Small fibre neuropathy:

Nonamyloidogenic TTR gene variants c.76G>A and c.337-18G>C are not associated with idiopathic small-fiber neuropathy

BACKGROUND AND PURPOSE

Small-fiber neuropathy (SFN) affects only unmyelinated and thin myelinated fibers. It may be caused by amyloidogenic mutations of the transthyretin (TTR) gene, but not all TTR gene variants are pathogenic. The nonamyloidogenic c.76G>A (rs1800458) and c.337-18G>C (rs36204272) variants of TTR were recently reported to be associated with SFN. We investigated this putative association by analyzing TTR gene sequencing data retrospectively for two cohorts of patients, one with SFN and a control group.

METHODS

In this retrospective single-center study, we analyzed the frequency of the c.76G>A and c.337-18G>C TTR gene variants in a cohort of patients meeting a strict definition of SFN, with or without dysautonomia, a control cohort of patients investigated for nonneurological conditions, and the gnomAD international database.

RESULTS

We included 55 SFN patients in this study, 17 of whom had dysautonomia. The allelic frequencies of the two variants in our cohort of 55 SFN patients were 7.27% for c.76G>A TTR and 5.25% for c.337-18G>C. The frequencies of both variants were statistically similar in the 337 control patients and the gnomAD database.

CONCLUSIONS

The c.76G>A and c.337-18G>C TTR gene variants are not associated with SFN.

[Neuropathy in pruritus medicine : Recommended diagnostics and therapy]

Chronic itch is a frequent and debilitating condition that greatly affects the quality of life of those affected. In a subset of patients, damage to the peripheral or central nervous system constitutes the cause of the itch. Small-fiber neuropathy, nerve compression syndromes, post-herpetic neuralgia, scars and burns are possible conditions affecting the peripheral nervous system potentially causing itch, whereas space-occupying lesions affecting the spinal cord and stroke are examples of conditions that may induce central itch. Neuropathic itch starts on normal appearing skin, is often accompanied by pain sensations and other dysesthesias, and usually relieved by local cold application. Its distribution depends on the affected site of the somatosensory system. A comprehensive medical history is paramount to reach the diagnosis, while complementary diagnostics with skin biopsies for the investigation of cutaneous neuromorphological alterations or medical imaging to rule out nerve impingement may be advised in selected cases. Topical agents such as capsaicin or local anesthetics as well as systemic drugs such as gabapentinoids, antidepressants and opioid receptor modulators are used in the treatment of neuropathic itch. This review article provides an overview of the clinical features, underlying causes, diagnostic workup and therapeutic approach in neuropathic itch.

Cold-evoked potentials in Fabry disease and polyneuropathy

Background

Fabry disease (FD) causes cold-evoked pain and impaired cold perception through small fiber damage, which also occurs in polyneuropathies (PNP) of other origins. The integrity of thinly myelinated fibers and the spinothalamic tract is assessable by cold-evoked potentials (CEPs). In this study, we aimed to assess the clinical value of CEP by investigating its associations with pain, autonomic measures, sensory loss, and neuropathic signs.

Methods

CEPs were examined at the hand and foot dorsum of patients with FD (n = 16) and PNP (n = 21) and healthy controls (n = 23). Sensory phenotyping was performed using quantitative sensory testing (QST). The painDETECT questionnaire (PDQ), FabryScan, and measures for the autonomic nervous system were applied. Group comparisons and correlation analyses were performed.

Results

CEPs of 87.5% of the FD and 85.7% of the PNP patients were eligible for statistical analysis. In all patients combined, CEP data correlated significantly with cold detection loss, PDQ items, pain, and autonomic measures. Abnormal CEP latency in FD patients was associated with an abnormal heart frequency variability item (r = -0.684; adjusted p = 0.04). In PNP patients, CEP latency correlated significantly with PDQ items, and CEP amplitude correlated with autonomic measures (r = 0.688, adjusted p = 0.008; r = 0.619, adjusted p = 0.024). Furthermore, mechanical pain thresholds differed significantly between FD (gain range) and PNP patients (loss range) (p = 0.01).

Conclusions

Abnormal CEPs were associated with current pain, neuropathic signs and symptoms, and an abnormal function of the autonomic nervous system. The latter has not been mirrored by QST parameters. Therefore, CEPs appear to deliver a wider spectrum of information on the sensory nervous system than QST alone.

Detailed clinical, physiological and pathological phenotyping can impact access to disease-modifying treatments in ATTR carriers

BACKGROUND

Hereditary transthyretin amyloidosis is a life-threatening autosomal dominant systemic disease due to pathogenic TTR variants (ATTRv), mostly affecting the peripheral nerves and heart. The disease is characterised by a combination of symptoms, organ involvement and histological amyloid deposition. The available disease-modifying ATTRv treatments (DMTs) are more effective if initiated early. Pathological nerve conduction studies (NCS) results are the cornerstone of large-fibre polyneuropathy diagnosis, but this anomaly occurs late in the disease. We investigated the utility of a multimodal neurological and cardiac evaluation for detecting early disease onset in ATTRv carriers.

METHODS

We retrospectively analysed a cohort of ATTRv carriers with normal NCS results regardless of symptoms. Multimodal denervation and infiltration evaluations included a clinical questionnaire (Lauria and New York Heart Association (NYHA)) and examination, intra-epidermal nerve fibre density assessment, autonomic assessment based on heart rate variability, Sudoscan, meta-iodo-benzyl-guanidine scintigraphy, cardiac biomarkers, echocardiography, MRI and searches for amyloidosis on skin biopsy and bone scintigraphy.

RESULTS

We included 130 ATTRv carriers (40.8% men, age: 43.6±13.5 years), with 18 amyloidogenic TTR gene mutations, the majority of which was the late-onset Val30Met variant (42.3%). Amyloidosis was detected in 16.9% of mutation carriers, including 9 (6.9%) with overt disease (Lauria>2 or NYHA>1) and 13 asymptomatic carriers (10%) with organ involvement (small-fibre neuropathy or cardiomyopathy). Most of these patients received DMT. Abnormal test results of unknown significance were obtained for 105 carriers (80.8%). Investigations were normal in only three carriers (2.3%).

CONCLUSIONS

Multimodal neurological and cardiac investigation of TTRv carriers is crucial for the early detection of ATTRv amyloidosis and initiation of DMT.

Discontinuity third harmonic generation microscopy for label-free imaging and quantification of intraepidermal nerve fibers

Label-free imaging methodologies for nerve fibers rely on spatial signal continuity to identify fibers and fail to image free intraepidermal nerve endings (FINEs). Here, we present an imaging methodology-called discontinuity third harmonic generation (THG) microscopy (dTHGM)-that detects three-dimensional discontinuities in THG signals as the contrast. We describe the mechanism and design of dTHGM and apply it to reveal the bead-string characteristics of unmyelinated FINEs. We confirmed the label-free capability of dTHGM through a comparison study with the PGP9.5 immunohistochemical staining slides and a longitudinal spared nerve injury study. An intraepidermal nerve fiber (IENF) index based on a discontinuous-dot-connecting algorithm was developed to facilitate clinical applications of dTHGM. A preliminary clinical study confirmed that the IENF index was highly correlated with skin-biopsy-based IENF density (Pearson's correlation coefficient R = 0.98) and could achieve differential identification of small-fiber neuropathy (p = 0.0102) in patients with diabetic peripheral neuropathy.

