Levodopa, methylmalonic acid, and neuropathy in idiopathic Parkinson disease

Parkinson's disease and vitamins: a focus on vitamin B12

Parkinson's disease (PD) has been linked to a vast array of vitamins among which vitamin B12 (Vit B12) is the most relevant and often investigated specially in the context of intrajejunal levodopa infusion therapy. Vit B12 deficiency, itself, has been reported to cause acute parkinsonism. Nevertheless, concrete mechanisms through which B12 deficiency interacts with PD in terms of pathophysiology, clinical manifestation and progression remains unclear. Recent studies have suggested that Vit B12 deficiency along with the induced hyperhomocysteinemia are correlated with specific PD phenotypes characterized with early postural instability and falls and more rapid motor progression, cognitive impairment, visual hallucinations and autonomic dysfunction. Specific clinical features such as polyneuropathy have also been linked to Vit B12 deficiency specifically in context of intrajejunal levodopa therapy. In this review, we explore the link between Vit B12 and PD in terms of physiopathology regarding dysfunctional neural pathways, neuropathological processes as well as reviewing the major clinical traits of Vit B12 deficiency in PD and Levodopa-mediated neuropathy. Finally, we provide an overview of the therapeutic effect of Vit B12 supplementation in PD and posit a practical guideline for Vit B12 testing and supplementation.

Large-fiber neuropathy in Parkinson's disease: a narrative review

BACKGROUND

Numerous studies reported a higher prevalence of polyneuropathy (PNP) in patients with Parkinson's disease (PD) compared to the general population. Importantly, PNP symptoms can aggravate both motor and sensory disturbances in PD patients and negatively impact the disease course. Recent analyses indicate distinct PNP patterns in PD.

MAIN TEXT

This review aims to provide an overview of the current insights into etiological factors, diagnostic methods, and management strategies of large fiber neuropathy in PD. Despite the higher prevalence, the causes of PNP in PD are still not fully understood. A genetic predisposition can underlie PNP onset in PD. Main research attention is focused on long-term levodopa exposure which is suggested to increase PNP risk by depletion of methylation cofactors such as vitamin B12 and accumulation of homocysteine that altogether can alter peripheral nerve homeostasis. Beyond a potential "iatrogenic" cause, alpha-synuclein deposition has been detected in sural nerve fibers that could contribute to peripheral neuronal degeneration as part of the systemic manifestation of PD. Whereas mild axonal sensory PNP predominates in PD, a considerable proportion of patients also show motor and upper limb nerve involvement. Intriguingly, a correlation between PNP severity and PD severity has been demonstrated. Therefore, PNP screening involving clinical and instrument-based assessments should be implemented in the clinical routine for early detection and monitoring. Given the etiological uncertainty, therapeutic or preventive options remain limited. Vitamin supplementation and use of catechol-O-methyltransferase-inhibitors can be taken into consideration.

CONCLUSION

PNP is increasingly recognized as a complicating comorbidity of PD patients. Long-term, large-scale prospective studies are required to elucidate the causative factors for the development and progression of PD-associated PNP to optimize treatment approaches. The overall systemic role of "idiopathic" PNP in PD and a putative association with the progression of neurodegeneration should also be investigated further.

Longitudinal evaluation of polyneuropathy in Parkinson's disease

BACKGROUND

Increasing evidence indicates a higher prevalence of polyneuropathy (PNP) in Parkinson's disease (PD). However, the involvement of large fiber neuropathy in PD still remains poorly understood. Given the lack of longitudinal data, we investigated the course of PNP associated with PD.

METHODS

In total, 41 PD patients underwent comprehensive clinical evaluation including motor and non-motor assessments as well as nerve conduction studies at baseline and at 2 years of follow-up. The definition of PNP was based on electrophysiological standard criteria. Common causes of PNP were excluded.

RESULTS

At baseline, PNP was diagnosed in 65.85% of PD patients via electroneurography. Patients with PNP presented with higher age (p = 0.019) and PD motor symptom severity (UPDRS III; p < 0.001). Over the course of 2 years, PNP deteriorated in 21.95% of cases, and 26.83% remained without PNP. Deterioration of nerve amplitude was most prevalent in the median sensory nerve affecting 57.58% of all PD cases with an overall reduction of median sensory nerve amplitude of 45.0%. With regard to PD phenotype, PNP progression was observed in 33.33% of the tremor dominant and 23.81% of the postural instability/gait difficulties subtype. Decrease of sural nerve amplitude correlated with lower quality of life (PDQ-39, p = 0.037) and worse cognitive status at baseline (MoCA, p = 0.042).

CONCLUSION

The study confirms the high PNP rate in PD, and demonstrates a significant electrophysiological progression also involving nerves of the upper extremities. Longitudinal studies with larger cohorts are urgently needed and should elucidate the link between PD and PNP with the underlying pathomechanisms.

Association between pain threshold and manifested pain assessed using a PD-specific pain scale in Parkinson's disease

Background

The neurodegenerative process in Parkinson's disease (PD) affects both dopaminergic and non-dopaminergic structures, which determine the wide range of motor and non-motor symptoms (NMS), including different types of pain. Diverse mechanisms contribute to pain in PD. Abnormal nociceptive processing is considered a distinctive feature of the disease.

Objective

In the present study, we used a validated PD-specific pain assessment tool to investigate self-reported pain in PD patients and to analyze the association with the objective pain threshold.

Methods

The RIII component of the nociceptive flexor reflex was assessed in 35 patients with PD and was compared to 40 healthy controls. Self-reported pain was measured using the Bulgarian version of the King's Parkinson's Disease Pain Scale (KPPS-BG). A correlation analysis was used to investigate the relationship between the objective nociceptive threshold and PD pain as assessed by KPPS-BG.

Results

PD patients had a significantly lower RIII threshold than control individuals (the mean SD value was 6.24 ± 1.39 vs. 10.33 ± 1.64) when assessed in the "off" state. A statistically significant (p < 0.05) fairly negative Spearman's correlation was observed between the decreased spinal nociceptive threshold and fluctuation-related pain (-0.31). Domain 4, "nocturnal pain" (-0.21), and the KPPS-BG total score (-0.21) showed a weak negative correlation. An insignificant positive correlation was found between domain 6-"discoloration, edema/swelling"-and the RIII threshold. A higher Movement Disorders Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score and modified Hoehn and Yahr (H&Y) scale are associated with a decreased nociceptive flexor reflex threshold.

Conclusion

The results of the present study demonstrate the important role of increased spinal nociception in the occurrence of pain, which is associated with fluctuations and, to a lesser extent, nocturnal pain.

Imbalance and Falls in Patients with Parkinson's Disease: Causes and Recent Developments in Training and Sensor-Based Assessment

Imbalance and falls in patients with Parkinson's disease (PD) do not only reduce their quality of life but also their life expectancy. Aging-related symptoms as well as disease-specific motor and non-motor symptoms contribute to these conditions and should be treated when appropriate. In addition to an active lifestyle, advanced exercise training is useful and effective, especially for less medically responsive symptoms such as freezing of gait and postural instability at advanced stages. As treadmill training in non-immersive virtual reality, including dual tasks, significantly reduced the number of falls in PD patients, the mechanism(s) explaining this effect should be further investigated. Such research could help to select the most suitable patients and develop the most effective training protocols based on this novel technology. Real-life digital surrogate markers of mobility, such as those describing aspects of endurance, performance, and the complexity of specific movements, can further improve the quality of mobility assessment using wearables.

