Studying serum neurofilament light chain levels as a potential new biomarker for small fiber neuropathy.

BACKGROUND AND PURPOSE: Diagnosing small fiber neuropathies can be challenging. To address this issue, whether serum neurofilament light chain (sNfL) could serve as a potential biomarker of damage to epidermal Aδ- and C-fibers was tested. METHODS: Serum NfL levels were assessed in 30 patients diagnosed with small fiber neuropathy and were compared to a control group of 19 healthy individuals. Electrophysiological studies, quantitative sensory testing and quantification of intraepidermal nerve fiber density after skin biopsy were performed in both the proximal and distal leg. RESULTS: Serum NfL levels were not increased in patients with small fiber neuropathy compared to healthy controls (9.1 ± 3.9 and 9.4 ± 3.8, p = 0.83) and did not correlate with intraepidermal nerve fiber density at the lateral calf or lateral thigh or with other parameters of small fiber impairment. CONCLUSION: Serum NfL levels cannot serve as a biomarker for small fiber damage.

Nociceptive two-point discrimination acuity and body representation failure in polyneuropathy.

OBJECTIVES: Although patients' complaints suggest polyneuropathy (PNP) and neuropathic pain, routine investigations do not always support the diagnosis. Assessing two-point-pain discrimination thresholds (2ptDT) and quantify body representation disturbances might be useful to close this diagnostic gap. METHODS: Pinprick pain and laser-heat pain perception thresholds and 2ptDT on hands, forearms, lower legs and feet were obtained in 20 PNP patients (mean age: 57.6 ± 13.9) and 20 healthy subjects (mean age: 50.6 ± 4.7 years). Body representation disturbances were assessed by self-estimating feet size and the Bath CRPS body perception disturbances questionnaire adapted for PNP. RESULTS: Pain perception thresholds and laser-heat pain 2ptDT were unaltered, but patients had higher pinprick pain 2ptDT then the healthy subjects. The 2ptDT for pinprick at the hands discriminate best between groups (U-test; p=0.001). Furthermore, patients estimated their feet longer than they are. In subsequent multivariate discriminant analyses, 2ptDT for pinprick pain at the hands, 2ptDT for laser-heat pain and the perception thresholds for laser-heat pain at the feet classified 85% of PNP vs. HC correctly. The combination of 2ptDT for pinprick pain at the hands, pinprick pain perception thresholds at the calves and foot length estimation differentiates painful vs. non-painful PNPs correctly in 90% of the cases. CONCLUSIONS: Testing 2ptDT for painful pinprick stimuli at the hands and asking for foot length estimation might add to diagnostic accuracy in painful PNP.

Substance P Serum Degradation in Complex Regional Pain Syndrome - Another Piece of the Puzzle?

In a previous study, we demonstrated that the serum peptidase system might be less efficient in complex regional pain syndrome (CRPS). Since the neuropeptide substanc P (SP) contributes to inflammation in CRPS, we now investigated the metabolism of SP in CRPS specifically. An SP metabolism assay was performed in 24 CRPS patients, which constitute a subgroup of our previous investigation on BK degradation. In addition, we included 26 healthy controls (24 newly recruited plus 2 from our previous investigation), and 13 patients after limb trauma, who did not fulfil the CRPS diagnostic criteria (trauma controls, TC) were included. We adapted a thin layer chromatography assay (TLC) to quantify SP disappearance after incubation with 7.5 µL of serum. These results were compared with bradykinin (BK) metabolization to BK1-8 and BK1-5 fragments from our previous study. In addition, TC were clinically and quantitative sensory testing (QST) phenotyped; the phenotyping of CRPS patients was retrieved from our existing database. SP metabolism was less efficient in CRPS and TC patient serum vs human control (HC) serum (P < .03) suggesting reduced activity of the neutral endopeptidase (NEP) and/or the angiotensin converting enzyme (ACE). Together with the decreased occurrence of BK1-5 fragment in CRPS and TC, this suggests a reduced activation of the angiotensin converting enzyme (ACE). There was no clear clinical phenotype related to impaired SP degradation; duration of disease and gender were also not associated. Most importantly, results in TC did not differ from CRPS. Collectively, our current and previous experimental results suggest that limb trauma reduces serum peptidase metabolism of SP ex vivo, specifically serum ACE activity. However, this finding is not CRPS-specific and seems to be rather a long-term consequence of the trauma itself. PERSPECTIVE: The experimental data from this study further support the hypothesis that impaired metabolism of inflammatory peptides potentially contribute to the development of posttraumatic pain in CRPS or limb trauma patients.

