeminal neuralgia symptomatology, pathophysiology, and treatment, leading to a change in the classification of the condition. An accurate diagnosis is crucial because neuroimaging interpretation and clinical management differ among the various forms of facial pain. MRI using specific sequences should be a part of the diagnostic workup to detect a possible neurovascular contact and exclude secondary causes. Demonstration of a neurovascular contact should not be used to confirm a diagnosis but rather to facilitate surgical decision making. Carbamazepine and oxcarbazepine are drugs of first choice for long-term treatment, whereas microvascular decompression is the first-line surgery in medically refractory patients. Advances in neuroimaging techniques and animal models will provide further insight into the causes of trigeminal neuralgia and its pathophysiology. Development of more efficacious treatment options is highly warranted.

Concomitant continuous pain in patients with trigeminal neuralgia is associated with trigeminal nerve root atrophy

Introduction

Trigeminal neuralgia is an exemplary neuropathic pain condition characterized by paroxysmal electric-shock-like pain. However, up to 50% of patients also experiences concomitant continuous pain. In this neuroimaging study, we aimed to identify the specific anatomical features of trigeminal nerve root in patients with concomitant continuous pain.

Methods

We enrolled 73 patients with a definitive diagnosis of classical and idiopathic trigeminal neuralgia and 40 healthy participants. The diagnosis of trigeminal neuralgia was independently confirmed by two clinicians. Patients were grouped as patients with purely paroxysmal pain (45 patients) and patients also with concomitant continuous pain (28 patients). All participants underwent a structured clinical examination and a 3T MRI with sequences dedicated to the anatomical study of the trigeminal nerve root, including volumetric study. Images analysis was independently performed by two investigators, blinded to any clinical data.

Results

In most patients with concomitant continuous pain, this type of pain, described as burning, throbbing or aching, manifested at the disease onset. Demographic and clinical variables did not differ between the two groups of patients; the frequency of neurovascular compression and nerve dislocation were similar. Conversely, trigeminal nerve root atrophy was more severe in patients with concomitant continuous pain than in those with purely paroxysmal pain ( p = 0.006).

Conclusions

Our clinical and neuroimaging study found that in patients with trigeminal neuralgia, concomitant continuous pain was associated with trigeminal nerve root atrophy, therefore suggesting that this type of pain is likely related to axonal loss and abnormal activity in denervated trigeminal second-order neurons.

Conduction velocity of the cold spinal pathway in healthy humans

OBJECTIVES

We aimed to investigate the conduction velocity of the cold spinal pathway in healthy humans.

METHODS

Using a cold stimulator consisting of micro-Peltier elements that was able to produce steep cooling ramps up to -300°C/s, we recorded cold-evoked potentials after stimulation of the dorsal midline at C5, T2, T6 and T10 vertebral levels and calculated the conduction velocity of the cold spinal pathway. In all participants, we used laser stimulation to deliver painful heat (Aδ-fibres-mediated) and warm (C-fibres-mediated) stimuli to the same sites in order to compare the conduction velocity of the cold spinal pathway with that of the nociceptive and warm spinal pathways.

RESULTS

Cold stimulation evoked large-amplitude vertex potentials from all stimulation sites. The mean conduction velocity of the cold spinal pathway was 12.0 m/s, which did not differ from that of the nociceptive spinal pathway (10.5 m/s). The mean conduction velocity of the warm spinal pathway was 2.0 m/s.

DISCUSSION

This study provides previously unreported findings regarding cold spinal pathway conduction velocity in humans that may be useful in the assessment of spinal cord lesions as well as in intraoperative monitoring during spinal surgery.

SIGNIFICANCE

This neurophysiological study provides previously unreported findings on cold spinal pathway conduction velocity in healthy humans. Cold-evoked potentials may represent an alternative to laser-evoked potential recording, useful to assess spinothalamic tract in patients with spinal cord lesions and monitor patients during spinal surgery.

Familial trigeminal neuralgia - a systematic clinical study with a genomic screen of the neuronal electrogenisome

Objective

This cross-sectional study examined, for the first time, a large cohort of patients with trigeminal neuralgia, to ascertain the occurrence of familial cases, providing a systematic description of clinical features of familial disease. Since there is evidence linking hyperexcitability of trigeminal ganglion neurons to trigeminal neuralgia, we also carried out an exploratory genetic analysis of the neuronal electrogenisome in these patients.

