Small fibre impairment predicts neuropathic pain in Guillain–Barré syndrome

Corneal Confocal Microscopy Identifies Corneal Nerve Loss in Patients With Guillain-Barré Syndrome

INTRODUCTION/AIMS

Patients with Guillain-Barré syndrome (GBS) commonly present with sensory loss and weakness, but they may also have neuropathic pain, elevated thermal thresholds, and intraepidermal nerve fiber loss. The primary aim of this study was to assess for evidence of small nerve fiber damage in patients with GBS.  METHODS: Nine patients with GBS and 15 age-matched healthy controls underwent CCM to quantify corneal nerve fiber density (CNFD), corneal nerve fiber length (CNFL), and corneal nerve branch density (CNBD), Douleur Neuropathique en 4 (DN4) to assess neuropathic pain, electrochemical skin conductance (ESC), vibration perception threshold (VPT), and nerve conduction studies.

RESULTS

CNFD (p = 0.008), CNFL (p = 0.011), CNBD (p = 0.005), and ESC on the hands (p = 0.024) and the feet (p = 0.046) were lower, whereas DN4 (p = 0.007) was higher in patients with GBS compared to healthy controls.

DISCUSSION

Patients with GBS have evidence of small nerve fiber damage as evidenced by corneal nerve fiber loss, neuropathic pain, and sudomotor dysfunction. CCM may add to the toolbox for the evaluation of small nerve fiber involvement in patients with GBS.

A clinical approach to the investigation and management of long COVID associated neuropathic pain

COVID-19 has been associated with a wide range of ongoing symptoms following recovery from the acute SARS-CoV-2 infection. Around one in three people with COVID-19 develop neurological symptoms with many reporting neuropathic pain and associated symptoms, including paraesthesia, numbness, and dysesthesia. Whilst the pathophysiology of long COVID-19-associated neuropathic pain remains unclear, it is likely to be multifactorial. Early identification, exclusion of common alternative causes, and a biopsychosocial approach to the management of the symptoms can help in relieving the burden of disease and improving the quality of life for patients.

Age-dependent small fiber neuropathy: Mechanistic insights from animal models

Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions.

Long-term outcomes of paediatric Guillain-Barré syndrome

AIM

To study long-term sequelae in children with Guillain-Barré syndrome (GBS).

METHOD

This was a prospective observational study with children from two French tertiary centres. Data were from clinical and several standardized scales or questionnaires.

RESULTS

Fifty-one patients were included with a median follow-up of 6 years 4 months (range 3-20 years) after the acute phase. The sequelae rate was 67% (95% confidence interval [CI] 53-78) and did not vary with time. Most children had minor sequelae (Guillain-Barré Syndrome Disability Score [GBSDS] = 1); only one was unable to run (GBSDS = 2). The most frequent complaints were paraesthesia (43%), pain (35%), and fatigue (31%). The neurological examination was abnormal in 18% of children, autonomy was compromised in 14%, and symptoms of depression occurred in 34%. The factors associated with late-onset sequelae were correlated with severity during the initial phase (i.e. initial GBSDS >4, odds ratio 6.6, 95% CI 1.8-33; p = 0.009). The predictive factors of more severe late-onset conditions were initial severity (p = 0.002) and sex (female patients; p = 0.01).

INTERPRETATION

Two-thirds of children with GBS had late-onset sequelae following an episode, often minor, but sometimes with continuing effects on their everyday lives. Particularly affected were those who had severe GBS during the acute phase and who lost the ability to walk.

WHAT THIS PAPER ADDS

Two-thirds of children with Guillain-Barré syndrome (GBS) had persistent sequelae. Sequelae were often minor, but daily repercussions of them were sometimes serious. Sequelae were significantly associated with severe GBS during the acute phase.

Macrophage accumulation in dorsal root ganglion is associated with neuropathic pain in experimental autoimmune neuritis

Background

Neuropathic pain is a common symptom of Guillain-Barré syndrome (GBS). The infiltration of macrophages in the dorsal root ganglion (DRG) contributed to neuropathic pain in nerve injury. The underlying mechanisms of neuropathic pain in patients with GBS remain unknown. Experimental autoimmune neuritis (EAN) is a useful mice model of GBS. Our study aimed to explore whether the infiltration of macrophages in DRG is associated with neuropathic pain of EAN.

Methods

Male C57BL/6 mice were randomly divided into two groups, the EAN group (n = 12) and the control group (n = 12). Six mice in each group were sacrificed after anesthetization in the attack and remission phase, respectively. The 50% paw withdrawal threshold and clinical score were measured, and macrophages with its subtypes were detected in the spleen and DRG tissue.

Results

More macrophages infiltrated the DRG of the EAN group in the attack phase and mostly surrounded neurons in the DRG. The proportion of macrophages and pro-inflammatory macrophages in the spleen of mice with EAN was significantly higher than the control group in the attack phase.

Conclusion

The infiltration of macrophages in DRG might be associated with neuropathic pain of EAN and pro-inflammatory macrophages may involve in neuropathic pain of EAN.