Paradoxical heat sensation as a manifestation of thermal hypesthesia: a study of 1090 patients with lesions of the somatosensory system

ABSTRACT

Paradoxical heat sensation (PHS) is the perception of warmth when the skin is cooled. Paradoxical heat sensation rarely occurs in healthy individuals but more frequently in patients suffering from lesions or disease of the peripheral or central nervous system. To further understand mechanisms and epidemiology of PHS, we evaluated the occurrence of PHS in relation to disease aetiology, pain levels, quantitative sensory testing parameters, and Neuropathic Pain Symptom Inventory (NPSI) items in patients with nervous system lesions. Data of 1090 patients, including NPSI scores from 404 patients, were included in the analysis. We tested 11 quantitative sensory testing parameters for thermal and mechanical detection and pain thresholds, and 10 NPSI items in a multivariate generalised linear model with PHS, aetiology, and pain (yes or no) as fixed effects. In total, 30% of the neuropathic patients reported PHS in contrast to 2% of healthy individuals. The frequency of PHS was not linked to the presence or intensity of pain. Paradoxical heat sensation was more frequent in patients living with polyneuropathy compared with central or unilateral peripheral nerve lesions. Patients who reported PHS demonstrated significantly lower sensitivity to thermal perception, with lower sensitivity to normally painful heat and cold stimuli. Neuropathic Pain Symptom Inventory scores were lower for burning and electric shock-like pain quality for patients with PHS. Our findings suggest that PHS is associated with loss of small thermosensory fibre function normally involved in cold and warm perception. Clinically, presence of PHS could help screening for loss of small fibre function as it is straightforward to measure or self-reported by patients.

Validation of the Body Scan®, a new device to detect small fiber neuropathy by assessment of the sudomotor function: agreement with the Sudoscan®

Background

Sudomotor dysfunction is one of the earliest manifestations of small fiber neuropathy (SFN), reflecting the alteration of sympathetic C fiber innervation of the sweat glands. Among other techniques, such innervation can be assessed by measuring electrochemical skin conductance (ESC) in microsiemens (μS). In this study, ESC was measured at the feet to detect distal SFN. For this objective, the performance of a new device, the Body Scan® (Withings, France), intended for home use, was compared with that of a reference device, the Sudoscan® (Impeto Medical, France), which requires a hospital setting.

Methods

In patients with diabetes with or without neuropathy or non-diabetic patients with lower-limb neuropathy, the diagnostic performance of the Body Scan® measurement was assessed by calculating its sensitivity (Se) and specificity (Sp) to detect at least moderate SFN (Se70 and Sp70), defined by a value of feet ESC ≤ 70 μS and > 50 μS on the Sudoscan® measure, or severe SFN (Se50 and Sp50), defined by a value of feet ESC ≤ 50 μS on the Sudoscan® measure. The agreement between the two devices was assessed with the analysis of Bland-Altman plots, mean absolute error (MAE), and root mean squared error (RMSE) calculations. The repeatability of the measurements was also compared between the two devices.

Results

A total of 147 patients (52% men, mean age 59 years old, 76% diabetic) were included in the analysis. The sensitivity and specificity to detect at least moderate or severe SFN were: Se70 = 0.91 ([0.83, 0.96]), Sp70 = 0.97 ([0.88, 0.99]), Se50 = 0.91 ([0.80, 0.98]), and Sp50 = 0.99 ([0.94, 1]), respectively. The bias and 95% limits of agreement were 1.5 [-5.4, 8.4]. The MAE was 2.9 and the RMSE 3.8. The intra-sample variability was 2.0 for the Body Scan® and 2.3 for the Sudoscan®.

Conclusion

The ESC measurements provided by the Body Scan® were in almost perfect agreement with those provided by the reference device, the Sudoscan®, which validates the accuracy of the Body Scan® for the detection of SFN. By enabling simple, rapid, and autonomous use by the patient at home, this new technique will facilitate screening and monitoring of SFN in daily practice.

Clinical trial registration

ClinicalTrials.gov, identifier NCT05178459.

Peripheral mechanisms of peripheral neuropathic pain

Peripheral neuropathic pain (PNP), neuropathic pain that arises from a damage or disease affecting the peripheral nervous system, is associated with an extremely large disease burden, and there is an increasing and urgent need for new therapies for treating this disorder. In this review we have highlighted therapeutic targets that may be translated into disease modifying therapies for PNP associated with peripheral neuropathy. We have also discussed how genetic studies and novel technologies, such as optogenetics, chemogenetics and single-cell RNA-sequencing, have been increasingly successful in revealing novel mechanisms underlying PNP. Additionally, consideration of the role of non-neuronal cells and communication between the skin and sensory afferents is presented to highlight the potential use of drug treatment that could be applied topically, bypassing drug side effects. We conclude by discussing the current difficulties to the development of effective new therapies and, most importantly, how we might improve the translation of targets for peripheral neuropathic pain identified from studies in animal models to the clinic.

Small fiber neuropathy and intractable scalp pruritus in dermatomyositis patients

Background

Scalp pruritus is a common symptom in Dermatomyositis (DM) patients. There are indications that small nerve fibers neuropathy could be involved in this symptom, however the etiology of scalp pruritus is not fully understood.

Objectives

To assess epidermal nerve fiber (ENF) density of dermatomyositis patients with scalp pruritus by biopsy by confocal microscopy and immunohistochemistry with subsequent imaging analysis.

Methods

DM patients with severe scalp pruritus from the dermatology outpatient clinic were compared to healthy volunteers. Two 4-mm scalp skin biopsies were obtained above the right ear in the parietal region and below the occipital protuberance in the occipital region. Biopsy specimens were incubated with primary antibodies to protein gene product (PGP 9.5), calcitonin gene-related peptide (CGRP), substance P (SP) were used to visualize nerve fibers (ENF) and collagen IV was used to label the epidermal basement membrane. The number of ENFs per millimeter was counted and recorded as the mean of ± SD of counts in 16 images at two micrometer increments/sections, two from each of the samples. ENF densities were compared between groups and a multiple linear regression model was applied to associated factors with ENF density.

Results

Fifteen DM patients with severe scalp pruritus and 12 healthy volunteers were included in the study. The mean number of ENF/mm in occipital region of DM group was 16.0 ± 13.9 while the control group in the same region was 99.8 ± 33.1. In parietal region the number of ENF/mm of DM group was 18.0 ± 20.7 while in control group was 50.4 ± 17.4 (p < 0.001).