Methods

We recorded familial occurrence by systematically interviewing all patients with a definite diagnosis of classical or idiopathic trigeminal neuralgia. We found 12 occurrences of trigeminal neuralgia with positive family history out of 88 enrolled patients. Whole-exome sequencing was carried out in 11 patients. We concentrated on the genetic variants within a 173-gene panel, comprising channel genes encoding sodium, potassium, calcium, chloride, transient receptor potential channels, and gap junction channels. Gene expression profiles were based on published RNA sequencing datasets of rodent/human trigeminal ganglia tissues, with a focus on genes related to neuronal excitability.

Results

In patients with familial trigeminal neuralgia, pain was more often located in the right, second division. All patients reported triggers. Four patients experienced concomitant continuous pain. Whole-exome sequencing analysis within the trigeminal ganglion electrogenisome identified 41 rare variants in ion channels, consisting of variants in sodium channels (6), potassium channels (10), chloride channels (5), calcium channels (7), transient receptor potential channels (12), and gap junction channels (1). In one patient, a previously profiled gain-of-function mutation in SCN10A (Nav1.8 p.Ala1304Thr), previously reported in painful neuropathy, was found; this variant was not present in unaffected siblings.

Conclusions

Our results suggest that familial occurrence of trigeminal neuralgia is more common than previously considered. Although our results demonstrate variants in genes encoding voltage-gated ion channels and transient receptor potential channels within these patients, further study will be needed to determine their roles in the pathogenesis of trigeminal neuralgia.

Efficacy and Safety of Low Doses of Trazodone in Patients Affected by Painful Diabetic Neuropathy and Treated with Gabapentin: A Randomized Controlled Pilot Study

BACKGROUND

Painful diabetic neuropathy is an important therapeutic challenge as the efficacy of analgesic drugs in this setting is still unsatisfactory. Monotherapy with available treatments is often not sufficient and a combination of drugs is necessary. Trazodone (TRZ) is a compound with a multi-modal mechanism of action, being a serotonin-2 antagonist/reuptake inhibitor developed and approved for the treatment of depression in several countries. Previous clinical trials suggest a possible beneficial effect of low doses of trazodone for the treatment of patients affected by painful diabetic neuropathy.

OBJECTIVE

This phase II study was designed to collect data on the efficacy and safety of low doses of TRZ combined with gabapentin after 8 weeks of treatment in patients affected by painful diabetic neuropathy.

METHODS

This was a randomized, double-blind, placebo-controlled, multi-center, international, prospective study. Male and female diabetic patients aged 18-75 years and affected by painful diabetic neuropathy were eligible for enrollment. Subjects were randomized (1:1:1 ratio) to TRZ30 (10 mg three times daily for 8 weeks) or TRZ60 (20 mg three times daily for 8 weeks) or placebo. Gabapentin as background therapy was administered in open-label conditions to all patients. The primary endpoint was the change from baseline of the Brief Pain Inventory Short Form item 5 to week 8. Secondary endpoints included the other Brief Pain Inventory Short Form items, and the assessment of anxiety, sleep, quality of life, patient's improvement, and safety.

RESULTS

One hundred and forty-one patients were included in the intention-to-treat population: 43 allocated to the TRZ30 group, 50 to the TRZ60 group, and 48 to the placebo group. After 8 weeks, the mean changes of Brief Pain Inventory Short Form item 5 from baseline were - 3.1, - 2.6, and - 2.5 in the TRZ30, TRZ60, and placebo groups, respectively. No statistically significant differences between groups were seen. Nevertheless, a better trend was observed for TRZ30 vs placebo (95% confidence interval - 1.30, 0.15; p = 0.1179), on top of the background effect of gabapentin administered to all study groups. 62.8% of patients achieved a ≥ 50% reduction in the TRZ30 group, 54% in the TRZ60 group, and 45.8% in the placebo group. At the same time, a statistically significant improvement was observed in Brief Pain Inventory Short Form item 6 for TRZ30 vs placebo (95% confidence interval - 1.54, - 0.07; p = 0.0314). No serious adverse event occurred during the trial and the most frequent treatment-emergent adverse events involved nervous system, QT prolongation, and gastrointestinal disorders.