Advances and challenges in neuropathic pain: a narrative review and future directions

Over the past few decades, substantial advances have been made in neuropathic pain clinical research. An updated definition and classification have been agreed. Validated questionnaires have improved the detection and assessment of acute and chronic neuropathic pain; and newer neuropathic pain syndromes associated with COVID-19 have been described. The management of neuropathic pain has moved from empirical to evidence-based medicine. However, appropriately targeting current medications and the successful clinical development of drugs acting on new targets remain challenging. Innovative approaches to improving therapeutic strategies are required. These mainly encompass rational combination therapy, drug repurposing, non-pharmacological approaches (such as neurostimulation techniques), and personalised therapeutic management. This narrative review reports historical and current perspectives regarding the definitions, classification, assessment, and management of neuropathic pain and explores potential avenues for future research.

Mirror peripheral neuropathy and unilateral chronic neuropathic pain: insights from asymmetric neurological patterns in leprosy

ABSTRACT

Leprosy-related multiple mononeuropathy offers a pattern of impairment where neuropathy with and without neuropathic pain (NeP) are present in the same individual, thus allowing to investigate peripheral sensory and innervation in both conditions. This cross-sectional study collected data on clinical and neurological examination, pain assessment questionnaires, quantitative sensory test, and intraepidermal nerve fiber density of patients with leprosy and divided the cohort into 2 groups: with NeP (P+) and without NeP (P-). Furthermore, we assessed mirror body areas in the same NeP individuals with bilateral neuropathy also presenting unilateral NeP. Pain-free patients having unilateral neuropathy were controls. A total of 37 P+ and 22 P- patients were evaluated. Limb areas with NeP had signs of C-fiber dysfunction and hyperesthesia on quantitative sensory testing compared with limb areas having neuropathy without NeP. Skin denervation was found in all patients with leprosy. Comparisons of limbs with and without neuropathy and with and without NeP revealed that higher heat pain thresholds (HPTs) were associated with neuropathic pain areas, whereas less altered HPT was correlated with higher fiber density. Furthermore, a relationship was found between time of leprosy treatment termination and more intense neuropathy, expressed by HPT increasing 0.03°C each month. As expected, interindividual comparisons failed to show differences in intraepidermal nerve fiber density and subepidermal plexus areas between P+ and P- patients ( P = 0.2980, P = 0.9044; respectively). Higher HPT and lower mechanical detection threshold were related to NeP. This study pointed out the relevance of intraindividual comparisons including mirror areas when assessing local changes in peripheral NeP.

Intractable Neuropathic Pain in COVID-19-Induced Guillain-Barré Syndrome: A Case Report

There is limited literature specific to neuropathic pain in coronavirus disease 2019 (COVID-19)-induced acute inflammatory demyelinating polyneuropathy (AIDP). We present a unique case of a 20-year-old vaccinated female with a past medical history of chronic hepatitis B virus and untreated anxiety who presented to the emergency department due to an intractable headache and horizontal diplopia in the setting of active COVID-19 infection. During acute hospitalization, the patient was diagnosed with the Miller-Fisher variant of Guillain-Barré syndrome (GBS), a disease with a known association with COVID-19. While in the ICU, the patient developed severe, 10/10-rated, distal, symmetric burning pain with associated allodynia requiring a multimodal regimen with combinations of intravenous narcotics, neuropathic medications, topical agents, and desensitization training to attempt to control her pain. Rehabilitation psychology was consulted while she was in chronic ventilatory rehabilitation for supplementation of behavioral pain management strategies with pharmacological approaches for continued pain. After several months and completion of a comprehensive inpatient rehabilitation program, the patient was weaned off intravenous narcotics and prescribed oral pain medications. This patient had the optimal response to amitriptyline, which likely aided in the co-treatment of psychological manifestations of COVID-19 and prolonged hospitalization. This study highlights the pathogenicity of COVID-19-induced AIDP, its potential severity, and the importance of a multidisciplinary approach to managing it.

Neuropathic Pain Symptom Inventory (NPSI) Questionnaire-Persian Version Can Differentiate Neuropathic from Non-Neuropathic Pain

BACKGROUND

Neuropathic pain (NP) is a common condition that impacts life negatively. This type of pain responds poorly to treatment. Neuropathic Pain Symptom Inventory (NPSI) is a common instrument used for the assessment of NP response to the treatment.

AIM

The current study aims to validate the Persian version of NPSI (PV-NPSI).

METHODS

The current study has been conducted on 162 patients experiencing pain from neuropathic ornon-neuropathic origin. The Persian version of NPSI was proposed through standard protocol and responded to by patients twice: at baseline within an interval of 3 hours and then again within 1 month. Its correlation with the patient global impression of change (PGIC) and the clinical global impression of change (CGIC) was assessed. In addition, the validity and reliability of the PV-NPSI was evaluated.

RESULTS

The reliability Cronbach's alpha of PV-NPSI was 0.834 and test-retest intraclass-coefficient was calculated as 0.983 (95% confidence interval [CI]: 0.977-0.988; p < .001). In addition, the measured coefficient sensitivity to change based on PGIC and CGIC was 0.859 for both. Receiver operating characteristic (ROC) curve for the diagnosis of NP revealed area under curve (AUC) of 0.936 (p < .001; 95%CI: 0.894-0.978).

CONCLUSIONS

Based on the current study's findings, the PV-NPSI is a reliable and valid means for the differentiation of NP from the other types of pain in patients with several musculoskeletal pain complaints, but we cannot determine a cutoff point for it. Also, this questionnaire can be efficiently used for the assessment of response to NP treatment.