Pain, disability, and lifestyle: Patients with complex regional pain syndrome compared to chronic musculoskeletal pain-A retrospective analysis.

BACKGROUND: Complex regional pain syndrome (CRPS) is an orphan disease occurring as a complication after trauma. Due to its acute onset and the typical clinical presentation of the inflammatory and autonomous signs, it is an eye-catching chronic pain disease affecting also young and working people. In social media and the internet, high pain severity and the unfavourable prognosis are often empathized. METHODS: Here, we compared epidemiological, pain and lifestyle factors of 223 CPRS patients from the "ncRNAPain" cohort with 255 patients with chronic musculoskeletal pain (MSK). MSK patients were recruited at the beginning of a multimodal pain therapy programme. We searched for factors predicting pain intensity. RESULTS: Both chronic pain diseases affected women in middle age. Patients with MSK were more obese, drank more alcohol, and were less educated (Pearson chi-square Test or Mann-Whitney/U-Test). Both groups smoked more than healthy people in the OECD (Organization for Economic Cooperation and Development). Mann-Whitney/U-Test confirmed that CRPS patients did not have more severe pain and did not suffer more from pain-related disability than patients with MSK. CRPS patients also had less psychiatric comorbidities. Multiple linear regression analysis revealed that group assignment, depressive characteristics, body mass index, average alcohol consumption and smoking predicted higher pain ratings, while disease duration, anxiety symptoms or gender had no influence on pain intensity. CONCLUSION: In summary, our study supports a more optimistic view on pain in CRPS patients in comparison to MSK and identifies lifestyle factors that might contribute to the pathophysiology like smoking and drinking. Important next steps are the identification of CRPS patients at risk for chronification or-vice versa-with protective factors for pain resolution. SIGNIFICANCE: This study compares complex regional pain syndrome (CRPS) and chronic musculoskeletal pain and questions previously reported pain, disability and lifestyle factors associated with CRPS.

Reduced serum protease activity in Complex Regional Pain Syndrome: The impact of angiotensin-converting enzyme and carboxypeptidases.

Complex Regional Pain Syndrome (CRPS) occurs in about 2% of patients after fracture of the limbs. In an earlier clinical study with 102 probands we have shown that the serum protease network in CRPS might be less effective. Based on these results we hypothesized that angiotensin-converting enzyme (ACE) and carboxypeptidase N (CPN) activity contribute to the differences of labeled bradykinin (DBK) degradation by patients' sera. Details of the enzymatic processes remained however unclear. The contributions of ACE and CPN in the serum degradation of DBK were studied using specific inhibitors. CPN1-ELISA was performed in serum. It was confirmed that the majority of DBK was degraded by ACE and CPN. The data delivered proof that the ACE serum activity was lowered in CRPS. High-resolution mass spectrometry was additionally used for protein expression analysis of sera of above study cohort (CRPS vs. healthy probands). According to principal component analysis of these data, significant differences between CRPS and control samples only occurred in sera of females younger than 46 years. In these CRPS patients, a number of defence / immunity-related proteins and members of the renin-angiotensin system (RAS) protein network were regulated. The impact of CPN in CRPS pathophysiology is subject to further investigation. The data support the hypothesis that both the RAS and the innate immune system might be affected in CRPS. A database of regulated serum proteins was established for future research.

Systemic inflammatory biomarkers in painful diabetic neuropathy.

OBJECTIVES: We conducted a systematic review of the literature with meta-analysis to determine whether painful diabetic neuropathy is associated with a specific inflammatory profile. METHODS: The study is based on the PRISMA statement for systematic reviews. We performed a search of published studies up until January 2021 in MEDLINE and Web of Science based on heading and free text terms. The search strategy included the phrases: diabetic peripheral neuropathy, painful peripheral neuropathy individually and in combination with the terms: inflammation and inflammatory biomarkers. We screened titles and abstracts and performed data extraction. We also manually searched the article titles in the reference lists of key studies and reviews published in the last 20 years. DATA EXTRACTION: Data extracted from the studies included study design, inclusion and exclusion criteria, sample type including serum and plasma, source of the sample including patients with peripheral diabetic neuropathy or patients with painful and painless neuropathy of any etiology. Blood concentrations of all measured cytokines were recorded. Whenever possible we calculated the effect size and confidence interval. Non-human studies were excluded from the meta-analysis. RESULTS: Thirteen studies were included in this meta-analysis. The study design was cross-sectional, case control or cohort type studies. Specific inflammatory mediators are significantly higher in painful than in painless diabetic neuropathy as well as in painful neuropathies of any etiology. Markers of inflammation are also increased in those patients with diabetes mellitus, who suffer from peripheral neuropathy in comparison to patients with diabetes mellitus but no signs of peripheral neuropathy. A proinflammatory state may be the common denominator of pain and peripheral neuropathy in patients with diabetes mellitus but the inflammatory profiles seem to differ.