CONCLUSIONS

All treatment groups showed a clinically meaningful pain improvement; nevertheless, patients in the TRZ30 treatment group reported better efficacy outcomes. This finding suggests that low doses of TRZ could be useful for treating painful diabetic neuropathy, and support further adequately powered confirmatory trials investigating the efficacy of TRZ.

CLINICAL TRIAL REGISTRATION

NCT03202979, date of registration: 29/06/2017.

Acetyl-L-carnitine in painful peripheral neuropathy: a systematic review

Acetyl-L-carnitine (ALC) has shown a neuroprotective effect in patients with peripheral neuropathies of different etiologies. Preclinical studies demonstrated a central anti-nociceptive action, both in neuropathic and nociceptive pain models. The present review aims to provide the knowledge on the efficacy of ALC in patients with painful peripheral neuropathy, based on the evidence. Consistent with the PRISMA statement, authors searched PubMed, Embase and the Cochrane Database of Systematic Reviews for relevant papers, including those issued before April 2018. Two authors independently selected studies for inclusion and data extraction: only trials including patients with a diagnosis of peripheral neuropathy and involving at least 10 patients were considered for the purposes of this review. Fourteen clinical trials were revised, to provide the level of evidence for neuropathy. To assess the global efficacy of ALC in painful peripheral neuropathy, a meta-analysis of four randomized controlled trials was performed. Mean difference in pain reduction as measured on a 10-cm VAS, and 95% CIs were used for pooling continuous data from each trial. Four randomized controlled trials tested ALC in patients with neuropathy secondary to diabetes and to antiretroviral therapy for HIV. Compared to placebo, ALC produced a significant pain reduction equal to 20.2% (95% CI: 8.3%-32.1%, P<0.0001) with respect to baseline. Clinical trials also showed beneficial effects on nerve conduction parameters and nerve fiber regeneration, with a good safety profile. These data indicate that ALC provides an effective and safe treatment in patients with painful peripheral neuropathy. We recommend further studies to assess the optimal dose and duration of the therapeutic effect (also after treatment withdrawal).

A Delphi consensus statement of the Neuropathic Pain Special Interest Group of the Italian Neurological Society on pharmacoresistant neuropathic pain

To improve patient care and help clinical research, the Neuropathic Pain Special Interest Group of the Italian Neurological Society appointed a task force to elaborate a consensus statement on pharmacoresistant neuropathic pain. The task force included 19 experts in neuropathic pain. These experts participated in a Delphi survey consisting of three consecutive rounds of questions and a face-to-face meeting, designed to achieve a consensus definition of pharmacoresistant neuropathic pain. In the three rounds of questions, the participants identified and described the main distinguishing features of pharmacoresistance. In the face-to-face meeting the participants discussed the clinical features determining pharmacoresistance. They finally agreed that neuropathic pain is pharmacoresistant when "the patient does not reach the 50% reduction of pain or an improvement of at least 2 points in the Patient Global Impression of Change, having used all drug classes indicated as first, second, or third line in the most recent and widely agreed international guidelines, for at least 1 month after titration to the highest tolerable dose." Our consensus statement might be useful for identifying eligible patients for invasive treatments, and selecting patients in pharmacological trials, thus improving patient care and helping clinical research.

Micronized Palmitoylethanolamide: A Post Hoc Analysis of a Controlled Study in Patients with Low Back Pain - Sciatica

BACKGROUND

Despite being widely prescribed, relatively few controlled trials have been conducted on the class of neurotrophic/antinociceptive nutraceuticals. While performing a search in the literature, we came across an old registration study on micronized palmitoylethanolamide in patients with low back pain - sciatica by Guida and colleagues.

METHODS

We contacted the authors of the article and obtained all the original material, which allowed us to reanalyze the study. We assessed its clinical relevance by calculating the numbers needed to treat for pain (visual analog scale) and function (Roland-Morris Questionnaire). After excluding patients for whom the information available was insufficient, we assigned each patient to one of the five categories of increasing probability of neuropathic pain: pure lumbago, lumbago with projecting pain to surrounding regions (e.g. gluteus or groin), lumbago with projecting pain to the thigh or leg, pure sciatica and radiculopathy, and investigated any correlations (Spearman) between the improvement in pain and function with these five classes.