Pathophysiology of Nociception and Rare Genetic Disorders with Increased Pain Threshold or Pain Insensitivity

Pain and nociception are different phenomena. Nociception is the result of complex activity in sensory pathways. On the other hand, pain is the effect of interactions between nociceptive processes, and cognition, emotions, as well as the social context of the individual. Alterations in the nociceptive route can have different genesis and affect the entire sensorial process. Genetic problems in nociception, clinically characterized by reduced or absent pain sensitivity, compose an important chapter within pain medicine. This chapter encompasses a wide range of very rare diseases. Several genes have been identified. These genes encode the Nav channels 1.7 and 1.9 (SCN9A, and SCN11A genes, respectively), NGFβ and its receptor tyrosine receptor kinase A, as well as the transcription factor PRDM12, and autophagy controllers (TECPR2). Monogenic disorders provoke hereditary sensory and autonomic neuropathies. Their clinical pictures are extremely variable, and a precise classification has yet to be established. Additionally, pain insensitivity is described in diverse numerical and structural chromosomal abnormalities, such as Angelman syndrome, Prader Willy syndrome, Chromosome 15q duplication syndrome, and Chromosome 4 interstitial deletion. Studying these conditions could be a practical strategy to better understand the mechanisms of nociception and investigate potential therapeutic targets against pain.

The structure of sensory afferent compartments in health and disease

Primary sensory neurons are a heterogeneous population of cells able to respond to both innocuous and noxious stimuli. Like most neurons they are highly compartmentalised, allowing them to detect, convey and transfer sensory information. These compartments include specialised sensory endings in the skin, the nodes of Ranvier in myelinated axons, the cell soma and their central terminals in the spinal cord. In this review, we will highlight the importance of these compartments to primary afferent function, describe how these structures are compromised following nerve damage and how this relates to neuropathic pain.

Neuropathic Pain in Guillain-Barre Syndrome: Association with Rehabilitation Outcomes and Quality of Life

BACKGROUND

Neuropathic pain contributes significantly to the morbidity and affects the quality of life adversely in Guillain-Barre syndrome (GBS).

OBJECTIVE

To study neuropathic pain profile in GBS and association with rehabilitation outcomes and effect on the quality of life.

METHODS

Observational study conducted in rehabilitation setting of a tertiary care hospital among adult GBS patients of less than 3 months duration. Assessment was done at the time of admission and discharge with Pain-detect questionnaire (PD-Q), Neuropathic pain scale (NPS), SF 36 survey, Medical Research Council (MRC) score, INCAT sensory sum score (ISS), Overall Disability sum-score (ODSS), Hughes disability score (HDS), Hospital Anxiety and Depression scale (HADS), and Fatigue Severity scale (FSS). Neuropathic pain was managed as per routine protocol and rehabilitation program was individualized.

RESULTS

32 participants (26 males) with median age of 34.50 years were included. Eighteen (56.25%) patients had neuropathic pain on PD-Q at admission. The median intensity of pain on NPS scale was 47 at admission which decreased significantly to 14 at discharge. Pain group showed significant association with sensory impairment, CSF protein, and emotional domains of QOL while no association with disability.

CONCLUSION

Neuropathic pain is associated with sensory impairment in GBS and markedly affects the quality of life, especially emotional, family, and social activities.

Studying human nociceptors: from fundamentals to clinic

Chronic pain affects one in five of the general population and is the third most important cause of disability-adjusted life-years globally. Unfortunately, treatment remains inadequate due to poor efficacy and tolerability. There has been a failure in translating promising preclinical drug targets into clinic use. This reflects challenges across the whole drug development pathway, from preclinical models to trial design. Nociceptors remain an attractive therapeutic target: their sensitization makes an important contribution to many chronic pain states, they are located outside the blood-brain barrier, and they are relatively specific. The past decade has seen significant advances in the techniques available to study human nociceptors, including: the use of corneal confocal microscopy and biopsy samples to observe nociceptor morphology, the culture of human nociceptors (either from surgical or post-mortem tissue or using human induced pluripotent stem cell derived nociceptors), the application of high throughput technologies such as transcriptomics, the in vitro and in vivo electrophysiological characterization through microneurography, and the correlation with pain percepts provided by quantitative sensory testing. Genome editing in human induced pluripotent stem cell-derived nociceptors enables the interrogation of the causal role of genes in the regulation of nociceptor function. Both human and rodent nociceptors are more heterogeneous at a molecular level than previously appreciated, and while we find that there are broad similarities between human and rodent nociceptors there are also important differences involving ion channel function, expression, and cellular excitability. These technological advances have emphasized the maladaptive plastic changes occurring in human nociceptors following injury that contribute to chronic pain. Studying human nociceptors has revealed new therapeutic targets for the suppression of chronic pain and enhanced repair. Cellular models of human nociceptors have enabled the screening of small molecule and gene therapy approaches on nociceptor function, and in some cases have enabled correlation with clinical outcomes. Undoubtedly, challenges remain. Many of these techniques are difficult to implement at scale, current induced pluripotent stem cell differentiation protocols do not generate the full diversity of nociceptor populations, and we still have a relatively poor understanding of inter-individual variation in nociceptors due to factors such as age, sex, or ethnicity. We hope our ability to directly investigate human nociceptors will not only aid our understanding of the fundamental neurobiology underlying acute and chronic pain but also help bridge the translational gap.