Local and Systemic Expression Pattern of MMP-2 and MMP-9 in Complex Regional Pain Syndrome.

Matrix metalloproteinases (MMP)-2 and MMP-9 play important roles in inflammation as well as in pain processes. For this reason, we compared the concentrations of these enzymes in skin and serum of patients with complex regional pain syndrome (CRPS), other pain diseases and healthy subjects. We analyzed ipsi- and contralateral skin biopsies of 18 CRPS patients, as well as in 10 pain controls and 9 healthy subjects. Serum samples were analyzed from 20 CRPS, 17 pain controls and 17 healthy subjects. All samples were analyzed with ELISA. Concentrations were then compared to clinical data as well as to quantitative sensory testing data.MMP-2 was increased in both ipsi- and contralateral skin biopsies of CRPS patients compared to healthy subjects. While low ipsilateral MMP-2 was associated with trophic changes, contralateral MMP-2 inversely correlated with the CRPS severity. MMP-9 was also locally increased in ipsilateral CRPS skin, and higher ipsi- and contralateral MMP-9 levels correlated with CRPS severity. We conclude that MMP-2 and MMP-9 are differently expressed depending on the clinical phenotype in CRPS. PERSPECTIVE: This article describes an upregulation of MMPs in CRPS and pain controls and shows different expression of MMP-2 and -9 depending on clinical phenotype in CRPS. These results provide evidence that MMP-2 and -9 play a key role in CRPS pathophysiology.

Chance or challenge, spoilt for choice? New recommendations on diagnostic and therapeutic considerations in hereditary transthyretin amyloidosis with polyneuropathy: the German/Austrian position and review of the literature.

Hereditary transthyretin amyloidosis is caused by pathogenic variants (ATTRv) in the TTR gene. Alongside cardiac dysfunction, the disease typically manifests with a severely progressive sensorimotor and autonomic polyneuropathy. Three different drugs, tafamidis, patisiran, and inotersen, are approved in several countries, including the European Union and the United States of America. By stabilizing the TTR protein or degrading its mRNA, all types of treatment aim at preventing amyloid deposition and stopping the otherwise fatal course. Therefore, it is of utmost importance to recognize both onset and progression of neuropathy as early as possible. To establish recommendations for diagnostic and therapeutic procedures in the follow-up of both pre-symptomatic mutation carriers and patients with manifest ATTRv amyloidosis with polyneuropathy, German and Austrian experts elaborated a harmonized position. This paper is further based on a systematic review of the literature. Potential challenges in the early recognition of disease onset and progression are the clinical heterogeneity and the subjectivity of sensory and autonomic symptoms. Progression cannot be defined by a single test or score alone but has to be evaluated considering various disease aspects and their dynamics over time. The first-line therapy should be chosen based on individual symptom constellations and contra-indications. If symptoms worsen, this should promptly implicate to consider optimizing treatment. Due to the rareness and variability of ATTRv amyloidosis, the clinical course is most importantly directive in doubtful cases. Therefore, a systematic follow-up at an experienced center is crucial to identify progression and reassure patients and carriers.

Follow-up in transthyretin familial amyloid polyneuropathy: Useful investigations.

Patients with transthyretin amyloid polyneuropathy (TTR-FAP) and asymptomatic mutation-carriers have to be regularly followed-up in order to identify disease progression and the time point for starting or modifying therapy. In this case series we describe the potential suitability of different variables as progression markers. We retrospectively analyzed the follow-up charts of 10 TTR-FAP patients. Clinical examination included the Neuropathy Impairment Score of Lower Limb (NIS-LL), temperature perception thresholds, nerve conduction and autonomic function tests. The NIS-LL had the greatest value for a sensitive and correct follow-up for all TTR-FAP stages. All other examinations provided useful additional information but they were either less suited for advanced TTR-FAP, or had a higher test-retest variability. The results of this study provide preliminary evidence that a good clinical investigation is mandatory in TTR-FAP follow-up. Simple neuropathy scores like the NIS-LL might be as useful as technical investigations for TTR-FAP follow-up.

Clinical phenotypes and classification algorithm for complex regional pain syndrome.