The vicious circle between homocysteine, methyl group-donating vitamins and chronic levodopa intake in Parkinson's disease

A biomarker for declined methylation capacity is elevation of homocysteine levels. They increase the risk for onset of vascular disease and contribute to progression of chronic neurodegeneration and aging. This narrative review discusses associations between homocysteine, consumption of methyl group-donating vitamins and impact on disease-generating mechanisms in levodopa-treated patients with Parkinson's disease. We conclude to recommend levodopa-treated patients to substitute themselves with methyl group-donating vitamins. This is harmless in terms of application of folic acid, methylcobalamin or hydroxocobalamin. Moreover, we suggest a crucial discussion on the value of the various popular hypotheses on Parkinson's disease-generating mechanisms. Findings from studies with acute levodopa exposure describe oxidative stress generation and impaired methylation capacity, which causes gene dysfunction. Their repeated occurrences contribute to onset of mitochondrial dysfunction, iron enrichment and pathologic protein accumulation in the long term. Current research underestimates these epigenetic, metabolic consequences of chronic levodopa application. Supplementary treatment strategies are recommended to avoid levodopa-related side effects.

The association between methylmalonic acid, a biomarker of mitochondrial dysfunction, and cause-specific mortality in Alzheimer's disease and Parkinson's disease

Background

Alzheimer's disease (AD) and Parkinson's disease (PD) are the leading causes of death among the elderly. Recent research has demonstrated that mitochondrial dysfunction, which is hallmark of neurodegenerative diseases, is a contributor to the development of these diseases.

Methods and materials

Methylmalonic acid (MMA), AD, PD, inflammatory markers and covariates were extracted from the National Health and Nutrition Examination Survey (NHANES). The classification of the inflammatory markers was done through quartile conversion. A restricted cubic spike function was performed to study their dose-response relationship. MMA subgroups from published studies were used to explore the correlation between different subgroups and cause-specific mortality. Multivariable weighted Cox regression was carried out to investigate MMA and cause-specific mortality in patients with AD and PD. Weighted survival analysis was used to study the survival differences among MMA subgroups.

Results

A non-linear correlation was observed between MMA and AD-specific death and PD-specific mortality. The presence of MMA Q4 was linked to increased death rates among AD patients (HR = 6.39, 95%CI: 1.19-35.24, P = 0.03) after controlling for potential confounders in a multivariable weighted Cox regression model. In PD patients, the MMA Q4 (Q4: HR: 5.51, 95 % CI: 1.26-24, P = 0.02) was also related to increased mortality. The results of survival analysis indicated that the poorer prognoses were observed in AD and PD patients with MMA Q4.

Conclusion

The higher level of mitochondria-derived circulating MMA was associated with a higher mortality rate in AD and PD patients. MMA has the potential to be a valuable indicator for evaluating AD and PD patients' prognosis in the clinic.

Integrative analysis of gene expression profiles of substantia nigra identifies potential diagnosis biomarkers in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease whose etiology is attributed to development of Lewy bodies and degeneration of dopaminergic neurons in the substantia nigra (SN). Currently, there are no definitive diagnostic indicators for PD. In this study, we aimed to identify potential diagnostic biomarkers for PD and analyzed the impact of immune cell infiltrations on disease pathogenesis. The PD expression profile data for human SN tissue, GSE7621, GSE20141, GSE20159, GSE20163 and GSE20164 were downloaded from the Gene Expression Omnibus (GEO) database for use in the training model. After normalization and merging, we identified differentially expressed genes (DEGs) using the Robust rank aggregation (RRA) analysis. Simultaneously, DEGs after batch correction were identified. Gene interactions were determined through venn Diagram analysis. Functional analyses and protein-protein interaction (PPI) networks were used to the identify hub genes, which were visualized through Cytoscape. A Lasso Cox regression model was employed to identify the potential diagnostic genes. The GSE20292 dataset was used for validation. The proportion of infiltrating immune cells in the samples were determined via the CIBERSORT method. Sixty-two DEGs were screened in this study. They were found to be enriched in nerve conduction, dopamine (DA) metabolism, and DA biosynthesis Gene Ontology (GO) terms. The PPI network and Lasso Cox regression analysis revealed seven potential diagnostic genes, namely SLC18A2, TAC1, PCDH8, KIAA0319, PDE6H, AXIN1, and AGTR1, were subsequently validated in peripheral blood samples obtained from healthy control (HC) and PD patients, as well as in the GSE20292 dataset. The results revealed the exceptional sensitivity and specificity of these genes in PD diagnosis and monitoring. Moreover, PD patients exhibited a higher number of plasma cells, compared to HC individuals. The SLC18A2, TAC1, PCDH8, KIAA0319, PDE6H, AXIN1, and AGTR1 are potential diagnostic biomarkers for PD. Our findings also reveal the essential roles of immune cell infiltration in both disease onset and trajectory.

Homocysteine, vitamin B metabolites, dopamine-substituting compounds, and symptomatology in Parkinson's disease: clinical and therapeutic considerations

Emerging studies suggest a correlation between elevated plasma homocysteine (hcy) levels and the risk of atherosclerosis, vascular disorders, and neurodegenerative diseases, including Parkinson's disease (PD). This narrative review delves into the intricate relationships between Hcy, vitamin B metabolites, dopamine-substituting compounds, and various symptoms of PD. Patients undergoing a long-term L-dopa/dopa-decarboxylase inhibitor (DDI) regimen, especially without a concurrent catechol-O-methyl transferase (COMT) inhibitor or methyl group-donating vitamin supplementation, such as vitamins B6 and B12, exhibit an elevation in Hcy and a decline in vitamin B metabolites. These altered concentrations appear to be associated with heightened risks of developing non-motor symptoms, including peripheral neuropathy and cognitive disturbances. The review underscores the impact of levodopa metabolism via COMT on homocysteine levels. In light of these findings, we advocate for the supplementation of methyl group-donating vitamins, notably B6 and B12, in patients undergoing a high-dose L-dopa/DDI regimen, particularly those treated with L-dopa/carbidopa intestinal gel (LCIG) infusion.

Oral and intestinal dysbiosis in Parkinson's disease

The suspicion of an origin of Parkinson's disease (PD) at the periphery of the body and the involvement of environmental risk factors in the pathogenesis of PD have directed the attention of the scientific community towards the microbiota. The microbiota represents all the microorganisms residing both in and on a host. It plays an essential role in the physiological functioning of the host. In this article, we review the dysbiosis repeatedly demonstrated in PD and how it influences PD symptoms. Dysbiosis is associated with both motor and non-motor PD symptoms. In animal models, dysbiosis only promotes symptoms in individuals genetically susceptible to Parkinson's disease, suggesting that dysbiosis is a risk factor but not a cause of Parkinson's disease. We also review how dysbiosis contributes to the pathophysiology of PD. Dysbiosis induces numerous and complex metabolic changes, resulting in increased intestinal permeability, local and systemic inflammation, production of bacterial amyloid proteins that promote α-synuclein aggregation, as well as a decrease in short-chain fatty acid-producing bacteria that have anti-inflammatory and neuroprotective potential. In addition, we review how dysbiosis decreases the efficacy of dopaminergic treatments. We then discuss the interest of dysbiosis analysis as a biomarker of Parkinson's disease. Finally, we give an overview of how interventions modulating the gut microbiota such as dietary interventions, pro-biotics, intestinal decontamination and fecal microbiota transplantation could influence the course of PD.

Vitamin B₁₂ deficiency and Parkinson’s disease

Parkinson’s disease (PD) is a progressive neurodegenerative disease with various clinical manifestations, its origin not always can be explained only by dopamine deficiency. Long-term treatment with levodopa (especially its intraduodenal administration), as well as clinical manifestations of polyneuropathy, cognitive deficits, postural disorders with freezing of gate, REM sleep behavioral disorders, are more often associated with vitamin B12 deficiency. Several reasons for this association and mechanisms of their development are discussed. Early detection of cobalamin deficiency in PD, especially in patients from high-risk groups, makes it possible to stop this pathological condition timely and prevent irreversible changes. Modern data on the use of high-dose (1000 μ g) oral vitamin B12 are presented, it has comparable clinical efficacy and significant advantages, compared with the parenteral form, in terms of the ease of use and the ability to avoid undesirable postinjection reactions.