Potential for increased prevalence of neuropathic pain after the COVID-19 pandemic

Although coronavirus disease 2019 (COVID-19) most commonly manifests with acute respiratory symptoms, one very common symptom of COVID-19 is pain. As COVID-19 often causes peripheral or central neurological complications, it is anticipated that a number of the chronic pain complications of COVID-19 will be neuropathic. This review first examines the most common viral infections responsible for neurological complications including neuropathic pain. These encompass herpes zoster, HIV, poliovirus, enteroviruses, and several tropical viruses. Neurological complications of COVID-19 including in particular Guillain-Barré syndrome, myelitis, and stroke are reviewed with regards to their potential risk of chronic neuropathic pain. Prospective longitudinal cohorts of patients should be implemented to evaluate the exact risk of neuropathic pain after COVID-19.

Longitudinal study of neuropathic pain in patients with Guillain-Barré syndrome

OBJECTIVE

The aim of this study was to analyze neuropathic pain (NeP) and its therapy in patients with Guillain-Barré syndrome (GBS) during a 6-month follow-up period.

METHOD

This longitudinal multicenter study included 69 newly diagnosed adult GBS patients. NeP diagnosis was based on the criteria of Finnerup and confirmed by the PainDETECT Questionnaire (PD-Q). Severity of GBS was assessed by GBS disability scale (GDS). Patients were assessed: on day 14 (D14), day 28 (D28), month 3 (M3), and month 6 (M6) from the disease onset.

RESULTS

At D14, pain was present in 85.5% of patients, while 26.4% had NeP. At M6, 72.5% of patients had pain, 20.0% of them NeP. In acute GBS, pain intensity was higher in patients with NeP compared to those with non-NeP (p < 0.01). Pain intensity in patients with NeP did not change during time, but it decreased in patients with non-NeP at M6 (p < 0.05). Around 20% of GBS patients were on specific NeP medication throughout the observed period. One quarter of patients with NeP were not on specific NeP drug in the acute phase. Up to one third of patients with NeP were on NeP medication but still had significant NeP. Pooled PD-Q score was in correlation with pooled GDS score (rho = + 0.43, p < 0.01).

CONCLUSIONS

NeP is a common and potentially severe symptom in GBS that may persist for months. It is important to recognize NeP, start specific treatment on time, in adequate doses, and for prolonged period of time.

Altered pain processing in patients with type 1 and 2 diabetes: systematic review and meta-analysis of pain detection thresholds and pain modulation mechanisms

The first signs of diabetic neuropathy typically result from small-diameter nerve fiber dysfunction. This review synthesized the evidence for small-diameter nerve fiber neuropathy measured via quantitative sensory testing (QST) in patients with diabetes with and without painful and non-painful neuropathies. Electronic databases were searched to identify studies in patients with diabetes with at least one QST measure reflecting small-diameter nerve fiber function (thermal or electrical pain detection threshold, contact heat-evoked potentials, temporal summation or conditioned pain modulation). Four groups were compared: patients with diabetes (1) without neuropathy, (2) with non-painful diabetic neuropathy, (3) with painful diabetic neuropathy and (4) healthy individuals. Recommended methods were used for article identification, selection, risk of bias assessment, data extraction and analysis. For the meta-analyses, data were pooled using random-effect models. Twenty-seven studies with 2422 participants met selection criteria; 18 studies were included in the meta-analysis. Patients with diabetes without symptoms of neuropathy already showed loss of nerve function for heat (standardized mean difference (SMD): 0.52, p<0.001), cold (SMD: -0.71, p=0.01) and electrical pain thresholds (SMD: 1.26, p=0.01). Patients with non-painful neuropathy had greater loss of function in heat pain threshold (SMD: 0.75, p=0.01) and electrical stimuli (SMD: 0.55, p=0.03) compared with patients with diabetes without neuropathy. Patients with painful diabetic neuropathy exhibited a greater loss of function in heat pain threshold (SMD: 0.55, p=0.005) compared with patients with non-painful diabetic neuropathy. Small-diameter nerve fiber function deteriorates progressively in patients with diabetes. Because the dysfunction is already present before symptoms occur, early detection is possible, which may assist in prevention and effective management of diabetic neuropathy.

Small fiber neuropathy in unexpected clinical settings: a review

Small fiber neuropathy (SFN) is being recognized with increasing frequency in neuromuscular practice due to improved diagnostic techniques. Although there are some common etiologies, up to one-third of cases are considered idiopathic. In recent years, several disorders have unexpectedly been reported in association with SFN, on clinical grounds and complementary investigations, including quantitative sensory testing, intraepidermal nerve fiber density and confocal corneal microscopy. Knowledge of these disorders is important in clinical practice as increased awareness enables prompt diagnosis of SFN in these settings and early optimal therapeutic management of affected patients. Furthermore, these new developments may lead to a better understanding of the pathophysiologic mechanisms underlying SFN in these different disorders as well as, in some cases, an expanded spectrum of affected organs and systems. This article reviews these reported associations, their possible pathophysiologic bases, and the potential resulting management implications.