RESULTS

Compared with placebo, palmitoylethanolamide 600 mg/die yielded a number needed to treat of 1.7 (95% confidence interval: 1.4-2) for pain, and 1.5 (95% confidence interval: 1.4-1.7) for function. The correlation between the five categories was highly significant for pain relief (P <0.0001), though not significant for reduced dysfunction.

CONCLUSION

Palmitoylethanolamide was extremely effective on pain and function in a large cohort of patients with low back pain - sciatica. Although, the multiple mechanisms of action of palmitoylethanolamide are ideal for mixed pain conditions such as low back pain - sciatica, the correlation between pain relief and the likelihood of neuropathic pain suggests that this drug exerts a predominant action on the neuropathic pain component.

The IASP classification of chronic pain for ICD-11: chronic neuropathic pain

The upcoming 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD) of the World Health Organization (WHO) offers a unique opportunity to improve the representation of painful disorders. For this purpose, the International Association for the Study of Pain (IASP) has convened an interdisciplinary task force of pain specialists. Here, we present the case for a reclassification of nervous system lesions or diseases associated with persistent or recurrent pain for ≥3 months. The new classification lists the most common conditions of peripheral neuropathic pain: trigeminal neuralgia, peripheral nerve injury, painful polyneuropathy, postherpetic neuralgia, and painful radiculopathy. Conditions of central neuropathic pain include pain caused by spinal cord or brain injury, poststroke pain, and pain associated with multiple sclerosis. Diseases not explicitly mentioned in the classification are captured in residual categories of ICD-11. Conditions of chronic neuropathic pain are either insufficiently defined or missing in the current version of the ICD, despite their prevalence and clinical importance. We provide the short definitions of diagnostic entities for which we submitted more detailed content models to the WHO. Definitions and content models were established in collaboration with the Classification Committee of the IASP's Neuropathic Pain Special Interest Group (NeuPSIG). Up to 10% of the general population experience neuropathic pain. The majority of these patients do not receive satisfactory relief with existing treatments. A precise classification of chronic neuropathic pain in ICD-11 is necessary to document this public health need and the therapeutic challenges related to chronic neuropathic pain.

Challenges recruiting to a proof-of-concept pharmaceutical trial for a rare disease: the trigeminal neuralgia experience

Background

This study aimed to describe recruitment challenges encountered during a phase IIa study of vixotrigine, a state and use-dependent Nav1.7 channel blocker, in individuals with trigeminal neuralgia.

Methods

This was an international, multicenter, placebo-controlled, randomized withdrawal study that included a 7-day run-in period, a 21-day open-label phase, and a 28-day double-blind phase in which patients (planned n = 30) were randomized to vixotrigine or placebo. Before recruitment, all antiepileptic drugs had to be stopped, except for gabapentin or pregabalin. After the trial, patients returned to their original medications. Patient recruitment was expanded beyond the original five planned (core) centers in order to meet target enrollment (total recruiting sites N = 25). Core sites contributed data related to patient identification for study participation (prescreening data). Data related to screening failures and study withdrawal were also analyzed using descriptive statistics.

Results

Approximately half (322/636; 50.6%) of the patients who were prescreened at core sites were considered eligible for the study and 56/322 (17.4%) were screened. Of those considered eligible, 26/322 (8.1%) enrolled in the study and 6/322 (1.9%) completed the study. In total, 125 patients were screened across all study sites and 67/125 (53.6%) were enrolled. At prescreening, reasons for noneligibility varied by site and were most commonly diagnosis change (78/314; 24.8%), age > 80 years (75/314; 23.9%), language/distance/mobility (61/314; 19.4%), and noncardiac medical problems (53/314; 16.9%). At screening, frequently cited reasons for noneligibility included failure based on electrocardiogram, insufficient pain, and diagnosis change.

Conclusions

Factors contributing to recruitment challenges encountered in this study included diagnosis changes, anxiety over treatment changes, and issues relating to distance, language, and mobility. Wherever possible, future studies should be designed to address these challenges.