Chaudhuri's Dashboard of Vitals in Parkinson's syndrome: an unmet need underpinned by real life clinical tests

We have recently published the notion of the "vitals" of Parkinson's, a conglomeration of signs and symptoms, largely nonmotor, that must not be missed and yet often not considered in neurological consultations, with considerable societal and personal detrimental consequences. This "dashboard," termed the Chaudhuri's vitals of Parkinson's, are summarized as 5 key vital symptoms or signs and comprise of (a) motor, (b) nonmotor, (c) visual, gut, and oral health, (d) bone health and falls, and finally (e) comorbidities, comedication, and dopamine agonist side effects, such as impulse control disorders. Additionally, not addressing the vitals also may reflect inadequate management strategies, leading to worsening quality of life and diminished wellness, a new concept for people with Parkinson's. In this paper, we discuss possible, simple to use, and clinically relevant tests that can be used to monitor the status of these vitals, so that these can be incorporated into clinical practice. We also use the term Parkinson's syndrome to describe Parkinson's disease, as the term "disease" is now abandoned in many countries, such as the U.K., reflecting the heterogeneity of Parkinson's, which is now considered by many as a syndrome.

Proton pump inhibitor use and the risk for Parkinson's disease: A nationwide population-based study in Taiwan

Previous studies have shown that proton pump inhibitors (PPIs) are associated with an increased risk of dementia. However, little is known about the relationship between PPIs use and Parkinson's disease (PD). This study aimed to examine whether PPI use was associated with an increased risk of developing clinically verified PD. This used data from the Taiwan National Health Insurance Research Database for the period between 1999 and 2011, and patients with PPI use were compared with 1 to 1 propensity score-matched controls by age, sex, cohort entry year, and comorbidity. A multivariate analysis was performed using Cox proportional hazards models to estimate the association between PPI use and PD risk. Subgroup analyses according to sex, age, and comorbidities were also conducted. In total, 56,785 PPI users and 56,785 matched controls were enrolled in this study. In the PPI cohort, 366 patients developed PD during a median follow-up of 5.0 years. The incidence rate of PD was 1.48-fold higher in PPI users than in non-PPI users (90.0 vs 133.2 per 100,000 person-years), with an adjusted hazard ratio of 1.76 (95% confidence interval, 1.48-2.08). In the subgroup analysis, the adjusted risk of PD in the PPI and non-PPI cohorts increased in the subgroups regardless of age, sex, and comorbidities. The results of this retrospective, nationwide, population-based cohort study in Taiwan indicate that PPI use is associated with the risk of PD development. Further mechanistic studies on the effect of PPI on PD are needed.

Levodopa, homocysteine and Parkinson's disease: What's the problem?

Elevated circulating homocysteine levels have been associated with cognitive impairment and cardio-cerebro-vascular events. Levodopa treatment of Parkinson's disease tends to further elevate circulating homocysteine levels due to the metabolism of levodopa via catechol-O-methyltransferase (COMT). COMT co-factors are vitamins B12, B6 and folic acid. Accumulating deficiencies of these vitamins are presumed to be the substrate for the homocysteine elevation. B-vitamin therapy reduces homocysteine levels. This begs the question of whether Parkinson's disease patients on levodopa should be concurrently treated with ongoing B-vitamin therapy (versus long-term monitoring of B-vitamins/homocysteine). There is a substantial literature on this topic that has accumulated over the last quarter-century, and this topic is still debated. This review summarizes the relevant literature with the aim of approximating closure on this issue. Also, noteworthy is that Parkinson's disease patients with renal insufficiency may not tolerate cyanocobalamin, the standard oral B12 supplement due to facilitation of renal decline; alternatives are discussed.

An umbrella review of systematic reviews with meta-analysis on the role of vitamins in Parkinson's disease

INTRODUCTION

This umbrella review aimed to systematically review the available literature and assess the association of dietary intake or serum levels of different vitamins and the risk of PD, to help find out more efficient treatments for PD patients by replenishing the deficiency of vitamins.

METHODS

Pubmed/Medline, Scopus, Google Scholar and hand searching bibliographies of retrieved articles in duplicate, were used to detect all relevant meta-analyses investigating the relationship between vitamins and PD. After study selection, data were extracted from previously published meta-analyses and pooled by Review Manager version 5.4 and CMA software version 2.2.064 to achieve effect sizes. Level of statistical significance was set at P ≤ 0.05.

RESULTS

14 meta-analyses were included in the meta-review. Serum vitamin D and B12 levels were significantly lower in PD (SMD = -0.67 and SMD = -0.40 respectively). Homocysteine (Hcy) levels were significantly higher in PD patients (SMD = 1.26). Also the odds ratio for highest vs. lowest vitamin E intake was 0.73 which was significant. However, there was no significant difference between vitamin A, C and B6 intake or serum levels in PD vs. control groups.

CONCLUSION

Serum vitamin D and B12 levels were significantly lower in PD in comparison to healthy individuals, while Hcy level was significantly higher in PD patients. Also higher vitamin E intake was associated with significantly lower risk of development of PD in comparison to lower vitamin E intake. However, there was no significant difference between risk of PD and higher vitamin A, C and B6 intake or serum levels of folate.

Neuropathy, its Profile and Experimental Nerve Injury Neuropathic Pain Models: A Review

Neuropathy is a terrible disorder that has a wide range of etiologies. Drug-induced neuropathy, which happens whenever a chemical agent damages the peripheral nerve system, has been linked here to the iatrogenic creation of some drugs. It is potentially permanent and causes sensory impairments and paresthesia that typically affects the hands, feet, and stockings; motor participation is uncommon. It might appear suddenly or over time, and the long-term outlook varies. The wide range of chronic pain conditions experienced by people has been one of the main obstacles to developing new, more effective medications for the treatment of neuropathic pain. Animal models can be used to examine various neuropathic pain etiologies and symptoms. Several models investigate the peripheral processes of neuropathic pain, whereas some even investigate the central mechanisms, such as drug induce models like vincristine, cisplatin, bortezomib, or thalidomide, etc., and surgical models like sciatic nerve chronic constriction injury (CCI), sciatic nerve ligation through spinal nerve ligation (SNL), sciatic nerve damage caused by a laser, SNI (spared nerve injury), etc. The more popular animal models relying on peripheral nerve ligatures are explained. In contrast to chronic sciatic nerve contraction, which results in behavioral symptoms of less reliable stressful neuropathies, (SNI) spared nerve injury generates behavioral irregularities that are more feasible over a longer period. This review summarizes the latest methods models as well as clinical ideas concerning this mechanism. Every strongest current information on neuropathy is discussed, along with several popular laboratory models for causing neuropathy.