Pain during the acute phase of Guillain-Barré syndrome

In this study, we tried to describe the characteristics of pain and explore the association between the incidence of pain and abnormal laboratory test results in patients during the acute phase of Guillain-Barré syndrome (GBS).This retrospective cohort study enrolled 252 patients with GBS who were in the acute phase of the disease. We collected data regarding the location and type of pain, the onset time, clinical variables and laboratory tests, including the levels of uric acid (UA), albumin, cerebrospinal fluid protein (CSFP), cerebrospinal fluid glucose (CSFG), fasting glucose upon admission, and blood creatinine. The pain descriptors were compared to the severity of disease and laboratory examination results.Around 34.5% of the patients reported pain during the acute phase of GBS. Pain was negatively correlated with the disease severity during the acute phase. In total, 29 of the 87 (33.3%) patients reported pain during the 2 weeks preceding the onset of weakness. The concentration of CSFP was positively associated with the incidence of pain, while the concentrations of UA and albumin were not correlated with the incidence of pain.We found that 33.3% of the GBS patients experienced pain within 2 weeks of onset, and the pain was positively associated with CSFP concentration but was not correlated with disease severity.

Mitochondrial damage and "plugging" of transport selectively in myelinated, small-diameter axons are major early events in peripheral neuroinflammation

Background

Small-diameter, myelinated axons are selectively susceptible to dysfunction in several inflammatory PNS and CNS diseases, resulting in pain and degeneration, but the mechanism is not known.

Methods

We used in vivo confocal microscopy to compare the effects of inflammation in experimental autoimmune neuritis (EAN), a model of Guillain-Barré syndrome (GBS), on mitochondrial function and transport in large- and small-diameter axons. We have compared mitochondrial function and transport in vivo in (i) healthy axons, (ii) axons affected by experimental autoimmune neuritis, and (iii) axons in which mitochondria were focally damaged by laser induced photo-toxicity.

Results

Mitochondria affected by inflammation or laser damage became depolarized, fragmented, and immobile. Importantly, the loss of functional mitochondria was accompanied by an increase in the number of mitochondria transported towards, and into, the damaged area, perhaps compensating for loss of ATP and allowing buffering of the likely excessive Ca²⁺ concentration. In large-diameter axons, healthy mitochondria were found to move into the damaged area bypassing the dysfunctional mitochondria, re-populating the damaged segment of the axon. However, in small-diameter axons, the depolarized mitochondria appeared to “plug” the axon, obstructing, sometimes completely, the incoming (mainly anterograde) transport of mitochondria. Over time (~ 2 h), the transported, functional mitochondria accumulated at the obstruction, and the distal part of the small-diameter axons became depleted of functional mitochondria.

Conclusions

The data show that neuroinflammation, in common with photo-toxic damage, induces depolarization and fragmentation of axonal mitochondria, which remain immobile at the site of damage. The damaged, immobile mitochondria can “plug” myelinated, small-diameter axons so that successful mitochondrial transport is prevented, depleting the distal axon of functioning mitochondria. Our observations may explain the selective vulnerability of small-diameter axons to dysfunction and degeneration in a number of neurodegenerative and neuroinflammatory disorders.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1094-8) contains supplementary material, which is available to authorized users.

Peripheral neuropathic pain: a mechanism-related organizing principle based on sensory profiles

More than 1100 patients with neuropathic pain were examined using quantitative sensory testing. Independent of the etiology, 3 subtypes with distinct sensory profiles were identified and replicated.

Patients with neuropathic pain are heterogeneous in etiology, pathophysiology, and clinical appearance. They exhibit a variety of pain-related sensory symptoms and signs (sensory profile). Different sensory profiles might indicate different classes of neurobiological mechanisms, and hence subgroups with different sensory profiles might respond differently to treatment. The aim of the investigation was to identify subgroups in a large sample of patients with neuropathic pain using hypothesis-free statistical methods on the database of 3 large multinational research networks (German Research Network on Neuropathic Pain (DFNS), IMI-Europain, and Neuropain). Standardized quantitative sensory testing was used in 902 (test cohort) and 233 (validation cohort) patients with peripheral neuropathic pain of different etiologies. For subgrouping, we performed a cluster analysis using 13 quantitative sensory testing parameters. Three distinct subgroups with characteristic sensory profiles were identified and replicated. Cluster 1 (sensory loss, 42%) showed a loss of small and large fiber function in combination with paradoxical heat sensations. Cluster 2 (thermal hyperalgesia, 33%) was characterized by preserved sensory functions in combination with heat and cold hyperalgesia and mild dynamic mechanical allodynia. Cluster 3 (mechanical hyperalgesia, 24%) was characterized by a loss of small fiber function in combination with pinprick hyperalgesia and dynamic mechanical allodynia. All clusters occurred across etiologies but frequencies differed. We present a new approach of subgrouping patients with peripheral neuropathic pain of different etiologies according to intrinsic sensory profiles. These 3 profiles may be related to pathophysiological mechanisms and may be useful in clinical trial design to enrich the study population for treatment responders.