Conclusion

DM patients with pruritus could have some impairment of small nerve fiber density that could explain their recalcitrant scalp pruritus.

The applicability of the digit wrinkle scan to quantify sympathetic nerve function

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Normative values for stimulated skin wrinkling are age-dependent.

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Stimulated skin wrinkling has never been evaluated quantitatively.

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The clinical application of the stimulated skin wrinkling in an ordinal fashion is doubtful.

Objective

Stimulated skin wrinkling test (SSW) has been launched as a non-invasive diagnostic procedure. However, no normative age dependent values have been reported that can be applied in clinical practice. The objectives of the study were to (1) collect age-dependent normative values according to the 5-point scale assessment for the SSW, to (2) determine reliability scores for the obtained norm values, and to (3) introduce a new digital method for SSW assessment, the Digit Wrinkle Scan© (DWS©) for detection of wrinkles in a more quantitative manner.

Methods

Firstly, 82 healthy participants were included, divided in 5 age groups. The participants underwent SSW using lidocaine and prilocaine topical cream. Secondly, 35 healthy participants were included to test whether the DWS© could be a novel manner to assess the grade of wrinkling quantitatively. We determined the inter-observer reliability of both methods. Also, the intra-observer reliability was calculated for the DWS©.

Results

We found a decrease in normative values over age. The inter-observer reliability of assessment by the 5-point scale method was moderate after SSW (Cohen’s k: 0.53). Results of the DWS© indicate that total wrinkle length per mm² showed moderate to good agreement for the 4th and 5th digits after SSW, and a low agreement for the other digits.

Conclusions

Age-dependent normative values were obtained according to the 5-point scale, but its clinical application is doubtful since we found a moderate inter-observer reliability. We introduced the DWS© as a possible new method in order to quantify the grade of wrinkling.

Significance

We found unsatisfactory reliability scores, which hampers its usefulness for clinical practice.

Familial episodic pain syndrome: a case report and literature review

The purpose of this case report and literature review is to show that familial episodic pain syndrome (FEPS) is a non-inflammatory genetically inherited pain syndrome. A 3-year-old boy presented at our hospital with pain in both his forearms and lower limbs below the knees for more than 3 years. There were no abnormalities in the blood tests, blood smears, liver and kidney function tests, trace elements tests, cellular immunity test, humoral immunity test, autoantibody tests, C-reactive protein (CRP) test, erythrocyte sedimentation rate (ESR) test, and tumor-related and bone marrow cytology examinations. Additionally, the imaging examination results showed no abnormalities. From the patient's medical history, we found that the mother of the child had a family history of a similar disease. To date, only 21 cases of FEPS3 caused by the sodium voltage-gated channel alpha subunit 11A (SCN11A) gene mutation have been reported. Although the age of onset is different, most of them are inherited in families. The results of the genetic examination revealed that the pain mainly came from the genetic inheritance of the maternal family line. The whole exon gene test revealed that the pain was caused by 2 heterozygous mutations of c.674G > T and c.671T > C in the SCN11A gene.

Skin amyloid deposits and nerve fiber loss as markers of neuropathy onset and progression in hereditary transthyretin amyloidosis

OBJECTIVE

To assess skin biopsy as marker of disease onset and severity in hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN), a treatable disease.

METHODS

In this single center retrospective study, skin Congo red staining and intraepidermal nerve fiber density (IENFD) were evaluated in symptomatic ATTRv-PN patients and asymptomatic TTR gene mutation carriers between 2012 and 2019. Non-ATTRv subjects with small fiber neuropathy suspicion who underwent skin biopsy in the same timespan were used as controls.

RESULTS

One-hundred-eighty-three symptomatic ATTRv-PN, 36 asymptomatic carriers, and 537 non-ATTRv patients were included. Skin biopsy demonstrated amyloid depositions in 80% of the 183 symptomatic cases. Skin amyloid deposits were found in 75% of early-stage ATTRv-PN patients, and in 14% of asymptomatic carriers. All 183 symptomatic and 34/36 asymptomatic patients displayed decreased ankle IENFD with a proximal-distal gradient distribution, and reduced IEFND correlated with disease severity and duration.

CONCLUSIONS

Our study demonstrates skin amyloid deposits are a marker of ATTRv-PN disease onset, and decreased IENFD a marker of disease progression. These results are of major importance for the early identification of ATTRv-PN patients in need of disease-modifying treatments.

Corneal Confocal Microscopy in the Diagnosis of Small Fiber Neuropathy: Faster, Easier, and More Efficient Than Skin Biopsy?

Chronic pain may affect 30–50% of the world’s population and an important cause is small fiber neuropathy (SFN). Recent research suggests that autoimmune diseases may be one of the most common causes of small nerve fiber damage. There is low awareness of SFN among patients and clinicians and it is difficult to diagnose as routine electrophysiological methods only detect large fiber abnormalities, and specialized small fiber tests, like skin biopsy and quantitative sensory testing, are not routinely available. Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible method for quantifying small nerve fiber degeneration and regeneration, and could be an important tool for diagnosing SFN. This review considers the advantages and disadvantages of CCM and highlights the evolution of this technique from a research tool to a diagnostic test for small fiber damage, which can be a valuable contribution to the study and management of autoimmune disease.

Small Fiber Neuropathy in Sarcoidosis

Sarcoidosis (SC) is a granulomatous disease of an unknown origin. The most common SC-related neurological complication is a small fiber neuropathy (SFN) that is often considered to be the result of chronic inflammation and remains significantly understudied. This study aimed to identify the clinical and histological correlates of small fiber neuropathy in sarcoidosis patients. The study was performed in 2018–2019 yy and included 50 patients with pulmonary sarcoidosis (n = 25) and healthy subjects (n = 25). For the clinical verification of the SFN, the “Small Fiber Neuropathy Screening List” (SFN-SL) was used. A punch biopsy of the skin was performed followed by enzyme immunoassay analysis with PGP 9.5 antibodies. Up to 60% of the sarcoidosis patients reported the presence of at least one complaint, and it was possible that these complaints were associated with SFN. The most frequent complaints included dysfunctions of the cardiovascular and musculoskeletal systems and the gastrointestinal tract. A negative, statistically significant correlation between the intraepidermal nerve fiber density (IEND) and SFN-SL score was revealed. In patients with pulmonary sarcoidosis, small fiber neuropathy might develop as a result of systemic immune-mediated inflammation. The most common symptoms of this complication were dysautonomia and mild sensory dysfunction.

Itch in Adult Population with Type 2 Diabetes Mellitus: Clinical Profile, Pathogenesis and Disease-Related Burden in a Cross-Sectional Study

BACKGROUND

Despite growing interest in itch, data regarding itch in type 2 diabetes mellitus (DM2) are still limited, and mostly based on outdated studies. This study aimed to evaluate the clinical characteristics of itch in the adult population with DM2 and explore potential underlying causes.