Levodopa–entacapone–carbidopa intestinal gel infusion in advanced Parkinson’s disease: real-world experience and practical guidance

As Parkinson’s disease (PD) progresses, treatment needs to be adapted to maintain symptom control. Once patients develop advanced PD, an optimised regimen of oral and transdermal medications may no longer provide adequate relief of OFF periods and motor complications can emerge. At this point, patients may wish to consider a device-aided therapy (DAT) that provides continuous dopaminergic stimulation to help overcome these issues. Levodopa–entacapone–carbidopa intestinal gel (LECIG) infusion is a recently developed DAT option. The aim of this article is twofold: (1) to give an overview of the pharmacokinetics of LECIG infusion and clinical experience to date of its use in patients with advanced PD, including real-world data and patient-reported outcomes from a cohort of patients treated in Sweden, the first country where it was introduced, and (2) based on that information to provide practical guidance for healthcare teams starting patients on LECIG infusion, whether they are transitioning from oral medications or from other DATs, including recommendations for stepwise dosing calculation and titration. In terms of clinical efficacy, LECIG infusion has been shown to have a similar effect on motor function to standard levodopa–carbidopa intestinal gel (LCIG) infusion but, due to the presence of entacapone in LECIG, the bioavailability of levodopa is increased such that lower overall levodopa doses can be given to achieve therapeutically effective plasma concentrations. From a practical standpoint, LECIG infusion is delivered using a smaller cartridge and pump system than LCIG infusion. In addition, for patients previously treated with LCIG infusion who have an existing percutaneous endoscopic transgastric jejunostomy (PEG-J) system, this is compatible with the LECIG infusion system. As it is a relatively new product, the long-term efficacy and safety of LECIG infusion remain to be established; however, real-world data will continue to be collected and analysed to provide this information and help inform future clinical decisions.

Movement disorders and neuropathies: overlaps and mimics in clinical practice

Movement disorders as well as peripheral neuropathies are extremely frequent in the general population; therefore, it is not uncommon to encounter patients with both these conditions. Often, the coexistence is coincidental, due to the high incidence of common causes of peripheral neuropathy, such as diabetes and other age-related disorders, as well as of Parkinson disease (PD), which has a typical late onset. Nonetheless, there is broad evidence that PD patients may commonly develop a sensory and/or autonomic polyneuropathy, triggered by intrinsic and/or extrinsic mechanisms. Similarly, some peripheral neuropathies may develop some movement disorders in the long run, such as tremor, and rarely dystonia and myoclonus, suggesting that central mechanisms may ensue in the pathogenesis of these diseases. Although rare, several acquired or hereditary causes may be responsible for the combination of movement and peripheral nerve disorders as a unique entity, some of which are potentially treatable, including paraneoplastic, autoimmune and nutritional aetiologies. Finally, genetic causes should be pursued in case of positive family history, young onset or multisystemic involvement, and examined for neuroacanthocytosis, spinocerebellar ataxias, mitochondrial disorders and less common causes of adult-onset cerebellar ataxias and spastic paraparesis. Deep phenotyping in terms of neurological and general examination, as well as laboratory tests, neuroimaging, neurophysiology, and next-generation genetic analysis, may guide the clinician toward the correct diagnosis and management.

Fiber selectivity of peripheral neuropathy in patients with Parkinson's disease

OBJECTIVE

To determine the function of each type of peripheral nerve fiber and investigate the possible role of levodopa (LD) in peripheral neuropathy (PN) in Parkinson's disease (PD) patients.

METHODS

We enrolled 60 patients with idiopathic PD. All PD patients were divided into three groups: levodopa exposure >3 years (LELD), levodopa exposure ≤3 years (SELD) and de novo patients with PD (NOLD). The current perception threshold (CPT), which was measured by Neurometer at 2000, 250 and 5 Hz, the level of homocysteine, Vitamin B12 and folic acid in plasma, were compared with those of sex- and age-matched healthy controls (HCs).

RESULTS

Current perception threshold was higher at 250 Hz (p < .05) and 5 Hz (p < .05) in the LELD group than the NOLD, SELD, and control group. CPT was lower at 5 Hz in the NOLD than in the HCs group (p < .05). The CPT of the more affected side of PD patients was positively correlated with H-Y stage at 5 Hz current stimulation (r = .42, p = .01). Multivariate logistic regression analysis showed that elevated homocysteine levels were the risk factor of sensory nerve injury in PD patients (p < .01). Serum homocysteine levels were positively correlated with levodopa (LD) daily dose, LD equivalent daily dose, and LD cumulative lifetime dose (p < .05).

CONCLUSIONS

Peripheral neuropathy in PD patients can occur in the early stage of PD exhibiting as hyperesthesia and is fiber selectivity, especially for Aδ and C nerve fibers. PN in PD patients is related to PD itself and long-term LD exposure. Elevated plasma homocysteine is a risk factor for PN in PD patients.

[The new Parkinson's disease pain classification system (PD-PCS)]

BACKGROUND

Chronic pain is a common non-motor symptom in patients with Parkinson's disease (PD).

AIM

To facilitate the diagnosis of pain in PD, we developed a new classification system the Parkinson's disease pain classification system (PD-PCS) and translated the corresponding validated questionnaire into German.

METHODS

A causal relationship of the respective pain syndrome with PD can be determined by four questions before assigning it hierarchically into one of three pain categories (neuropathic, nociceptive and nociplastic).

RESULTS

In the initial validation study 77% of the patients (122/159) had PD-associated pain comprising 87 (55%) with nociceptive, 36 (22%) with nociplastic and 24 (16%) with neuropathic pain. The study revealed a high validity of the questionnaire and a moderate intrarater and interrater reliability. The questionnaire has been adapted into German and employed in 30 patients.

DISCUSSION

The PD-PCS questionnaire is a valid and reliable tool to determine the relationship of a pain syndrome with PD before classifying it according to the underlying category, facilitating further diagnostics and treatment.

Peripheral neuropathy in Parkinson's disease: prevalence and functional impact on gait and balance

Peripheral neuropathy is a common problem in patients with Parkinson's disease. Peripheral neuropathy's prevalence in Parkinson's disease varies between 4.8-55%, compared with 9% in the general population. It remains unclear whether peripheral neuropathy leads to decreased motor performance in Parkinson's disease, resulting in impaired mobility and increased balance deficits. We aimed to determine the prevalence and type of peripheral neuropathy in Parkinson's disease patients and evaluate its functional impact on gait and balance. A cohort of consecutive Parkinson's disease patients assessed by movement disorders specialists based on the UK Brain Bank criteria underwent clinical, neurophysiological (nerve conduction studies and quantitative sensory testing) and neuropathological (intraepidermal nerve fibre density in skin biopsy punches) evaluation to characterize the peripheral neuropathy type and aetiology using a cross-sectional design. Gait and balance were characterized using wearable health-technology in OFF and ON medication states, and the main parameters were extracted using validated algorithms. A total of 99 Parkinson's disease participants with a mean age of 67.2 (±10) years and mean disease duration of 6.5 (±5) years were assessed. Based on a comprehensive clinical, neurophysiological and neuropathological evaluation, we found that 40.4% of Parkinson's disease patients presented peripheral neuropathy, with a predominance of small fibre neuropathy (70% of the group). In the OFF state, the presence of peripheral neuropathy was significantly associated with shorter stride length (P = 0.029), slower gait speed (P = 0.005) and smaller toe-off angles (P = 0.002) during straight walking; significantly slower speed (P = 0.019) and smaller toe-off angles (P = 0.007) were also observed during circular walking. In the ON state, the above effects remained, albeit moderately reduced. With regard to balance, significant differences between Parkinson's disease patients with and without peripheral neuropathy were observed in the OFF medication state during stance with closed eyes on a foam surface. In the ON states, these differences were no longer observable. We showed that peripheral neuropathy is common in Parkinson's disease and influences gait and balance parameters, as measured with mobile health-technology. Our study supports that peripheral neuropathy recognition and directed treatment should be pursued in order to improve gait in Parkinson's disease patients and minimize balance-related disability, targeting individualized medical care.

Parkinson's Disease Motor Subtypes Change with the Progression of the Disease: Results from the COPPADIS Cohort at 2-Year Follow-Up

BACKGROUND

Motor phenotype (MP) can be associated with a different prognosis in Parkinson's disease (PD), but it is not fixed and can change over time.