Neuropathic pain in experimental autoimmune neuritis is associated with altered electrophysiological properties of nociceptive DRG neurons

Guillain-Barré syndrome (GBS) is an acute, immune-mediated polyradiculoneuropathy characterized by rapidly progressive paresis and sensory disturbances. Moderate to severe and often intractable neuropathic pain is a common symptom of GBS, but its underlying mechanisms are unknown. Pathology of GBS is classically attributed to demyelination of large, myelinated peripheral fibers. However, there is increasing evidence that neuropathic pain in GBS is associated with impaired function of small, unmyelinated, nociceptive fibers. We therefore examined the functional properties of small DRG neurons, the somata of nociceptive fibers, in a rat model of GBS (experimental autoimmune neuritis=EAN). EAN rats developed behavioral signs of neuropathic pain. This was accompanied by a significant shortening of action potentials due to a more rapid repolarization and an increase in repetitive firing in a subgroup of capsaicin-responsive DRG neurons. Na⁺ current measurements revealed a significant increase of the fast TTX-sensitive current and a reduction of the persistent TTX-sensitive current component. These changes of Na⁺ currents may account for the significant decrease in AP duration leading to an overall increase in excitability and are therefore possibly directly linked to pathological pain behavior. Thus, like in other animal models of neuropathic and inflammatory pain, Na⁺ channels seem to be crucially involved in the pathology of GBS and may constitute promising targets for pain modulating pharmaceuticals.

Amplitudes of Pain-Related Evoked Potentials Are Useful to Detect Small Fiber Involvement in Painful Mixed Fiber Neuropathies in Addition to Quantitative Sensory Testing - An Electrophysiological Study

To investigate the usefulness of pain-related evoked potentials (PREP) elicited by electrical stimulation for the identification of small fiber involvement in patients with mixed fiber neuropathy (MFN). Eleven MFN patients with clinical signs of large fiber impairment and neuropathic pain and ten healthy controls underwent clinical and electrophysiological evaluation. Small fiber function, electrical conductivity and morphology were examined by quantitative sensory testing (QST), PREP, and skin punch biopsy. MFN was diagnosed following clinical and electrophysiological examination (chronic inflammatory demyelinating neuropathy: n = 6; vasculitic neuropathy: n = 3; chronic axonal ­neuropathy: n = 2). The majority of patients with MFN characterized their pain by descriptors that mainly represent C-fiber-mediated pain. In QST, patients displayed elevated cold, warm, mechanical, and vibration detection thresholds and cold pain thresholds indicative of MFN. PREP amplitudes in patients correlated with cold (p < 0.05) and warm detection thresholds (p < 0.05). Burning pain and the presence of par-/dysesthesias correlated negatively with PREP amplitudes (p < 0.05). PREP amplitudes correlating with cold and warm detection thresholds, burning pain, and par-/dysesthesias support employing PREP amplitudes as an additional tool in conjunction with QST for detecting small fiber impairment in patients with MFN.

Small-nerve-fiber pathology in critical illness documented by serial skin biopsies

INTRODUCTION

Small-fiber pathology can develop in the acute phase of critical illness and may explain chronic sensory impairment and pain in critical care survivors.

METHODS

Eleven adult ischemic stroke patients in a neurocritical care unit were enrolled in an observational cohort study. Intraepidermal nerve fiber density (IENFD) in the distal leg was assessed on admission to the intensive care unit and 10-14 days later, together with electrophysiological testing.

RESULTS

Of the 11 patients recruited, 9 (82%) had sepsis or multiple-organ failure. Median IENFD on admission (5.05 fibers/mm) decreased significantly to 2.18 fibers/mm (P < 0.001), and abnormal IENFD was found in 6 patients (54.5%). Electrodiagnostic signs of large-fiber neuropathy and/or myopathy were found in 6 patients (54.5%), and autonomic dysfunction was found in 2 patients (18.2%).

CONCLUSION

Serial IENFD measurements confirmed the development of small-fiber sensory involvement in the acute phase of critical illness.

The relationship of nerve fibre pathology to sensory function in entrapment neuropathy

The impact of peripheral entrapment neuropathies on target innervation remains unknown. Using quantitative sensory testing, neurophysiology and skin biopsies, Schmid et al. demonstrate that carpal tunnel syndrome affects large fibres and their nodal complexes, but is also associated with a reduction in the number and functioning of small sensory axons.

Surprisingly little is known about the impact of entrapment neuropathy on target innervation and the relationship of nerve fibre pathology to sensory symptoms and signs. Carpal tunnel syndrome is the most common entrapment neuropathy; the aim of this study was to investigate its effect on the morphology of small unmyelinated as well as myelinated sensory axons and relate such changes to somatosensory function and clinical symptoms. Thirty patients with a clinical and electrophysiological diagnosis of carpal tunnel syndrome [17 females, mean age (standard deviation) 56.4 (15.3)] and 26 age and gender matched healthy volunteers [18 females, mean age (standard deviation) 51.0 (17.3)] participated in the study. Small and large fibre function was examined with quantitative sensory testing in the median nerve territory of the hand. Vibration and mechanical detection thresholds were significantly elevated in patients with carpal tunnel syndrome (P < 0.007) confirming large fibre dysfunction and patients also presented with increased thermal detection thresholds (P < 0.0001) indicative of C and Aδ-fibre dysfunction. Mechanical and thermal pain thresholds were comparable between groups (P > 0.13). A skin biopsy was taken from a median nerve innervated area of the proximal phalanx of the index finger. Immunohistochemical staining for protein gene product 9.5 and myelin basic protein was used to evaluate morphological features of unmyelinated and myelinated axons. Evaluation of intraepidermal nerve fibre density showed a striking loss in patients (P < 0.0001) confirming a significant compromise of small fibres. The extent of Meissner corpuscles and dermal nerve bundles were comparable between groups (P > 0.07). However, patients displayed a significant increase in the percentage of elongated nodes (P < 0.0001), with altered architecture of voltage-gated sodium channel distribution. Whereas neither neurophysiology nor quantitative sensory testing correlated with patients’ symptoms or function deficits, the presence of elongated nodes was inversely correlated with a number of functional and symptom related scores (P < 0.023). Our findings suggest that carpal tunnel syndrome does not exclusively affect large fibres but is associated with loss of function in modalities mediated by both unmyelinated and myelinated sensory axons. We also document for the first time that entrapment neuropathies lead to a clear reduction in intraepidermal nerve fibre density, which was independent of electrodiagnostic test severity. The presence of elongated nodes in the target tissue further suggests that entrapment neuropathies affect nodal structure/myelin well beyond the focal compression site. Interestingly, nodal lengthening may be an adaptive phenomenon as it inversely correlates with symptom severity.