METHODS

The study group consisted of 109 adult patients with DM2. Standardized questionnaires were completed in order to assess the itch intensity [Numerical Rating Scale (three days, 24hours) (NRS)] and the Four-item Itch Questionnaire (4IIQ) and to assess the psychological impact of itch [ItchyQoL, Six-Item Stigmatization Scale (6-ISS), Hospital Anxiety and Depression Scale (HADS)]. Skin dryness was evaluated clinically and by non-invasive assessment of epidermis moisturizing. Neuropathy was assessed using the clinical Katzenwadel neuropathy scale.

RESULTS

Itch occurred in 35.8% of adult patients with DM2, with NRSmax three days 6.31 ± 2.16 and 8.1 ± 3.5 points in 4IIQ. Itchy patients have had significantly higher FPG levels compared with the non-itchy population (p = 0.01). Patients with itch had a significantly higher possibility of neuropathy compared with non-itchy subjects (p < 0.01). Skin xerosis was significantly more advanced in patients with itch compared to those without (p < 0.01). The mean ItchyQol score was assessed as 41.2 ± 13.4 points, indicating mild life quality impairment and correlated positively with itch intensity. Itchy subjects had significantly higher scores in both anxiety and depression dimensions of HADS (in each p < 0.01).

CONCLUSIONS

We suggest that the primary cause of itch is prolonged poor diabetes control with altered glucose and insulin levels, subsequently causing skin dryness and neuropathy in long-lasting DM2.

Involvement of Cutaneous Sensory Corpuscles in Non-Painful and Painful Diabetic Neuropathy

Distal diabetic sensorimotor polyneuropathy (DDSP) is the most prevalent form of diabetic neuropathy, and some of the patients develop gradual pain. Specialized sensory structures present in the skin encode different modalities of somatosensitivity such as temperature, touch, and pain. The cutaneous sensory structures responsible for the qualities of mechanosensitivity (fine touch, vibration) are collectively known as cutaneous mechanoreceptors (Meissner corpuscles, Pacinian corpuscles, and Merkel cell-axonal complexes), which results are altered during diabetes. Here, we used immunohistochemistry to analyze the density, localization within the dermis, arrangement of corpuscular components (axons and Schwann-like cells), and expression of putative mechanoproteins (PIEZO2, ASIC2, and TRPV4) in cutaneous mechanoreceptors of subjects suffering clinically diagnosed non-painful and painful distal diabetic sensorimotor polyneuropathy. The number of Meissner corpuscles, Pacinian corpuscles, and Merkel cells was found to be severely decreased in the non-painful presentation of the disease, and almost disappeared in the painful presentation. Furthermore, there was a marked reduction in the expression of axonal and Schwann-like cell markers (with are characteristics of corpuscular denervation) as well as of all investigated mechanoproteins in the non-painful distal diabetic sensorimotor polyneuropathy, and these were absent in the painful form. Taken together, these alterations might explain, at least partly, the impairment of mechanosensitivity system associated with distal diabetic sensorimotor polyneuropathy. Furthermore, our results support that an increasing severity of DDSP may increase the risk of developing painful neuropathic symptoms. However, why the absence of cutaneous mechanoreceptors is associated with pain remains to be elucidated.

A Retrospective Analysis of Pain Etiology in Middle-Aged Patients with Peripheral Neuropathy

Background and Objectives: Correct assessment and a multidisciplinary approach appear to be extremely important in preventing peripheral neuropathy and its complications. The purpose of this study was to find the correlations and dissimilarities between different types of peripheral neuropathy, the occurrence of pain, and laboratory results. Materials and Methods: This retrospective study assessed 124 patients who were hospitalized in our neurology department due to various types of sensory or motor disturbances. The patients were eventually diagnosed with peripheral neuropathy, based on the electrophysiological study, anamnesis, physical examination, and laboratory results. The whole group was subjected to statistical analysis. Results: The mean age of patients was over 56 years, with a slight woman predominance. A statistically significant (p < 0.05) relationship between the place of residence and gender was seen, where more men than women live in the rural area, while more women than men live in the urban area. Most often we observed symmetric, sensorimotor, demyelinating, inflammatory, and chronic neuropathy. More than 40% of patients reported pain. A statistically significant correlation between the evolution/severity and the occurrence of pain was seen in subacute type (p < 0.05) and small fibre neuropathy (p < 0.01). Conclusions: A higher incidence of peripheral neuropathy in middle-aged people will become essential in the aging society with lifestyle and chronic disorders. Peripheral neuropathy is slightly more common in women than men and its occurrence may be influenced by work performed or internal and external factors. In the study group, more than 40% of patients reported pain, therefore the pain measurement for each patient should be implemented and repeated at every visit. An assessment of sodium level and, in women, markers of neuroinflammation level in the various types of peripheral neuropathy may be an interesting direction for the future.

PLANTAR SENSATION AND BALANCE IN PATIENTS WITH TYPE 2 DIABETES MELLITUS WITH AND WITHOUT PERIPHERAL NEUROPATHY

The aim of the study was to investigate the effect of diabetes on plantar sense and balance in patients with type 2 diabetes mellitus (T2DM). The study included 300 subjects divided into three groups: 100 T2DM patients with diabetic peripheral neuropathy (group 1); 100 T2DM patients without peripheral neuropathy (group 2); and 100 subjects without DM (group 3). Berg Balance Scale (BBS), Timed Up and Go test (TUG), single leg test with eyes open and closed, and plantar sensory tests were applied in the subjects. Study results showed significant differences in plantar sensory tests, BBS, TUG and single leg test among the three groups (p<0.05). In addition, duration of DM and medication were negatively correlated with single leg test both with eyes open and closed, but showed positive correlation with plantar sense and TUG test. Furthermore, the length of insulin therapy showed positive correlation with plantar sense and TUG test and negative correlation with BBS (p<0.05). In conclusion, DM has an effect on plantar sense and balance, and there is a relation between the duration of DM and balance problems. Balance problems are observed more often in patients with neuropathy.

Associations of Small Fiber Neuropathy with Geriatric Nutritional Risk Index and Arterial Stiffness in Hemodialysis

BACKGROUND

Peripheral neuropathy is a common neurological complication in uremic patients, and quantitative sensory testing (QST) is effective for diagnosis of small fiber neuropathy. Malnutrition and arterial stiffness are prevalent in patients undergoing hemodialysis (HD). The associations of small fiber neuropathy with nutritional status and arterial stiffness remain uncertain in maintenance HD patients.

METHODS

A total of 152 HD patients were included. Geriatric nutritional risk index (GNRI), an indicator of nutritional status, was calculated by serum albumin and actual and ideal body weight. Arterial stiffness was defined as brachial-ankle pulse wave velocity (baPWV) > 1400 cm/s. Small fiber neuropathy was assessed by an abnormal QST threshold of cold and warm sensation in patients' hands or feet. Multivariate forward logistic regression analysis was performed to examine the associations among abnormal QST threshold, GNRI, and arterial stiffness.