OBJECTIVE

Our aim was to analyze how the MP changed over time and to identify factors associated with the changes in PD patients from a multicenter Spanish PD cohort.

METHODS

PD patients who were recruited from January-2016 to November-2017 (baseline visit; V0) and evaluated again at a 2-year±30 days follow-up (V2) from 35 centers of Spain from the COPPADIS cohort, were included in this study.MP was calculated at both visits based on Jankovic classification in TD (tremor dominant), IND (indeterminate), or PIGD (postural instability and gait difficulty). Sociodemographic and clinical data were collected, including serum biomarkers.

RESULTS

Five hundred eleven patients (62.57±8.59 years old; 59.2%males) were included in the study. At V0, MP was: 47.4%(242/511) TD; 36.6%(187/511) PIGD; 16%(82/511) IND. Up to 38%(194/511) of the patients changed their phenotype from V0 to V2, being the most frequent from TD to IND (8.4%) and from TD to PIGD (6.7%). A worse cognitive status (OR = 0.966) and less autonomy for activities of daily living (OR  =  0.937) at V0 and a greater increase in the globalNMS burden (OR  =  1.011) from V0 to V2 were associated with changing from TD to another phenotype after 2-year follow-up.

CONCLUSION

The MP in PD can change over time. With disease progression, the percentage of cases with non-tremoric MP increases. PD patients who changed from TD to postural instability and gait difficulty increased NMS burden significantly.

Neuropathy in parkinson's disease: Risk determinants and impact on quality of life

Neuropathy has been described in significantly higher proportion of PD patients than in control subjects. This study ascertains the prevelance of neuropathy and its determinants in PD patients, in particular relation with nutritional status, along with impact of neuropathy on Quality of life.

Polyneuropathy monitoring in Parkinson's disease patients treated with levodopa/carbidopa intestinal gel

OBJECTIVES

Levodopa-carbidopa-intestinal-gel (LCIG) infusion is an effective treatment for advanced PD with motor fluctuations. Polyneuropathy occurs as a complication in 10-15% of patients. We wanted to assess the frequency of polyneuropathy in Finnish advanced Parkinson's disease (PD) patients with continuous LCIG infusion, and the value of different clinical monitoring parameters during follow-up.

MATERIALS AND METHODS

Patient records of PD patients started on LCIG infusion at Helsinki University Hospital who received nerve conduction studies at baseline and 6 months after treatment initiation were reviewed for epidemiological information, mini mental state examination, baseline and 6 months' UPRDS-III, weight, body mass index, levodopa dose (LD), plasma homocysteine levels, folate, vitamin B6 and B12.

RESULTS

Out of 19 patients (n = 6 on B-vitamin substitution), two (10.5%) developed new-onset polyneuropathy after initiation of LCIG therapy (n = 0 with vitamin substitution). Neuropathy was associated with significant weight loss (BMI reduction > 1.5), but not with other monitoring parameters. Homocysteine rose significantly in patients not substituted with B-vitamin complex, but not in patients with B-vitamin substitution. Homocysteine changes correlated with LD changes in the absence of vitamin B substitution. After oral B-vitamin substitution, both patients' polyneuropathy remained electrophysiologically and clinically stable.

CONCLUSIONS

Rates of polyneuropathy in Finnish PD patients with LCIG treatment are comparable to previous studies. Patients' weight should be included in regular follow up monitoring and can be used for patient self-monitoring. Vitamin B substitution appears to reduce coupling between levodopa dose and homocysteine and may be useful to prevent polyneuropathy related to LCIG.

Wide-field mosaics of the corneal subbasal nerve plexus in Parkinson's disease using in vivo confocal microscopy

In vivo confocal microscopy (IVCM) is a non-invasive imaging technique facilitating real-time acquisition of images from the live cornea and its layers with high resolution (1-2 µm) and high magnification (600 to 800-fold). IVCM is extensively used to examine the cornea at a cellular level, including the subbasal nerve plexus (SBNP). IVCM of the cornea has thus gained intense interest for probing ophthalmic and systemic diseases affecting peripheral nerves. One of the main drawbacks, however, is the small field of view of IVCM, preventing an overview of SBNP architecture and necessitating subjective image sampling of small areas of the SBNP for analysis. Here, we provide a high-quality dataset of the corneal SBNP reconstructed by automated mosaicking, with an average mosaic image size corresponding to 48 individual IVCM fields of view. The mosaic dataset represents a group of 42 individuals with Parkinson's disease (PD) with and without concurrent restless leg syndrome. Additionally, mosaics from a control group (n = 13) without PD are also provided, along with clinical data for all included participants.

Diagnosis and Management of Pain in Parkinson's Disease: A New Approach

Pain is a frequent and disabling non-motor feature of Parkinson's disease (PD). The recently proposed PD Pain Classification System (PD-PCS) allows for an association of pain with PD to be determined before being allocated to the main pain mechanism (i.e. nociceptive, neuropathic, and nociplastic). In this article, previous studies on treatments for pain in PD are summarized according to the pain mechanisms. A mechanistic approach to treatment is discussed. We suggest that the first step should be optimizing dopaminergic therapy before other therapy is started. When these treatments remain unsuccessful, further causes of pain must be considered. The role of drugs, invasive treatments, and physiotherapeutic interventions are discussed with a focus on older PD patients and considering polypharmacy, altered pharmacokinetics, and comorbidities.

Prevalence and Characteristics of Polyneuropathy in Atypical Parkinsonian Syndromes: An Explorative Study

(1) Background: Peripheral nerve involvement is increasingly recognized in Parkinson's disease (PD). Although non-motor symptoms and postural instability are early features of atypical parkinsonian syndromes (APS), peripheral neuropathies in APS have not been addressed in detail thus far. Therefore, the aim of this study was to investigate the prevalence and characteristics of polyneuropathies (PNP) in multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), as representative syndromes of APS. (2) Methods: In total, 8 MSA and 6 PSP patients were comprehensively analyzed regarding subjective, clinical (motor and non-motor) and paraclinical PNP features using nerve conduction studies and high resolution nerve ultrasounds (HRUS). (3) Results: A total of 87.5% of MSA and 66.7% of PSP patients complained of at least one neuropathic symptom, with electrophysiological confirmation of PNP in 50.0% of both, MSA and PSP patients. PNP symptom severity in PSP and motor nerve amplitude in MSA were associated with compromised motor function. Morphologic nerve examination by HRUS showed few alterations according to the axonal type of PNP. (4) Conclusions: The overall high PNP symptom burden may be partially credited to the significant prevalence of electrophysiologically diagnosed PNP, and impact motor aspects of APS. The findings of this exploratory study reinforce further investigations on a larger scale, in order to elucidate peripheral nerve involvement and the underlying pathophysiological mechanisms of APS.

Drug-Induced Peripheral Neuropathy: A Narrative Review

Background

Peripheral neuropathy is a painful condition deriving from many and varied etiologies. Certain medications have been implicated in the iatrogenic development of Drug Induced Peripheral Neuropathy (DIPN) and include chemotherapeutic agents, antimicrobials, cardiovascular drugs, psychotropic, anticonvulsants, among others. This review synthesizes current clinical concepts regarding the mechanism, common inciting medications, and treatment options for drug-induced peripheral neuropathy.

Methods

The authors undertook a structured search of bibliographic databases for peer-reviewed research literature using a focused review question and inclusion/exclusion criteria. The most relevant and up to date research was included.