Small nerve fiber pathology in critical illness

BACKGROUND

Degeneration of intraepidermal nerve fibers (IENF) is a hallmark of small fiber neuropathy of different etiology, whose clinical picture is dominated by neuropathic pain. It is unknown if critical illness can affect IENF.

METHODS

We enrolled 14 adult neurocritical care patients with prolonged intensive care unit (ICU) stay and artificial ventilation (≥ 3 days), and no previous history or risk factors for neuromuscular disease. All patients underwent neurological examination including evaluation of consciousness, sensory functions, muscle strength, nerve conduction study and needle electromyography, autonomic dysfunction using the finger wrinkling test, and skin biopsy for quantification of IENF and sweat gland innervation density during ICU stay and at follow-up visit. Development of infection, sepsis and multiple organ failure was recorded throughout the ICU stay.

RESULTS

Of the 14 patients recruited, 13 (93%) had infections, sepsis or multiple organ failure. All had severe and non-length dependent loss of IENF. Sweat gland innervation was reduced in all except one patient. Of the 7 patients available for follow-up visit, three complained of diffuse sensory loss and burning pain, and another three showed clinical dysautonomia.

CONCLUSIONS

Small fiber pathology can develop in the acute phase of critical illness and may explain chronic sensory impairment and pain in neurocritical care survivors. Its impact on long term disability warrants further studies involving also non-neurologic critical care patients.

Neuropathic pain in animal models of nervous system autoimmune diseases

Neuropathic pain is a frequent chronic presentation in autoimmune diseases of the nervous system, such as multiple sclerosis (MS) and Guillain-Barre syndrome (GBS), causing significant individual disablement and suffering. Animal models of experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune neuritis (EAN) mimic many aspects of MS and GBS, respectively, and are well suited to study the pathophysiology of these autoimmune diseases. However, while much attention has been devoted to curative options, research into neuropathic pain mechanisms and relief has been somewhat lacking. Recent studies have demonstrated a variety of sensory abnormalities in different EAE and EAN models, which enable investigations of behavioural changes, underlying mechanisms, and potential pharmacotherapies for neuropathic pain associated with these diseases. This review examines the symptoms, mechanisms, and clinical therapeutic options in these conditions and highlights the value of EAE and EAN animal models for the study of neuropathic pain in MS and GBS.

Management of painful neuropathies

Neuropathic pain is the most common type of pain in neuropathy. In painful polyneuropathies the pain usually has a "glove and stocking" distribution. The pain may be predominantly spontaneous, e.g., with a burning, pricking, or shooting character or characterized by evoked pain such as mechanical or cold allodynia. In the clinical setting, the prevention of painful neuropathies and treatment of underlying neuropathy remains inadequate and thus symptomatic treatment of the pain and related disability needs to be offered. Most randomized, double-blind, placebo-controlled trials (RCTs) published in painful neuropathy have been conducted in patients with diabetes and to what extent a treatment which is found effective in painful diabetic polyneuropathy can be expected to relieve other conditions like chemotherapy- or HIV-induced neuropathy is unknown. Tricyclic antidepressants (TCAs), gabapentin, pregabalin, and serotonin noradrenaline reuptake inhibitors (SNRIs) are first drug choices. In patients with localized neuropathic pain, a topical lidocaine patch may also be considered. Second-line treatments are tramadol and other opioids. New types of treatment include botulinum toxin type A (BTX-A), high-dose capsaicin patches, and cannabinoids. Other types of anticonvulsant drugs such as lamotrigine, oxcarbazepine, and lacosamide have a more questionable efficacy in painful polyneuropathy but may have an effect in a subgroup of patients. Combination therapy may be considered in patients with insufficient effect from one drug. Treatment is usually a trial-and-error process and has to be individualized to the single patient, taking into account all comorbidities such as possible concomitant depression, anxiety, diseases, and drug interactions. Side-effects to antidepressants include dry mouth, nausea, constipation, orthostatic hypotension, and sedation. ECG should always be obtained prior to treatment with TCAs, which also should not be used in patients with cardiac incompensation and epilepsy. The most common side-effects of gabapentin and pregabalin are CNS-related side-effects with dizziness and somnolence. Peripheral edema, weight gain, nausea, vertigo, asthenia, dry mouth, and ataxia may also occur. Topical treatments are better tolerated due to lack of systemic side-effects but there is still limited evidence for the long-term efficacy of these drugs. With available drugs, the average pain reduction is about 20-30%, and only 20-35% of the patients will achieve at least 50% pain reduction, which stresses the need of a multidisciplinary approach to pain treatment.