RESULTS

baPWV and prevalence of abnormal QST threshold were significantly higher in diabetic patients. Multivariate logistic analyses revealed that older age (OR, 1.081; 95% CI, 1.026-1.139, p = 0.003) and male gender (OR, 4.450; 95% CI, 1.250-15.836, p = 0.021) were associated with abnormal warm threshold of hands. Furthermore, diabetes (OR, 3.966; 95% CI, 1.351-11.819, p = 0.012) and lower GNRI (per 1 unit increase, OR, 0.935, 95% CI, 0.887-0.985, p = 0.012) were associated with abnormal cold threshold of feet. Arterial stiffness (OR, 5.479, 95% CI, 1.132-22.870, p = 0.020) and higher calcium-phosphorus product (OR, 1.071, 95% CI, 1.013-1.132, p = 0.015) were associated with abnormal warm threshold of feet.

CONCLUSIONS

Lower GNRI and arterial stiffness were significantly associated with small fiber neuropathy in patients undergoing HD. Malnutrition risk and vascular factors might play important roles in small fiber neuropathy among patients undergoing HD.

Neuropathic Itch: Routes to Clinical Diagnosis

Neuropathic itch occurs due to damage of neurons of the peripheral or central nervous system. Several entities, including metabolic, neurodegenerative, orthopedic, infectious, autoimmune, malignant, and iatrogenic conditions, may affect the somatosensory system and induce neuropathic itch. Due to the complex nature of neuropathic itch, particularly concerning its clinical presentation and possible etiological factors, diagnostic work-up of this condition is challenging. A detailed medical history, especially in regard to the itch, and a comprehensive physical examination are relevant to detect characteristic signs and symptoms of neuropathic itch and to rule out other possible causes for chronic itch. Complementary diagnostic exams, especially laboratory tests, determination of the intraepidermal nerve fiber density via a skin biopsy and radiological examinations may be indicated to confirm the diagnosis of neuropathic itch and to identify underlying etiological factors. Functional assessments such as quantitative sensory testing, nerve conduction studies, evoked potentials, or microneurography may be considered in particular cases. This review article provides a comprehensive overview of the diagnostic work-up recommended for patients with neuropathic itch.

Advances in imaging technologies for the assessment of peripheral neuropathies in rheumatoid arthritis

Peripheral neuropathy in patients with rheumatoid arthritis is associated with a maladaptive autoimmune response that may cause chronic pain and disability. Nerve conduction studies are the routine method performed when rheumatologists presume its presence. However, this approach is invasive, may not reveal subtle malfunctions in the early stages of the disease, and does not expose abnormalities in structures surrounding the nerves and muscles, limiting the possibility of a timely diagnosis. This work aims to present a narrative review of new technologies for the clinical assessment of peripheral neuropathy in Rheumatoid Arthritis. Through a bibliographic search carried out in five repositories, from 1990 to 2020, we identified three technologies that could detect peripheral nerve lesions and perform quantitative evaluations: (1) magnetic resonance neurography, (2) functional magnetic resonance imaging, and (3) high-resolution ultrasonography of peripheral nerves. We found these tools can overcome the main constraints imposed by the previous electrophysiologic methods, enabling early diagnosis.

Advances in the Management of Small Fiber Neuropathy

Small fiber neuropathy (SFN) is a prevalent neurologic syndrome. Testing methods have emerged in recent years to better diagnose it, including autonomic tests and skin punch biopsy. SFN can present in a non-length-dependent fashion and can be mistaken for syndromes such as fibromyalgia and complex regional pain syndrome. SFN is caused by a variety of metabolic, infectious, genetic, and inflammatory diseases. Recently treatments have emerged for TTR amyloid neuropathy and Fabry disease, and novel biomarkers have been found both in genetic and inflammatory SFN syndromes. Ongoing trials attempt to establish the efficacy of intravenous immunoglobulin in inflammatory SFN syndromes.

Oxaliplatin- and docetaxel-induced polyneuropathy: clinical and neurophysiological characteristics

The aim of this study was to evaluate the presence and characterization of chemotherapy-induced neuropathy (CIPN) and neuropathic pain 5 years after adjuvant chemotherapy with docetaxel or oxaliplatin. Patients from an ongoing prospective study, who had received adjuvant chemotherapy with docetaxel or oxaliplatin in 2011 to 2012 were invited to participate. The patients underwent a thorough examination with interview, neurological examination, questionnaires, assessment tools, nerve conduction studies (NCS), quantitative sensory testing, MScan motor unit number estimation (MUNE), and corneal confocal microscopy (CCM). Patients were divided into no, possible, probable, and confirmed CIPN. Out of the 132 eligible patients, 63 agreed to participate: 28 had received docetaxel and 35 had received oxaliplatin. Forty-one percent had confirmed CIPN, 34% possible or probable CIPN, and 22% did not have CIPN. The CIPN was characterized mainly by sensory nerve fiber loss, with a more pronounced large fiber than small fiber loss but also some motor fiber loss identified on NCS and MUNE. In general, patients had mild neuropathy with relatively low scores on assessment tools and no association with mood and quality of life. CCM was not useful as a diagnostic tool. Of the patients with probable or confirmed CIPN, 30% experienced pain, which was most often mild, but still interfered moderately with daily life in 20% to 25% and was associated with lower quality of life. In conclusion CIPN was confirmed in 41% 5 years after chemotherapy. The neuropathy was generally mild, but in patients with neuropathic pain it was associated with lower quality of life.

Diagnostic criteria for idiopathic small fiber neuropathy: A systematic review

Idiopathic small fiber neuropathy (iSFN) lacks broadly accepted diagnostic criteria, which hinders its timely diagnosis and treatment. A systematic literature review was performed to assess the published screening and diagnostic criteria for iSFN, excluding studies where SFN was of well-established etiology. Eighty-four clinical studies and seven guideline/review publications were included in this systematic review. Substantial heterogeneity existed in iSFN diagnostic criteria. The most common set of criteria to diagnose iSFN [presence of any symptoms of iSFN, absence of large fiber involvement, and reduced intraepidermal nerve fiber density (IENFD)] was used in only 14% of studies. Mandatory individual criteria to confirm iSFN included any sensory symptoms (60% of studies), pain (19% of studies), small fiber signs (20% of studies), absence of large fiber signs (62% of studies), reduced IENFD (38% of studies), and autonomic symptoms (1% of studies). This review highlights a clear need for standardized, evidence-based guidelines for diagnosing iSFN.

Diagnosing peripheral neuropathy in South-East Asia: A focus on diabetic neuropathy

Burning and stabbing pain in the feet and lower limbs can have a significant impact on the activities of daily living, including walking, climbing stairs and sleeping. Peripheral neuropathy in particular is often misdiagnosed or underdiagnosed because of a lack of awareness amongst both patients and physicians. Furthermore, crude screening tools, such as the 10-g monofilament, only detect advanced neuropathy and a normal test will lead to false reassurance of those with small fiber mediated painful neuropathy. The underestimation of peripheral neuropathy is highly prevalent in the South-East Asia region due to a lack of consensus guidance on routine screening and diagnostic pathways. Although neuropathy as a result of diabetes is the most common cause in the region, other causes due to infections (human immunodeficiency virus, hepatitis B or C virus), chronic inflammatory demyelinating polyneuropathy, drug-induced neuropathy (cancer chemotherapy, antiretrovirals and antituberculous drugs) and vitamin deficiencies (vitamin B1 , B6 , B12 , D) should be actively excluded.