Results

Drug-induced peripheral neuropathy is a common and painful condition caused by many different and frequently prescribed medications. Most often, DIPN is seen in chemotherapeutic agents, antimicrobials, cardiovascular drugs, psychotropic, and anticonvulsant drugs. Certain drugs exhibit more consistent neuropathic side effects, such as the chemotherapeutic compounds, but others are more commonly prescribed by a larger proportion of providers, such as the statins. DIPN is more likely to occur in patients with concomitant risk factors such as preexisting neuropathy, diabetes, and associated genetically predisposing diseases. DIPN is often difficult to treat, however medications including duloxetine, and gabapentin are shown to reduce neuropathic pain. Advanced techniques of neuromodulation offer promise though further randomized and controlled studies are needed to confirm efficacy.

Conclusion

Awareness of the drugs covered in this review and their potential for adverse neuropathic effect is important for providers caring for patients who report new onset symptoms of pain, paresthesia, or weakness. Prevention of DIPN is especially important because treatment often proves challenging. While many pharmacologic therapies have demonstrated analgesic potential in the pain caused by DIPN, many patients remain refractive to treatment. More studies are needed to elucidate the effectiveness of interventional, neuromodulating therapies.

Dietary Approaches to Improve Efficacy and Control Side Effects of Levodopa Therapy in Parkinson's Disease: A Systematic Review

Although levodopa remains the most effective drug for symptomatic management of Parkinson's Disease (PD), treatment during advanced disease stages may raise unpredictable motor fluctuations and other complications. Counteracting these complications with other pharmacological therapies may prompt a vicious circle of side effects, and here, nutritional therapy may have great potential. Knowledge about the role of diet in PD is emerging and multiple studies have investigated nutritional support specifically with respect to levodopa therapy. With this systematic review, we aim to give a comprehensive overview of dietary approaches to optimize levodopa treatment in PD. A systematic search was performed using the databases of PubMed and Scopus between January 1985 and September 2020. Nutritional interventions with the rationale to optimize levodopa therapy in human PD patients were eligible for this study and their quality was assessed with the Cochrane risk-of-bias tool. In total, we included 22 papers that addressed the effects of dietary proteins (n = 10), vitamins (n = 7), fiber (n = 2), soybeans (n = 1), caffeine (n = 1), and ketogenic diets (n = 1) on levodopa therapy. Interventions with protein redistribution diets (PRDs), dietary fiber, vitamin C, and caffeine improved levodopa absorption, thereby enhancing clinical response and reducing motor fluctuations. Furthermore, supplementation of vitamin B-12, vitamin B-6, and folic acid successfully reduced high homocysteine concentrations that emerged from levodopa metabolism and promoted many metabolic and clinical complications, such as neuropathology and osteoporosis. In conclusion, dietary interventions have the potential to optimize levodopa efficacy and control side effects. Nutrition that improves levodopa absorption, including PRDs, fiber, vitamin C, and caffeine, is specifically recommended when fluctuating clinical responses appear. Supplements of vitamin B-12, vitamin B-6, and folic acid are advised along with levodopa initiation to attenuate hyperhomocysteinemia, and importantly, their potential to treat consequent metabolic and clinical complications warrants future research.

A Novel Method for Creating a Synthetic L-DOPA Proteome and In Vitro Evidence of Incorporation

Proteinopathies are protein misfolding diseases that have an underlying factor that affects the conformation of proteoforms. A factor hypothesised to play a role in these diseases is the incorporation of non-protein amino acids into proteins, with a key example being the therapeutic drug levodopa. The presence of levodopa as a protein constituent has been explored in several studies, but it has not been examined in a global proteomic manner. This paper provides a proof-of-concept method for enzymatically creating levodopa-containing proteins using the enzyme tyrosinase and provides spectral evidence of in vitro incorporation in addition to the induction of the unfolded protein response due to levodopa.

Vitamins and Infusion of Levodopa-Carbidopa Intestinal Gel

Levodopa-carbidopa intestinal gel infusion (LCIG) is an established therapy for advanced Parkinson disease (PD), resulting in a significant improvement of quality of life. With increased LCIG adoption worldwide, potential complications due to abnormal vitamin absorption or metabolism have been reported in these patients. Neurologists are unfamiliar with vitamins physiology and pathophysiological mechanisms in case of their deficiency. Unfortunately, clinical and laboratory guidelines related to vitamin monitoring and supplementation in the context of treatment with LCIG are not available. We herein summarize the current knowledge on three vitamins that are reduced with LCIG therapy reporting on their physiology, laboratory testing, and clinical impact of their deficiency/excess. In addition, we proposed an opinion-based recommendation for clinicians treating LCIG patients. Patients and caregivers should be informed about the risk of vitamin deficiency. Vitamin B12, homocysteine, and methylmalonic acid (MMA) should be tested before starting LCIG, six months after and once/year thereafter. Vitamin B6 and folate testing is not universally available but it should be considered if homocysteine is elevated but MMA and/or total vitamin B12 are normal. Prophylaxis of vitamin deficiency should be started as soon as LCIG is implemented, possibly even before. Dietary recommendations are enough in most patients although a subgroup of patients is at higher risk and should receive Vitamin B12 regularly and cycles of B6. Finally, once diagnosed a vitamin deficiency should be readily treated and accompanied by clinical and laboratory monitoring. Resistant cases should receive non-oral routes of administration and possibly discontinue LCIG, even temporarily.

Orofacial pain in 1916 patients with early or moderate Parkinson disease

This article reports the largest epidemiological study of orofacial pain prevalence in patients with Parkinson disease to date.

Introduction:

Several studies have reported that some types of orofacial pain are more common in patients with Parkinson disease (PD) than the general population.

Objectives:

In this study, we aimed to investigate the prevalence of self-reported orofacial pain in a larger group of patients with PD than has been previously studied.

Methods:

We analysed data from 1916 participants with PD in a cross-sectional study recruited to the UK Parkinson's Pain Study who had detailed assessments of pain, motor, and nonmotor symptoms. The King's Parkinson's Pain scale was used to quantify different subtypes of pain.

Results:

A total of 139 (7.3%) patients reported the presence of some form of orofacial pain. Burning mouth syndrome was reported in 32 (1.7%), whereas chewing pain was found in 38 (2.0%) and grinding pain in 78 (4.0%). Orofacial pain was significantly more common in females (10.4%) than males (5.9%). Multiple logistic regression analysis showed a significant association between orofacial pain and pain severity, neuropathic pain, and oral motor and nonmotor dysfunction.

Conclusion:

In our study, population cohort of early patients with PD found prevalence of orofacial pain conditions similar to that in the general population.

Association between neuropathy and B-vitamins: A systematic review and meta-analysis

BACKGROUND

Peripheral neuropathy (PN) is common in patients with diseases that are in turn associated with deficiency of the B-vitamins, and vitamin treatment has shown mixed results.

METHODS

This systematic review and meta-analysis studied the association between PN/pain and B-vitamin biomarkers and investigated whether vitamin treatment can ameliorate the symptoms. PubMed and Web of Science were searched according to the study protocol.

RESULTS

A total of 46 observational and seven interventional studies were identified and included in the data synthesis. The presence of PN was associated with lowered B12 levels (pooled estimate [95% CIs] = 1.51 [1.23-1.84], n = 34, Cochran Q Test I²  = 43.3%, p = 0.003) and elevated methylmalonic acid (2.53 [1.39-4.60], n = 9, I²  = 63.8%, p = 0.005) and homocysteine (3.48 [2.01-6.04], n = 15, I²  = 70.6%, p < 0.001). B12 treatment (vs. the comparators) showed a non-significant association with symptom improvement (1.36 (0.66-2.79), n = 4, I²  = 28.9%). Treatment with B1 was associated with a significant improvement in symptoms (5.34 [1.87-15.19], n = 3, I²  = 64.6%, p = 0.059). Analysis of seven trials combined showed a non-significant higher odds ratio for improvement under treatment with the B-vitamins (2.58 [0.98-6.79], I²  = 80.0%, p < 0.001).