Trial registration

ClinicalTrials.gov, NCT01540630.

EudraCT, 2010-023963-16. 07 Aug 2015.

AAPT Diagnostic Criteria for Peripheral Neuropathic Pain: Focal and Segmental Disorders

Peripheral neuropathic pain is among the most prevalent types of neuropathic pain. No comprehensive peripheral neuropathic pain classification system that incorporates contemporary clinical, diagnostic, biological, and psychological information exists. To address this need, this article covers the taxonomy for 4 focal or segmental peripheral neuropathic pain disorders, as part of the Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership and the American Pain Society (APS) collaborative to develop a standardized, evidence-based taxonomy initiative: the ACTTION-APS Pain Taxonomy (AAPT). The disorders-postherpetic neuralgia, persistent posttraumatic neuropathic pain, complex regional pain disorder, and trigeminal neuralgia-were selected because of their clinical and clinical research relevance. The multidimensional features of the taxonomy are suitable for clinical trials and can also facilitate hypothesis-driven case-control and cohort epidemiologic studies. PERSPECTIVE: The AAPT peripheral neuropathic pain taxonomy subdivides the peripheral neuropathic pain disorders into those that are generalized and symmetric and those that are focal or segmental and asymmetric. In this article, we cover the focal and segmental disorders: postherpetic neuralgia, persistent posttraumatic neuropathic pain, complex regional pain disorder, and trigeminal neuralgia. The taxonomy is evidence-based and multidimensional, with the following dimensions: 1) core diagnostic criteria; 2) common features; 3) common medical and psychiatric comorbidities; 4) neurobiological, psychosocial, and functional consequences; and 5) putative neurobiological and psychosocial mechanisms, risk factors, and protective factors.

Prevalence of Neuropathic Pain in Patients with Traumatic Brachial Plexus Injury: A Multicenter Prospective Hospital-Based Study

Objective

Prevalence and clinical characteristics of neuropathic pain due to traumatic brachial plexus injury.

Design

Observational epidemiological study.

Setting

Hospital-based multicenter study.

Subjects

One hundred seven prospectively enrolled patients with brachial plexus injury.

Methods

All the patients underwent clinical examination and neurophysiological testing for a definitive diagnosis of the brachial plexus lesion. The DN4 questionnaire was used to identify neuropathic pain, and the Neuropathic Pain Symptom Inventory (NPSI) to evaluate the different symptoms of neuropathic pain. The SF36 questionnaire and the Beck Depression Inventory (BDI) were used to assess quality of life and mood disturbances in patients with neuropathic pain.

Results

Of the 107 enrolled patients, 74 had pain (69%); neuropathic pain, as assessed by means of the DN4, was identified in 60 (56%) of these patients. According to the NPSI, the most frequent and severe pain type was the spontaneous burning pain. Clinical and neurophysiological findings showed that pain is unrelated to age but is associated with the severity of peripheral nerve damage. The SF36 questionnaire and BDI showed that neuropathic pain impairs quality of life and causes depression.

Conclusions

Our study provides information on the prevalence, characteristics, and variables associated with neuropathic pain due to traumatic brachial plexus injuries that might provide a basis for improving the clinical management of this condition.

A pain in the skin. Regenerating nerve sprouts are distinctly associated with ongoing burning pain in patients with diabetes

BACKGROUNDS

Patients with diabetic polyneuropathy commonly suffer from ongoing burning pain and dynamic mechanical allodynia. In this clinical and skin biopsy study, we aimed at assessing how intraepidermal regenerating nerve sprouts are associated with these two types of pain.

METHODS

We consecutively enrolled 85 patients with diabetic polyneuropathy. All patients underwent skin biopsy at the distal leg. Intraepidermal nerve fibres were immunostained with the anti-protein gene product 9.5 (PGP9.5) to quantify all intraepidermal nerve fibres, and the growth-associated protein 43 (GAP43) to quantify regenerating nerve sprouts.