Diabetic neuropathy: A focus on small fibres

Diabetic peripheral neuropathy (DPN) is diagnosed too late, which contrasts with our approach for diabetic retinopathy and nephropathy, where incipient disease is detected early enabling timely treatment. The 10-g monofilament and a foot exam are the commonly used methods for screening diabetic neuropathy, but this primarily identifies moderate to severe diabetic neuropathy. Small fibres are damaged early and are associated with the development of painful diabetic neuropathy, foot ulceration, and Charcot foot. Tests of small fibre damage include thermal thresholds, microneurography, evoked potentials, sudomotor function, laser Doppler flare, skin biopsy, and corneal confocal microscopy. Measures of small fibre damage and repair may be key to the assessment of efficacy in clinical trials of disease modifying therapies for diabetic neuropathy.

Generalized chronic itch induced by small-fibre neuropathy: clinical profile and proposed diagnostic criteria

BACKGROUND

Small-fibre neuropathy (SFN) is a known cause for pain, however, it may be also associated with chronic itch. The clinical profile of chronic itch due to SFN is poorly defined and accordingly under-diagnosed in clinical care.

OBJECTIVES

To establish the clinical profile of patients with SFN and to propose diagnostic criteria for this patient population.

METHODS

Clinical data from patients diagnosed with SFN [chronic generalized itch and reduced intraepidermal nerve fibre density (IENFD)] were analysed retrospectively.

RESULTS

A total of 142 patients (60 females, median age: 62.5 years) were included. Patients reported daily, moderate to severe itch intensity scores occurring mostly in attacks (62.5%). Only 11 patients experienced exclusively itch, while the remaining patients (92%) reported pruralgia (itch along with painful sensations). Burning (50%), a sensation like needle pricks (46%) and tingling (45%) were the sensory symptoms reported by most patients. Cold or ice application led to an alleviation of the symptoms. The IENFD did not correlate with itch intensity; however, patients with a severely reduced IENFD (<30% of the normative cut-off value) reported more frequently sharp, spiky and drilling sensations compared to the remaining patients. The quality of life was moderately impaired and correlated with itch intensity, whereas anxiety and depression scores were low.

CONCLUSIONS

Onset of pruralgia on normal appearing skin, occurrence in attacks and symptomatic alleviation with cold/ice application should alert physicians for a possible neuropathic SFN-related origin of itch. A reduced IENFD can confirm the diagnosis of SFN.

Small Fiber Neuropathy: Clinicopathological Correlations

Small fiber neuropathy develops due to the selective damage of the thin fibers of peripheral nerves. Many common diseases can cause this condition, including diabetes, infections, autoimmune and endocrine disorders, but it can occur due to genetic alterations, as well. Eighty-five skin biopsy-proven small-fiber neuropathy cases were analyzed. Forty-one (48%) cases were idiopathic; among secondary types, hypothyreosis (9.4%), diabetes mellitus (7%), cryoglobulinemia (7%), monoclonal gammopathy with unproved significance (4.7%), Sjögren's disease (3%), and paraneoplastic neuropathy (3%) were the most common causes. Two-thirds (68%) of the patients were female, and the secondary type started 8 years later than the idiopathic one. In a vast majority of the cases (85%), the distribution followed a length-dependent pattern. Intraepidermal fiber density was comparable in idiopathic and secondary forms. Of note, we found significantly more severe pathology in men and in diabetes. Weak correlation was found between patient-reported measures and pathology, as well as with neuropathic pain-related scores. Our study confirmed the significance of small fiber damage-caused neuropathic symptoms in many clinical conditions, the gender differences in clinical settings, and pathological alterations, as well as the presence of severe small fiber pathology in diabetes mellitus, one of the most common causes of peripheral neuropathy.

Intraepidermal Nerve Fiber Density in Postmortem Skin: A Novel Approach

OBJECTIVE

To determine the feasibility of examining intraepidermal nerve fiber density (IENFD) in postmortem skin.

METHODS

From 12 subjects, 3-mm skin punch biopsies were collected 1-4 days postmortem from the proximal leg and distal leg, with a mean (range) interval from the death of 37 (15-91) hours. Causes of death varied broadly, including hepatocellular carcinoma, chronic lymphocytic leukemia, generalized atherosclerosis, progressive supranuclear palsy, Parkinson disease, emphysema, and obesity. The mean (range) number of sections evaluated from each biopsy was 5.08 (2-6) from the proximal leg and 5.92 (5-6) from the distal leg. Sections were stained with PGP 9.5 for blinded counting using bright field microscopy. Qualitative and quantitative assessment of feasibility included a comparison of fiber staining with that in healthy subjects and mean IENFD in postmortem samples. Interobserver reliability was assessed among 3 blinded raters by calculating intraclass correlation coefficients and percentage variability of IENFD in at least 4 sections from biopsies in 5 healthy subjects.

RESULTS

Intraobserver and interobserver correlation coefficients of blinded IENFD counts undertaken by 4 authors were consistently >0.80, and the coefficient of variation was ≤10%. The quality of staining in postmortem samples was comparable with that in healthy subjects and was not substantially affected by time from death to specimen collection of up to nearly 4 days. Mean (range) IENFD from postmortem samples in the proximal and distal leg was 2.73 (0-7.65) and 1.93 (0-4.91) fibers/mm of skin, respectively. Two of 3 patients who had received chemotherapy during life showed a nearly complete absence of intraepidermal nerve fibers.

CONCLUSIONS

IENFD measurement in postmortem skin is feasible and may be used to study the epidemiology of SFN.

Painful and non-painful diabetic polyneuropathy: Clinical characteristics and diagnostic issues

Diabetic neuropathy (DN) is a common complication of diabetes and can be either painful or non-painful. It is challenging to diagnose this complication, as no biomarker or clear consensus on the clinical definition of either painful or non-painful DN exists. Hence, a hierarchical classification has been developed categorizing the probability of the diagnosis into: possible, probable or definite, based on the clinical presentation of symptoms and signs. Pain is a warning signal of tissue damage, and non-painful DN therefore represents a clinical and diagnostic challenge because it often goes unnoticed until irreversible nerve damage has occurred. Simple clinical tests seem to be the best for evaluation of DN in the general care for diabetes. Screening programs at regular intervals might be the most optimal strategy for early detection and interventions to possibly prevent further neuronal damage and to lower the economic burden of this complication.