CONCLUSIONS

PN is associated with lowered plasma vitamin B12 and elevated methylmalonic acid and homocysteine. Overall, interventional studies have suggested that B-vitamins could improve symptoms of PN. Available trials have limitations and generally did not investigate vitamin status prior to treatment. Well-designed studies, especially in non-diabetes PN, are needed. This meta-analysis is registered at PROSPERO (ID: CRD42020144917).

Comprehensive assessment of levodopa-carbidopa intestinal gel for Turkish advanced Parkinson’s disease patients

Background/aim

Levodopa-carbidopa intestinal gel (LCIG) is an effective treatment modality in the management of advanced Parkinson’s disease (PD) despite frequent adverse events and different rates of dropouts. Efficacy and safety data regarding Turkish patients on LCIG are limited. This study aims to report in detail the efficacy and adverse effect profile of LCIG among advanced PD patients from a Turkish center for movement disorders.

Materials and methods

Twenty-two patients (50% male) who started receiving LCIG between December 2014 and March 2020 were recruited. The efficacy of LCIG was assessed with the Unified Parkinson’s Disease Rating Scale (UPDRS III), Clinical Global İmprovement (CGI) scale, and Quality of Life scale (PDQ8). Improvements in gait disorders and nonmotor features were also questioned. Adverse events (AE) were collated into 3 topics: related to percutaneous endoscopic gastrojejunostomy (PEG-J), device-related, and LCIG infusion-related.

Results

Mean age and pre-LCIG disease duration were 66.7 (8.8) and 13.3 (8.0) years respectively. UPDRS III scores and H-Y scale assessments significantly improved. Better quality of life scores, clinical global improvements, and improvements in dysarthria, dysphagia, and gait were observed. None of our patients dropped out or died during a mean 17.5-month (12.3) period. Overall 20 (90.9%) patients experienced at least one AE. Twelve patients had PEG-J–related complications; three had acute abdomen. Eight (36.4%) patients had device-associated problems. Half of the patients required at least one additional endoscopic procedure and 7 had a device replaced. Mean body weight decreased from 69.5 to 62.5 kg and seven patients had newly onset PNP at a follow-up electromyography. Dyskinesia related to LCIG infusion was observed in 5 (22.7%) patients. There was no significant increase in hallucination among patients.

Conclusion

LCIG is an efficient treatment modality in the management of Turkish patients with advanced Parkinson’s disease. Although most of the patients had at least one AE, none of them dropped out. Patient selection, patient compliance, and collaborative management are important steps affecting the success of modality.

Peripheral synucleinopathy in Parkinson disease with LRRK2 G2385R variants

Objective

Recent studies demonstrated cutaneous phosphorylated α synuclein (p‐syn) deposition in idiopathic and some monogenetic Parkinson disease (PD) patients, suggesting synucleinopathy identical to that in the brain. Although the LRRK2 Gly2385Arg (G2385R) variant is a common PD risk factor in the Chinese population, the pathogenesis of PD with G2385R variant has not been reported. We investigated whether synucleinopathy and small fiber neuropathy (SFN) are associated with the G2385R variant.

Methods

We performed genotyping in 59 PD patients and 30 healthy controls from the skin biopsy database. The scale of SFN was assessed, as well as bright‐field immunohistochemistry against antiprotein gene product 9.5 (PGP9.5) and double‐labeling immunofluorescence with anti‐PGP9.5 and anti‐p‐syn.

Results

(1) p‐syn deposited in the skin nerve fibers of G2385R carrier PD patients, which was a different pattern from noncarriers, without no difference observed between proximal and distal regions; (2) decreased distal intraepidermal nerve fiber density was found in both the G2385R carrier and the noncarrier PD group, and was negatively correlated with composite autonomic symptom score‐31 item (COMPASS‐31) scores; (3) PD patients with the G2385R variant showed a more peculiar clinical profile than noncarriers with a higher nonmotor symptoms scale, COMPASS‐31 score, and levodopa equivalent dose, in addition to an increased prevalence of certain autonomic symptoms or rapid eye movement sleep behavior disorders.

Interpretation

Synucleinopathy is related to the LRRK2 G2385R genotype and implies a different pathogenesis in G2385R variant carriers and noncarriers. This study also extended the clinical profiles of PD patients with the G2385R variant.

Parkinson's disease with restless legs syndrome-an in vivo corneal confocal microscopy study

Small fiber neuropathy (SFN) has been suggested as a trigger of restless legs syndrome (RLS). An increased prevalence of peripheral neuropathy has been demonstrated in Parkinson's disease (PD). We aimed to investigate, in a cross-sectional manner, whether SFN is overrepresented in PD patients with concurrent RLS relative to PD patients without RLS, using in vivo corneal confocal microscopy (IVCCM) and quantitative sensory testing (QST) as part of small fiber assessment. Study participants comprised of age- and sex-matched PD patients with (n = 21) and without RLS (n = 21), and controls (n = 13). Diagnosis of RLS was consolidated with the sensory suggested immobilization test. Assessments included nerve conduction studies (NCS), Utah Early Neuropathy Scale (UENS), QST, and IVCCM, with automated determination of corneal nerve fiber length (CNFL) and branch density (CNBD) from wide-area mosaics of the subbasal nerve plexus. Plasma neurofilament light (p-NfL) was determined as a measure of axonal degeneration. No significant differences were found between groups when comparing CNFL (p = 0.81), CNBD (p = 0.92), NCS (p = 0.82), and QST (minimum p = 0.54). UENS scores, however, differed significantly (p = 0.001), with post-hoc pairwise testing revealing higher scores in both PD groups relative to controls (p = 0.018 and p = 0.001). Analysis of all PD patients (n = 42) revealed a correlation between the duration of L-dopa therapy and CNBD (ρ = -0.36, p = 0.022), and p-NfL correlated with UENS (ρ = 0.35, p = 0.026) and NCS (ρ = -0.51, p = 0.001). Small and large fiber neuropathy do not appear to be associated with RLS in PD. Whether peripheral small and/or large fiber pathology associates with central neurodegeneration in PD merits further longitudinal studies.

Wearable Health Technology to Quantify the Functional Impact of Peripheral Neuropathy on Mobility in Parkinson's Disease: A Systematic Review

The occurrence of peripheral neuropathy (PNP) is often observed in Parkinson’s disease (PD) patients with a prevalence up to 55%, leading to more prominent functional deficits. Motor assessment with mobile health technologies allows high sensitivity and accuracy and is widely adopted in PD, but scarcely used for PNP assessments. This review provides a comprehensive overview of the methodologies and the most relevant features to investigate PNP and PD motor deficits with wearables. Because of the lack of studies investigating motor impairments in this specific subset of PNP-PD patients, Pubmed, Scopus, and Web of Science electronic databases were used to summarize the state of the art on PNP motor assessment with wearable technology and compare it with the existing evidence on PD. A total of 24 papers on PNP and 13 on PD were selected for data extraction: The main characteristics were described, highlighting major findings, clinical applications, and the most relevant features. The information from both groups (PNP and PD) was merged for defining future directions for the assessment of PNP-PD patients with wearable technology. We established suggestions on the assessment protocol aiming at accurate patient monitoring, targeting personalized treatments and strategies to prevent falls and to investigate PD and PNP motor characteristics.

Changes of Peripheral Nerve Function and Vitamin B12 Level in People With Parkinson's Disease

Background and Purpose: Peripheral nerve function plays an important role in balance control. Impairment of peripheral sensory information appears in people with Parkinson's disease (PD). Furthermore, there is a link between peripheral nerve disorders and vitamin B₁₂ level. Here, we studied whether there were deficits of peripheral nerve function and vitamin B₁₂ level, which may lead to decreased postural stability in PD.