RESULTS

We found that the GAP43-stained intraepidermal nerve fibre density and the ratio GAP43/PGP9.5 were significantly higher in patients with ongoing burning pain than in those without. The area of receiver operating characteristic (ROC) curve for the ratio GAP43/PGP9.5 was 0.74 and yielded a sensitivity and specificity for identifying ongoing burning pain of 72% and 71%, respectively. Conversely, although the density of PGP9.5 and GAP43 intraepidermal nerve fibre was higher in patients with dynamic mechanical allodynia than in those without, this difference was statistically weak and the ROC curve analysis of skin biopsy variables for this type of pain failed to reach the statistical significance.

CONCLUSION

Our clinical and skin biopsy study showed that ongoing burning pain was strongly associated with regenerating sprouts, as assessed with GAP43 immunostaining. This finding improves our understanding on the mechanisms underlying neuropathic pain in patients with diabetic polyneuropathy and suggests that the GAP43/PGP 9.5 ratio might be used as an objective marker for ongoing burning pain due to regenerating sprouts.

SIGNIFICANCE

Our skin biopsy study showing that regenerating sprouts, as assessed with GAP43-staining, were strongly associated with ongoing burning pain, improves our knowledge on the mechanisms underlying neuropathic pain in patients with diabetes.

Trigeminal Neuralgia

PURPOSE OF REVIEW

Although trigeminal neuralgia is well known to neurologists, recent developments in classification and clinical diagnosis, new MRI methods, and a debate about surgical options necessitate an update on the topic.

RECENT FINDINGS

Currently, a worldwide controversy exists regarding the classification, diagnostic process, and surgical treatment of trigeminal neuralgia. This controversy has been caused on one side by the recognition that some 50% of patients with trigeminal neuralgia, apart from characteristic paroxysmal attacks, also have continuous pain in the same territory, which results in greater diagnostic difficulties and is associated with a lower response to medical and surgical treatments. In contrast, recent developments in MRI methods allow differentiation between a mere neurovascular contact and an effective compression of the trigeminal root by an anomalous vessel, which implies more difficulties in the choice of surgical treatment, with the indication for microvascular decompression becoming more restricted.

SUMMARY

This article proposes that the diagnosis of trigeminal neuralgia, with or without concomitant continuous pain, must rely on clinical grounds only. Diagnostic tests are necessary to distinguish three etiologic categories: idiopathic trigeminal neuralgia (nothing is found), classic trigeminal neuralgia (an anomalous vessel produces morphologic changes of the trigeminal root near its entry into the pons), and secondary trigeminal neuralgia (due to major neurologic disease, such as multiple sclerosis or tumors at the cerebellopontine angle). Carbamazepine and oxcarbazepine (ie, voltage-gated, frequency-dependent sodium channel blockers) are still the first-choice medical treatment, although many patients experience significant side effects, and those with concomitant continuous pain respond less well to treatment. The development of sodium channel blockers that are selective for the sodium channel 1.7 (Nav1.7) receptor will hopefully help. Although all the surgical interventions (percutaneous ganglion lesions, gamma knife radiosurgery, and microvascular decompression) are very efficacious, precise MRI criteria for differentiating a real neurovascular compression from an irrelevant contact will be of benefit in better selecting patients for microvascular decompression.

A longitudinal study of painless and painful intercostobrachial neuropathy after breast cancer surgery

Intercostobrachial neuropathy, often resulting in neuropathic pain, is a common complication of breast cancer surgery. In this 1-year longitudinal study, we aimed at seeking information on the frequency, clinical features, and course of painless and painful intercostobrachial neuropathy. We enrolled 40 women previously undergoing breast cancer surgery. In these patients, we collected, at 3, 6 and 12 months after surgery, clinical and quantitative sensory testing (QST) variables to diagnose intercostobrachial neuropathy, DN4 questionnaire to identify neuropathic pain, Neuropathic Pain Symptom Inventory to assess the different neuropathic pain symptoms, the Beck Depression Inventory to assess depressive symptoms, and SF36 to assess quality of life and Patient Global Impression of Change. Clinical and QST examination showed an intercostobrachial neuropathy in 23 patients (57.5%). Out of the 23 patients, five experienced neuropathic pain, as assessed with clinical examination and DN4. Axillary surgery clearance was associated with an increased risk of intercostobrachial neuropathy. Whereas sensory disturbances improved during the 1-year observation, neuropathic pain did not. Nevertheless, Beck Depression Inventory, SF36, and the Patient Global Impression of Change scores significantly improved over time. Our study shows that although intercostobrachial neuropathy is a common complication of breast cancer surgery, neuropathic pain affects only a minor proportion of patients. After 1 year, sensory disturbances partially improve and have only a mild impact on mood and quality of life.