Bilaterally Reduced Intraepidermal Nerve Fiber Density in Unilateral CRPS-I

Objective

Findings regarding small nerve fiber damage in complex regional pain syndrome type I (CRPS-I) are not uniform, and studies have not included a matched healthy control group. The aim was to assess intraepidermal nerve fiber density (IENFD) in relation to thermal sensitivity of the same skin areas in CRPS-I patients and a gender- and age-matched healthy control group.

Methods

IENFD was investigated in skin biopsies from the CRPS-affected and contralateral limbs of eight CRPS-I patients and from an equivalent site in eight gender- and age-matched healthy controls (HCs). Thermal thresholds (cold/warm detection, cold- and heat-pain detection) were assessed on the affected limb, the matching contralateral limb, and on the equivalent limbs of HCs, and participants rated the intensity of cold/heat and pain to static thermal stimuli (5 °C and 40 °C).

Results

IENFD was significantly lower in both the affected and contralateral limbs of CRPS-I patients than HCs, but IENFD did not differ between the affected and contralateral limbs of patients. The heat pain threshold was lower in the affected CRPS-I limb than in HCs, but all other thermal thresholds were similar in both groups. CRPS-I patients rated the cold stimulus as colder and more painful in the affected limb, and the warm stimulus as hotter, bilaterally, than the HCs.

Conclusions

CRPS-I may be associated with bilateral small fiber damage, and perhaps small fiber neuropathy and bilateral disturbances in thermo-sensory perception. These disturbances could stem from a systemic response to injury or might increase the risk of developing CRPS-I after physical trauma.

Small-fiber neuropathy definition, diagnosis, and treatment

In the last 30 years, improvement of diagnostic methods enabled routine evaluation of small A-delta and C nerve fibers impairment, which results with the clinical condition known as a small-fiber neuropathy (SFN). This syndrome develops as a result of metabolic, toxic, immune-mediated, or genetic factors. The main clinical features include neuropathic pain and autonomic disturbance, which are occasionally disclaimed due to outstanding fatigue, daily performance decline, anxiety, and depression. As clinical, neurological, nerve conduction, and electromyography studies are commonly normal, diagnosis often depends on the finding of decreased intra-epidermal density of nerve fibers, per skin biopsy. This review highlights the etiology, clinical, diagnostic aspects, and SFN treatment.

The Clinical Features of Painful Small-Fiber Neuropathy Suggesting an Origin Linked to Primary Sjögren's Syndrome

OBJECTIVE

We attempted to determine whether clinical features could differentiate painful small-fiber neuropathy related to primary Sj€ogren's syndrome (pSS-SFN) from idiopathic SFN (idio-SFN).

METHODS

Validated clinical questionnaires and neurophysiological investigations specific for pain and SFN assessment were performed in 25 patients with pSS-SFN and 25 patients with idio-SFN.

RESULTS

Patients with idio-SFN had more frequent severe burning sensations and higher mean anxiety scores and daily pain intensity compared to patients with pSSSFN. Conversely, patients with pSS-SFN had reduced electrochemical skin conductance measured by Sudoscan_, and almost half of them had the sensation of walking on cotton wool.

CONCLUSION

Our results suggest that idio-SFN more specifically involved small sensory fibers than pSS-SFN, in which subtle dysfunction of larger sensory fibers and damage of distal autonomic sudomotor innervation may occur. A practical algorithm is proposed to help to differentiate SFN associated with pSS from idio-SFN, based on information very easy to obtain by clinical interview.

A new look at painful diabetic neuropathy

The prevalence of diabetes mellitus and its chronic complications continue to increase alarmingly. Consequently, the massive expenditure on diabetic distal symmetrical polyneuropathy (DSPN) and its sequelae, will also likely rise. Up to 50% of patients with diabetes develop DSPN, and about 20% develop neuropathic pain (painful-DSPN). Painful-DSPN can cast a huge burden on sufferers' lives with increased rates of unemployment, mental health disorders and physical co-morbidities. Unfortunately, due to limited understanding of the mechanisms leading to painful-DSPN, current treatments remain inadequate. Recent studies examining the pathophysiology of painful-DSPN have identified maladaptive alterations at the level of both the peripheral and central nervous systems. Additionally, genetic studies have suggested that patients with variants of voltage gated sodium channels may be more at risk of developing neuropathic pain in the presence of a disease trigger such as diabetes. We review the recent advances in genetics, skin biopsy immunohistochemistry and neuro-imaging, which have the potential to further our understanding of the condition, and identify targets for new mechanism based therapies.

Changes in intraepidermal nerve fiber and Langerhans cell densities in the plantar skin of rats after mercuric chloride exposure

Mercury and its compounds possess strong neurotoxicity and patients with mercury poisoning often report pain and numbness in the distal extremities that conform to the "stocking-glove" pattern. However, no study has investigated whether damage to small nerve fibers is associated with mercury poisoning. The aims of the present study were to evaluate the effects of different doses of mercury chloride (HgCl₂ ) on intraepidermal nerve fibers density (IENFD) and Langerhans cells (LCs) in the plantar skin of rats and to assess the possible relationship between changes in IENFD and sensory testing. Male Sprague-Dawley rats were divided into three experimental groups and administered HgCl₂ solutions via gavage at three different doses (4.25, 8.5, and 17 mg/kg/day) for 21 days. Subsequently, behavioral tests and pathological changes in IENFD and LCs were assessed at three different time points (1, 2, and 3 weeks). Rats in all three HgCl₂ groups exhibited varying degrees of weight and hair loss. Thermal hypersensitivity was evident in all the HgCl₂ groups (for middle-2w subgroup, p < 0.05). Mechanical sensitivity tests revealed hyposensitivity in all the HgCl₂ groups except the high-1w subgroup. Significant decreases in IENFD (for the high-1w, middle-1w, low-2w, and low-3w subgroups, p < 0.05) and significant increases in the density of LCs (except for the low-1w and high-2w subgroups, all p < 0.05) were found in all groups after HgCl₂ exposure. An association analysis revealed a significant correlation between the decrease in IENFD and the increase in LCs densities (r = -0.573, p < 0.01). The present study demonstrated a decrease in IENFD and an increase in LCs density in the plantar skin of rats after HgCl₂ poisoning, indicating that damage of the small nerve fibers occurs after mercury poisoning.