The Guillain-Barré syndrome

The latest estimation for the frequency of Guillain-Barré syndrome (GBS) is 1.1 to 1.8 per 100000 persons per year. Guillain-Barré syndrome is today divided into two major subtypes: acute inflammatory demyelinating polyneuropathy (AIDP) and the axonal subtypes, acute motor axonal neuropathy (AMAN) and acute motor and sensory axonal neuropathy (AMSAN). The axonal forms of GBS are caused by certain autoimmune mechanisms, due to a molecular mimicry between antecedent bacterial infection (particularly Campylobacter jejuni) and human peripheral nerve gangliosides. Improvements in patient management in intensive care units has permitted a dramatic drop in mortality rates. Immunotherapy, including plasma exchange (PE) or intravenous immunoglobulin (IVIg), seems to shorten the time to recovery, but their effect remains limited. Further clinical investigations are needed to assess the effect of PE or IVIg on the GBS patients with mild affection, no response, or relapse.

Unmyelinated and myelinated skin nerve damage in Guillain-Barré syndrome: correlation with pain and recovery

We performed a prospective study in 32 patients with Guillain-Barré syndrome (GBS) or its variants to correlate intraepidermal nerve fiber density (IENFD) at the distal leg and lumbar region with pain, autonomic dysfunction, and outcome. In the acute phase, IENFD was reduced in 60% and 61.9% of patients at the distal leg and lumbar region, respectively. In the acute phase, 43.7% of patients complained of neuropathic pain. Their IENFD at the distal leg was significantly lower than in patients without pain (P<.001) and correlated with pain intensity (r(s)=-0.51; P=.003). Intriguingly, also patients with the pure motor variant of GBS and pain had low IENFD. At 6-month follow-up, only 3 patients complained of persisting neuropathic pain, whereas 3 patients reported late-onset pain symptoms. IENFD in the acute phase did not predict presence or intensity of pain at 6-month follow-up. IENFD in the acute phase did not correlate with clinical dysautonomia or GBS severity at nadir. However, it correlated with poorer GBS disability score at 6 months (P=.04), GBS score at nadir (P=.03), and clinically probable dysautonomia (P=.004). At 6-month follow-up, median IENFD remained significantly low both at the distal leg (P=.024) and lumbar region (P=.005). Double and triple staining confocal microscope studies showed diffuse damage of myelinated dermal nerves along with axonal degeneration, and mononuclear cell infiltration. Unmyelinated and myelinated skin nerves are diffusely affected in GBS and its variants, including the pure motor form. IENFD declines early, remains low over time, correlates with pain severity in the acute phase, and may predict long-term disability.

Psychometric validation of the Portuguese version of the Neuropathic Pain Symptoms Inventory

BACKGROUND

It has been shown that different symptoms or symptom combinations of neuropathic pain (NeP) may correspond to different mechanistic backgrounds and respond differently to treatment. The Neuropathic Pain Symptom Inventory (NPSI) is able to detect distinct clusters of symptoms (i.e. dimensions) with a putative common mechanistic background. The present study described the psychometric validation of the Portuguese version (PV) of the NPSI.

METHODS

Patients were seen in two consecutive visits, three to four weeks apart. They were asked to: (i) rate their mean pain intensity in the last 24 hours on an 11-point (0-10) numerical scale; (ii) complete the PV-NPSI; (iii) provide the list of pain medications and doses currently in use. VAS and Global Impression of Change (GIC) were filled out in the second visit.

RESULTS

PV-NPSI underwent test-retest reliability, factor analysis, analysis of sensitivity to changes between both visits. The PV-NPSI was reliable in this setting, with a good intra-class correlation for all items. The factorial analysis showed that the PV-NPSI inventory assessed different components of neuropathic pain. Five different factors were found. The PV-NPSI was adequate to evaluate patients with neuropathic pain and to detect clusters of NeP symptoms.

CONCLUSIONS

The psychometric properties of the PV-NPSI rendered it adequate to evaluate patients with both central and peripheral neuropathic pain syndromes and to detect clusters of NeP symptoms.

[What's new in immune-mediated neuropathies?]

Many papers have been published in the field of immune-mediated neuropathies in 2010. Various topics have been covered: diagnostic criteria and clinical forms, pain and its risk factors, clinical evaluation and new immunological markers. Additionally, as nerve biopsy is still useful for evaluating patients with peripheral neuropathy, French and international guidelines have been published. This paper aims to summarize recent discoveries in the field of immune-mediated neuropathies.

Pain in Guillain-Barré syndrome

Evaluation of: Ruts L, Drenthen J, Jongen JL et al. Pain in Guillain-Barré syndrome: a long-term follow-up study. Neurology 75, 1439-1447 (2010). Pain has been recognized as an important symptom of Guillain-Barré syndrome (GBS). The article under review prospectively studied the phenomenon of pain in a cohort of 156 GBS patients for a period of 1 year. It confirmed that pain of significant intensity is relatively common in all subtypes of GBS. It may start before the onset of other symptoms. It correlates with sensory loss, severity of the GBS at its nadir and the presence of diarrhea. In the recovery/chronic stages it correlates with weakness, disability and fatigue. Up to a third of patients have pain at 1 year.