Scientific publications of European neurologists: a survey commissioned by the European Academy of Neurology

BACKGROUND AND PURPOSE

Bibliometric searches may provide an indirect assessment of research in a field or country. The European Academy of Neurology decided to investigate how article production was developing in European countries, as an indicator of neurological vitality.

METHODS

We searched two databases, Scopus and PubMed, for articles published by authors belonging to neurological institutions in all European countries, the USA, Brazil, China and Japan. The search assessed production in the period between 2000 and 2015. We calculated four indicators, i.e. gross neurological product (GNP) (which includes all articles published in any indexed journal), production in top neurological journals, GNP per inhabitant and GNP per gross domestic product.

RESULTS

All indicators greatly increased over time. The European GNP paralleled that of the USA and was higher than those of the other countries. Restricting the search to top neurological journals showed that, since 2012, European production grew faster than that of the USA. Germany had the highest production within Europe, Switzerland had the best ratio between GNP and inhabitants, and The Netherlands had the best ratio between GNP and gross domestic product.

CONCLUSIONS

Although this search had several limitations, the results were so straightforward that we can conclude that European neurology is highly active in the world. Future analyses should compare neurology with other main medical disciplines.

Identifying neuropathic pain in patients with multiple sclerosis: a cross-sectional multicenter study using highly specific criteria

BACKGROUND

Pain is a common and heterogeneous complication of multiple sclerosis (MS). In this multicenter, cross sectional study, we aimed at investigating the prevalence of pain in MS using highly specific criteria for distinguishing the different types of pain.

MATERIALS AND METHODS

After a structured interview, in patients with pain, clinical examination and DN4 questionnaire were used for distinguishing neuropathic and nociceptive pain. In subjects with neuropathic pain, the Neuropathic Pain Symptom Inventory was used for differentiating neuropathic pain symptoms.

RESULTS

We enrolled 1249 participants (832 F, 417 M, mean age 33.9 years, mean disease duration 8 years, mean EDSS 3.2); based on clinical evaluation and DN4 score 429 patients (34.34%) were classified with pain (470 pain syndromes): 286 nociceptive pain syndromes and 184 neuropathic pain syndromes. Multivariate analysis showed that pain was associated with age, gender and disease severity and that neuropathic pain was distinctly associated with EDSS.

CONCLUSIONS

Our study, providing definite information on the prevalence, characteristics and variables associated with neuropathic pain due to MS, shows that a more severe disease course is associated with a higher risk of neuropathic pain. Our findings might, therefore, provide a basis for improving the clinical management of this common MS complication.

Author Correction to: L-Acetyl-carnitine in Patients with Carpal Tunnel Syndrome: Effects on Nerve Protection, Hand Function and Pain

In the original publication the name of third author was incorrectly published.

Superiority of capsaicin 8% patch versus oral pregabalin on dynamic mechanical allodynia in patients with peripheral neuropathic pain

Background

Dynamic Mechanical Allodynia (DMA) is a typical symptom of neuropathic pain (NP). In a recent study, the capsaicin 8% patch was noninferior to pregabalin in overall peripheral NP relief. In this study, we report the comparison of the two treatments in relieving DMA.

Methods

In a randomized, open‐label, head‐to‐head, 8‐week study, 488 patients with peripheral NP were treated with the capsaicin 8% patch (one application) or an optimized dose of pregabalin. Assessments included the area and intensity of DMA, and the number of patients achieving complete resolution of DMA.