Distinct TrkA and Ret modulated negative and positive neuropathic behaviors in a mouse model of resiniferatoxin-induced small fiber neuropathy

Neurotrophic factors and their corresponding receptors play key roles in the maintenance of different phenotypic dorsal root ganglion (DRG) neurons, the axons of which degenerate in small fiber neuropathy, leading to various neuropathic manifestations. Mechanisms underlying positive and negative symptoms of small fiber neuropathy have not been systematically explored. This study investigated the molecular basis of these seemingly paradoxical neuropathic behaviors according to the profiles of TrkA and Ret with immunohistochemical and pharmacological interventions in a mouse model of resiniferatoxin (RTX)-induced small fiber neuropathy. Mice with RTX neuropathy exhibited thermal hypoalgesia and mechanical allodynia, reduced skin innervation, and altered DRG expression profiles with decreased TrkA(+) neurons and increased Ret(+) neurons. RTX neuropathy induced the expression of activating transcription factor 3 (ATF3), and ATF3(+) neurons were colocalized with Ret but not with TrkA (P<0.001). As a neuroprotectant, 4-Methylcatechol (4MC) promoted skin reinnervation partially with correlated reversal of the neuropathic behaviors and altered neurochemical expression. Gambogic amide, a selective TrkA agonist, normalized thermal hypoalgesia, and GW441756, a TrkA kinase inhibitor, induced thermal hypoalgesia, which was already reversed by 4MC. Mechanical allodynia was reversed by a Ret kinase inhibitor, AST487, which induced thermal hyperalgesia in naïve mice. The activation of Ret signaling by XIB4035 induced mechanical allodynia and thermal hypoalgesia in RTX neuropathy mice in which the neuropathic behaviors were previously normalized by 4MC. Distinct neurotrophic factor receptors, TrkA and Ret, accounted for negative and positive neuropathic behaviors in RTX-induced small fiber neuropathy, respectively: TrkA for thermal hypoalgesia and Ret for mechanical allodynia and thermal hypoalgesia.

Depletion of nerve growth factor in chemotherapy-induced peripheral neuropathy associated with hematologic malignancies

Objective

To investigate whether the depletion of nerve growth factor (NGF) is associated with the development of chemotherapy-induced peripheral neuropathy (CIPN) in patients with hematologic malignancy.

Methods

We prospectively enrolled hematologic cancer patients who had a plan to receive bortezomib, thalidomide, or vincristine. Baseline NGF levels were measured within one week before the start date of chemotherapy. Follow-up NGF levels were measured after four months from the start date of chemotherapy or the date when CIPN was initially diagnosed.

Results

Baseline and follow-up NGF pairs were measured in 45 patients (male/female = 27/18, median age = 63 years old). CIPN has developed in 28 patients. In the CIPN group, the level of NGF was significantly decreased after chemotherapy compared to the baseline (△NGF = −3.52 ±5.72; p-value = 0.003), while the NGF level of the no-CIPN group was not changed after chemotherapy. The differences in △NGF levels between the CIPN and no-CIPN group were more profound when analyzed in the subgroup of newly diagnosed multiple myeloma patients (△NGF = −4.14 ± 4.87 pg/ml for the CIPN group and +2.52 ± 8.39 pg/ml for the no-CIPN group; p-value = 0.043).

Conclusions

This study shows that the depletion of NGF occurs during the development of CIPN, suggesting pathogenesis based on the role of NGF and therapeutic implications.

Symptom profiles in the painDETECT Questionnaire in patients with peripheral neuropathic pain stratified according to sensory loss in quantitative sensory testing

The painDETECT Questionnaire (PDQ) is commonly used as a screening tool to discriminate between neuropathic pain (NP) and nociceptive pain, based on the self-report of symptoms, including pain qualities, numbness, and pain to touch, cold, or heat. However, there are minimal data about whether the PDQ is differentially sensitive to different sensory phenotypes in NP. The aim of the study was to analyze whether the overall PDQ score or its items reflect phenotypes of sensory loss in NP as determined by quantitative sensory testing. An exploratory analysis in the Innovative Medicines Initiative Europain and Neuropain database was performed. Data records of 336 patients identified with NP were grouped into sensory profiles characterized by (1) no loss of sensation, (2) loss of thermal sensation, (3) loss of mechanical sensation, and (4) loss of thermal and mechanical sensation. painDETECT Questionnaire profiles were analyzed in a 2-factor analysis of variance. Patients with loss of thermal sensation (2 and 4) significantly more often reported pain evoked by light touch, and patients with loss of mechanical sensation (3 and 4) significantly more often reported numbness and significantly less often burning sensations and pain evoked by light touch. Although the PDQ was not designed to assess sensory loss, single items reflect thermal and/or mechanical sensory loss at group level, but because of substantial variability, the PDQ does not allow for individual allocation of patients into sensory profiles. It will be useful to develop screening tools according to the current definition of NP.

Intraepidermal Nerve Fiber Density: Diagnostic and Therapeutic Relevance in the Management of Chronic Pruritus: a Review

In recent years, measurement of the intraepidermal nerve fiber (IENF) density has gained relevance in the diagnostics of chronic pruritus. This method allows the objectification and quantification of a small-fiber neuropathy, which may manifest clinically with pruritus, pain or dysesthetic sensory symptoms, such as burning, stinging and tingling sensations or numbness. Upon suspicion of a small-fiber neuropathy as a cause for chronic pruritus, targeted diagnostic procedures are essential for the early detection of the neuroanatomical changes. After a punch biopsy of the lower leg, the obtained tissue undergoes an immunofluorescence staining process with a primary antibody against the protein gene product 9.5. The IENFs can thus be detected and are quantified according to pre-determined guidelines based on an international consensus. In addition to morphological changes, functional impairment of small-fibers can be assessed using quantitative sensory testing by assessing detection and pain thresholds of various thermal and mechanic modalities. This method, however, is time-consuming and requires a specialized investigator, and thus it is not routinely used in the diagnostic investigation of chronic pruritus. Diagnosing a small-fiber neuropathy underlying chronic pruritus has therapeutic relevance. If possible, the underlying cause of the neuropathy should be treated. Alternatively, symptomatic therapy options include topical (capsaicin) and systemic (anticonvulsants and/or antidepressants) agents. Chronification processes may lead to refractory pruritus, and thus treatment should be initiated as soon as possible. The aim of this review is to present and discuss the measurement of the IENF density as a diagnostic tool and its role in the management of patients with chronic pruritus. A brief case report is presented to better illustrate the role of this diagnostic method in the clinical setting.

A painful neuropathy-associated Nav1.7 mutant leads to time-dependent degeneration of small-diameter axons associated with intracellular Ca2+ dysregulation and decrease in ATP levels

Small fiber neuropathy is a painful sensory nervous system disorder characterized by damage to unmyelinated C- and thinly myelinated Aδ- nerve fibers, clinically manifested by burning pain in the distal extremities and dysautonomia. The clinical onset in adulthood suggests a time-dependent process. The mechanisms that underlie nerve fiber injury in small fiber neuropathy are incompletely understood, although roles for energetic stress have been suggested. In the present study, we report time-dependent degeneration of neurites from dorsal root ganglia neurons in culture expressing small fiber neuropathy-associated G856D mutant Nav1.7 channels and demonstrate a time-dependent increase in intracellular calcium levels [Ca2+]i and reactive oxygen species, together with a decrease in ATP levels. Together with a previous clinical report of burning pain in the feet and hands associated with reduced levels of Na+/K+-ATPase in humans with high altitude sickness, the present results link energetic stress and reactive oxygen species production with the development of a painful neuropathy that preferentially affects small-diameter axons.