OBJECTIVE: We pursued the hypothesis that complex regional pain syndrome (CRPS) signs observed by neurologic examination display a structure allowing for alignment of patients to particular phenotype clusters. METHODS: Clinical examination data were obtained from 3 independent samples of 444, 391, and 202 patients with CRPS. The structure among CRPS signs was analyzed in sample 1 and validated with sample 2 using hierarchical clustering. For patients with CRPS in sample 3, an individual phenotype score was submitted to k-means clustering. Pain characteristics, quantitative sensory testing, and psychological data were tested in this sample as descriptors for phenotypes. RESULTS: A 2-cluster structure emerged in sample 1 and was replicated in sample 2. Cluster 1 comprised minor injury eliciting CRPS, motor signs, allodynia, and glove/stocking-like sensory deficits, resembling a CRPS phenotype most likely reflecting a CNS pathophysiology (the central phenotype). Cluster 2, which consisted of edema, skin color changes, skin temperature changes, sweating, and trophic changes, probably represents peripheral inflammation, the peripheral phenotype. In sample 3, individual phenotype scores were calculated as the sum of the mean values of signs from each cluster, where signs from cluster 1 were coded with 1 and from cluster 2 with -1. A k-means algorithm separated groups with 78, 36, and 88 members resembling the peripheral, central, and mixed phenotypes, respectively. The central phenotype was characterized by cold hyperalgesia at the affected limb. CONCLUSIONS: Statistically determined CRPS phenotypes may reflect major pathophysiologic mechanisms of peripheral inflammation and central reorganization.

Sensory profiles and immune-related expression patterns of patients with and without neuropathic pain after peripheral nerve lesion.

In this multicenter cross-sectional study, we determined sensory profiles of patients with (NL-1) and without neuropathic pain (NL-0) after nerve lesion and assessed immune-related systemic gene expression. Patients and matched healthy controls filled in questionnaires and underwent neurological examination, neurophysiological studies, quantitative sensory testing, and blood withdrawal. Neuropathic pain was present in 67/95 (71%) patients (NL-1). Tactile hyperalgesia was the most prominent clinical sign in NL-1 patients (P < 0.05). Questionnaires showed an association between neuropathic pain and the presence of depression, anxiety, and catastrophizing (P < 0.05 to P < 0.01). Neuropathic pain was frequently accompanied by other chronic pain (P < 0.05). Quantitative sensory testing showed ipsilateral signs of small and large fiber impairment compared to the respective contralateral side, with elevated thermal and mechanical detection thresholds (P < 0.001 to P < 0.05) and lowered pressure pain threshold (P < 0.05). Also, more loss of function was found in patients with NL-1 compared to NL-0. Pain intensity was associated with mechanical hyperalgesia (P < 0.05 to P < 0.01). However, quantitative sensory testing did not detect or predict neuropathic pain. Gene expression of peptidylglycine α-amidating monooxygenase was higher in NL patients compared with healthy controls (NL-1, P < 0.01; NL-0, P < 0.001). Also, gene expression of tumor necrosis factor-α was higher in NL-1 patients compared with NL-0 (P < 0.05), and interleukin-1ß was higher, but IL-10 was lower in NL-1 patients compared with healthy controls (P < 0.05 each). Our study reveals that nerve lesion presents with small and large nerve fiber dysfunction, which may contribute to the presence and intensity of neuropathic pain and which is associated with a systemic proinflammatory pattern.

The serum protease network-one key to understand complex regional pain syndrome pathophysiology.

Complex regional pain syndrome (CRPS) develops after fracture. The acute CRPS phenotype resembles exaggerated inflammation, which is explained by local and systemic activation of a proinflammatory network including peptides and cytokines. Epidemiologic data suggest that inactivation of the peptidase angiotensin-converting enzyme in patients treated for hypertension increases the odds to develop CRPS. This hint leads us to investigate the serum protease network activity in patients with CRPS vs respective controls. For this purpose, we developed a dabsyl-bradykinin (DBK)-based assay and used it to investigate patients with CRPS, as well as healthy and pain (painful diabetic neuropathy [dPNP]) controls. The major result is that the degradation of DBK to fragments 1-8 and 1-5 in healthy control and dPNP is shifted to higher values for DBK1-8 and lower values for DBK1-5 at 1 hour of incubation in patients with CRPS. Using this novel reporter peptide assay, we have been able to show that the resolving protease network for mediators such as BK might be different in patients with CRPS; having a look at the clinical signs, which resemble inflammation, this resolving protease network is probably less effective in CRPS.

Transthyretin familial amyloid polyneuropathy (TTR-FAP): Parameters for early diagnosis.