Results

At baseline, 253 patients in the capsaicin 8% patch group and 235 patients in the pregabalin group had DMA. From baseline to end of study, the change in DMA intensity was significantly in favour of the capsaicin 8% patch versus pregabalin [−0.63 (95% CI: −1.04, −0.23; p = 0.002)]. Similarly, the capsaicin 8% patch was superior to pregabalin in reducing the area of DMA [−39.5 cm² (95% CI: −69.1, −10.0; p = 0.009)] from baseline to end of study. Overall, a greater proportion of patients had a complete resolution of allodynia with capsaicin 8% patch treatment compared with pregabalin treatment (24.1% vs. 12.3%; p = 0.001) at end of study.

Conclusion

Capsaicin 8% treatment was superior to pregabalin in reducing the intensity and area of DMA, and in the number of patients with complete resolution of DMA.

Significance

The superiority of a topical treatment over pregabalin in relieving DMA supports the view that both peripheral and central sensitization can mediate allodynia.

A review of Neuropathic Pain: From Guidelines to Clinical Practice

Neuropathic pain is a chronic condition representing a significant burden for patients, society, and healthcare systems. The prevalence of neuropathic pain in the general population has been estimated at 7–8% and is expected to increase in the future. Neuropathic pain differs from nociceptive pain and requires a different therapeutic approach; and the management of neuropathic pain is complicated and challenging. This chapter discusses clinical practice guidelines for neuropathic pain and their usefulness in clinical practice.

Funding: Pfizer, Italy.

The third-stimulus temporal discrimination threshold: focusing on the temporal processing of sensory input within primary somatosensory cortex

The somatosensory temporal discrimination threshold (STDT) has been used in recent years to investigate time processing of sensory information, but little is known about the physiological correlates of somatosensory temporal discrimination. The objective of this study was to investigate whether the time interval required to discriminate between two stimuli varies according to the number of stimuli in the task. We used the third-stimulus temporal discrimination threshold (ThirdDT), defined as the shortest time interval at which an individual distinguishes a third stimulus following a pair of stimuli delivered at the STDT. The STDT and ThirdDT were assessed in 31 healthy subjects. In a subgroup of 10 subjects, we evaluated the effects of the stimuli intensity on the ThirdDT. In a subgroup of 16 subjects, we evaluated the effects of S1 continuous theta-burst stimulation (S1-cTBS) on the STDT and ThirdDT. Results show that ThirdDT is shorter than STDT. We found a positive correlation between STDT and ThirdDT values. As long as the stimulus intensity was within the perceivable and painless range, it did not affect ThirdDT values. S1-cTBS significantly affected both STDT and ThirdDT, although the latter was affected to a greater extent and for a longer period of time. We conclude that the interval needed to discriminate between time-separated tactile stimuli is related to the number of stimuli used in the task. STDT and ThirdDT are encoded in S1, probably by a shared tactile temporal encoding mechanism whose performance rapidly changes during the perception process. ThirdDT is a new method to measure somatosensory temporal discrimination.NEW & NOTEWORTHY To investigate whether the time interval required to discriminate between stimuli varies according to changes in the stimulation pattern, we used the third-stimulus temporal discrimination threshold (ThirdDT). We found that the somatosensory temporal discrimination acuity varies according to the number of stimuli in the task. The ThirdDT is a new method to measure somatosensory temporal discrimination and a possible index of inhibitory activity at the S1 level.

Triggering trigeminal neuralgia

Introduction Although it is widely accepted that facial pain paroxysms triggered by innocuous stimuli constitute a hallmark sign of trigeminal neuralgia, very few studies to date have systematically investigated the role of the triggers involved. In the recently published diagnostic classification, triggered pain is an essential criterion for the diagnosis of trigeminal neuralgia but no study to date has been designed to address this issue directly. In this study, we set out to determine, in patients with trigeminal neuralgia, how frequently triggers are present, which manoeuvres activate them and where cutaneous and mucosal trigger zones are located. Methods Clinical characteristics focusing on trigger factors were collected from 140 patients with trigeminal neuralgia, in a cross-sectional study design. Results Provocation of paroxysmal pain by various trigger manoeuvres was reported by 136 of the 140 patients. The most frequent manoeuvres were gentle touching of the face (79%) and talking (54%). Trigger zones were predominantly reported in the perioral and nasal region. Conclusion This study confirms that in trigeminal neuralgia, paroxysmal pain is associated with triggers in virtually all patients and supports the use of triggers as an essential diagnostic feature of trigeminal neuralgia.