Background: Familial transthyretin amyloidosis is a life-threatening disease presenting with sensorimotor and autonomic polyneuropathy. Delayed diagnosis has a detrimental effect on treatment and prognosis. To facilitate diagnosis, we analyzed data patterns of patients with transthyretin familial amyloid polyneuropathy (TTR-FAP) and compared them to polyneuropathies of different etiology for clinical and electrophysiological discriminators. Methods: Twenty-four patients with TTR-FAP and 48 patients with diabetic polyneuropathy (dPNP) were investigated (neurological impairment score NIS; neurological disability score NDS) in a cross-sectional design. Both groups were matched for gender and presence of pain. Quantitative sensory testing (QST), sympathetic skin response (SSR), heart rate variability (HRV), and nerve conduction studies (NCV) were performed. Both groups were compared using univariate analysis. In a stepwise discriminant analysis, discriminators between both neuropathies were identified. These discriminators were validated comparing TTR-FAP patients with a cohort of patients with chemotherapy-induced polyneuropathy (CIN) and chronic inflammatory demyelinating neuropathy (CIDP). Results: TTR-FAP patients scored higher in NDS and NIS and had impaired cold detection (CDT, p = .024), cold-warm discrimination (TSL, p = .019) and mechanical hyperalgesia (MPT, p = .029) at the hands, SSR (upper limb, p = .022) HRV and ulnar and sural NCS (all p < .05) were more affected in TTR-FAP. Ulnar nerve sensory NCV, CDT, and the MPT but not the other parameters discriminated TTR-FAP from dPNP (82% of cases), from CIN (86.7%) and from CIDP (68%; only ulnar sNCV). Conclusion: Low ulnar SNCV, impaired cold perception, and mechanical hyperalgesia at the hands seem to characterize TTR-FAP and might help to differentiate from other polyneuropathies.

[Neurological or interdisciplinary outpatient pain treatment: comparison of treatment success and satisfaction]. / Neurologische oder interdisziplinäre Schmerzambulanz: Vergleich des Behandlungserfolges und der Zufriedenheit.

The aim of this study was to compare the satisfaction and success of treatment for pain patients who were interdisciplinary (anaesthesiological, psychosomatic, neurological, orthopedic) treated or underwent neurological care alone. Methods We selected 183 patients who were treated in our neurological clinic and in our interdisciplinary pain management center (IST). Of these, 142 patients having polyneuropathy, headache or muskuloskelettal pain were included in the final analysis. 39 patients (27.5 %) were treated in the IST and 103 patients were treated exclusively by a neurologist. These patients were asked to complete a questionnaire, and were queried about the satisfaction and pain parameters. Results The neurological and multidisciplinary pain treatment led to a similar improvement in pain (p < 0.001). This effect was independent of the underlying disease. The interdisciplinary outpatient treatment resulted not primarily in an increased patient satisfaction. Conclusions The reduction of pain and patient satisfaction of neurological outpatient pain treatment were comparable with those of a multidisciplinary outpatient therapy. The only significant advantage of the interdisciplinary treatment was lower hospitalization rate after therapy. This result cannot evaluate the efficiency of inpatient or day hospital pain management, but suggests that in many cases a neurological outpatient pain therapy is sufficient, so that neurological outpatient care should be promoted.

Bone Trauma Causes Massive but Reversible Changes in Spinal Circuitry.

Bone fracture with subsequent immobilization of the injured limb can cause complex regional pain syndrome (CRPS) in humans. Mechanisms of CRPS are still not completely understood but bone fracture with casting in mice leads to a similar post-traumatic inflammation as seen in humans and might therefore be an analog to human CRPS. In this article we report behavioral and spinal electrophysiological changes in mice that developed swelling of the paw, warming of the skin, and pain in the injured limb after bone fracture. The receptive field sizes of spinal neurons representing areas of the hind paws increased after trauma and recovered over time-as did the behavioral signs of inflammation and pain. Interestingly, both sides-the ipsi- and the contralateral limb-showed changes in mechanical sensitivity and neuronal network organization after the trauma. The characteristics of evoked neuronal responses recorded in the dorsal horn of the mice were similar between uninjured controls and fractured animals. However, we saw a caudal extension of the represented area of the hind paw in the spinal cord at the injured side and an occurrence of large receptive fields of wide dynamic range neurons. The findings in mice compare with human symptoms in CRPS with ipsi- and also contralateral allodynia and pain. In all mice tested, all signs subsided 12 weeks after trauma. Our data suggest a significant reorganization of spinal circuitry after limb trauma, in a degree more comprehensive than most models of neuropathies. This process seems to be reversible in the rodent. PERSPECTIVE: The discovery of enlarged spinal neuronal receptive fields and caudal extension of the representation area of the injured body part, which subsides several weeks after a bone trauma in mice, might give hope to patients of CRPS if-in the future-we are able to translate the rodent recovery mechanisms to post-traumatic humans.