Methods: Fifty PD and 50 age-matched healthy subjects were enrolled in the study. This study evaluated folic acid and vitamin B₁₂ levels in serum. Postural balance was studied according to the clinical Tinetti scale. Some comprehensive physiological assessments of peripheral nerve functions, including peripheral sensation, the perception of temperature, pain, and touch sensations, were also undertaken in this study.

Results: Compared with the control group, vitamin B₁₂ and folic acid were decreased in PD (P < 0.05). Furthermore, the PD group exhibited declines in peripheral nerve functions, including touch, temperature, pain, and nerve conduction velocity (P < 0.05). Statistical tests identified a significant association between decreased peripheral nerve function and poor balance according to the Tinetti scale (P < 0.05). Low vitamin B₁₂ levels were also associated with deficits of peripheral nerve function, cumulative levodopa dose, and poor balance in PD (P < 0.05).

Conclusions: Data suggested that peripheral nerve function was impaired in people with PD. Deficits of sensory input and low vitamin B₁₂ level may contribute to balance deficits in PD.

Correlates of polyneuropathy in Parkinson's disease

Objective

Previous studies in Parkinson’s disease (PD) patients have demonstrated a high prevalence of polyneuropathy (PNP) and pronounced alpha‐Synuclein pathology in dermal nerve fibers already at early disease stages. The aim of this study was to analyze associations between the prevalence and severity of PNP with nonmotor and motor symptoms in PD patients.

Methods

Fifty PD patients were characterized comprehensively for the presence of clinical symptoms (nonmotor and motor), electrophysiologic alterations and – for the first time – using high‐resolution ultrasound of peripheral nerves.

Results

Sixty‐two percent of PD patients showed electrophysiological pathology of PNP. The prevalence of patient‐reported PNP symptoms was 86% and was particularly present in patients with longer disease duration, compromised scores of nonmotor and motor symptoms as well as with a negative evaluation of quality of life. Seventy‐five percent of patients showed morphologic alterations similar to axonal PNP in high‐resolution ultrasound compared to healthy controls.

Interpretation

The study demonstrates the high burden of peripheral nervous system disease in Parkinson's disease. It advocates further studies to delineate the underlying pathophysiological mechanisms in order to optimize treatment approaches for PD, including the associated PNP.

Small Fibre Neuropathy in Parkinson's Disease: Comparison of Skin Biopsies from the More Affected and Less Affected Sides

We assessed small nerve fibre degeneration and regeneration in more and less affected sides in Parkinson’s disease (PD). Bilateral skin biopsies from 23 PD patients were immunostained for PGP9.5 for Intraepidermal Nerve Fibre Density (IENFD) and GAP-43 for mean axonal length (MAL), total epidermal (TNFL) and subepidermal nerve fibre length (SKTNFL). IENFD (p < 0.001) and SKTNFL (p < 0.001) were lower, whilst MAL (p < 0.001) and TNFL (p < 0.05) were higher in more affected versus less affected side. These results suggest increased small nerve fibre degeneration accompanied by enhanced nerve regeneration on the side more affected by PD and GAP-43 usefulness in skin biopsy assessment.

Potential use of corneal confocal microscopy in the diagnosis of Parkinson's disease associated neuropathy

Parkinson’s disease (PD) is a chronic, progressive neurodegenerative disease affecting about 2–3% of population above the age of 65. In recent years, Parkinson’s research has mainly focused on motor and non-motor symptoms while there are limited studies on neurodegeneration which is associated with balance problems and increased incidence of falls. Corneal confocal microscopy (CCM) is a real-time, non-invasive, in vivo ophthalmic imaging technique for quantifying nerve damage in peripheral neuropathies and central neurodegenerative disorders. CCM has shown significantly lower corneal nerve fiber density (CNFD) in patients with PD compared to healthy controls. Reduced CNFD is associated with decreased intraepidermal nerve fiber density in PD. This review provides an overview of the ability of CCM to detect nerve damage associated with PD.

Is sudoscan a reliable tool in detecting small fiber neuropathy in Parkinson's disease patients?

Aim: Previous studies have revealed uncertainties concerning the utility of sudoscan in identifying small fiber neuropathy in Parkinson's disease (PD). Patients & methods: We searched for a significant reduction of electrochemical skin conductance (ESC) in 67 PD patients versus 66 controls with similar characteristics. We conducted analysis of the subgroups of PD patients without diabetes using sudoscan technology. Results: There is no discrimination between patients and controls relative to feet ESC, the modified Hoehn and Yahr Scale and/or Unified Parkinson's Disease Rating Scale. ESC in patients did not differ significantly according to the Unified Parkinson's Disease Rating Scale score. The oldest PD patients with cardiovascular risk factors have more marked small fibers dysfunction. Conclusion: The sudoscan procedure did not show advantage in the diagnosis of small fiber neuropathy. Its diagnostic value increases in some subgroups of patients with cardiovascular co-morbidity.

Serum B12, Homocysteine Levels, and their Effect on Peripheral Neuropathy in Parkinson's Disease: Indian Cohort

Background:

Cobalamin deficiency, either due to dietary inadequacy or increased consumption attributable to levodopa-mediated metabolic disturbance, and resultant hyperhomocysteinemia may contribute to peripheral neuropathy (PN) in Parkinson's disease (PD).

Aim:

The aim of the study is to assess the prevalence of Vitamin B12 deficiency, hyperhomocysteinemia in Indian PD patients, and their association with PN.

Materials and Methods:

Clinical details were collected in 93 patients over a period of 2 years. Seventy controls were included in the study. Serum B12, homocysteine, folate, electroneurography, and autonomic function tests were done. The prevalence of B12 deficiency and hyperhomocysteinemia in PD patients and controls was assessed. The association of B12 and homocysteine levels with patients’ age, disease duration, levodopa equivalent daily dose, cumulative levodopa dose, Unified Parkinson's Disease Rating Scale-III off score, modified Hoehn and Yahr score, and presence or absence of PN was studied.

Results:

Serum B12, homocysteine levels, prevalence of B12 deficiency, and hyperhomocysteinemia were no different between cases and controls. Seven of 93 (9.68%) PD patients had PN. The median values of serum B12, folate, and homocysteine levels across patients with or without PN could not be compared as only seven of our patients had PN.

Conclusion:

The prevalence of B12 deficiency, hyperhomocysteinemia, and incidence of PN among our patients is very less when compared to the Western population. The conjecture that PN in PD patients may be secondary to B12 deficiency/hyperhomocysteinemia stands as a speculation.

Nutritional neuropathies

Neuropathies associated with nutritional deficiencies are routinely encountered by the practicing neurologist. Although these neuropathies assume different patterns, most are length-dependent, sensory axonopathies. Cobalamin deficiency neuropathy is the exception, often presenting with a non-length-dependent sensory neuropathy. Patients with cobalamin and copper deficiency neuropathy characteristically have concomitant myelopathy, whereas vitamin E deficiency is uniquely associated with a spinocerebellar syndrome. In contrast to those nutrients for which deficiencies produce neuropathies, pyridoxine toxicity results in a non-length-dependent sensory neuronopathy. Deficiencies occur in the context of malnutrition, malabsorption, increased nutrient loss (such as with dialysis), autoimmune conditions such as pernicious anemia, and with certain drugs that inhibit nutrient absorption. When promptly identified, therapeutic nutrient supplementation may result in stabilization or improvement of these neuropathies.

Increased Prevalence of Polyneuropathy in Parkinson's Disease Patients: An Observational Study

BACKGROUND

The independent contribution of levodopa exposure and Parkinson's disease (PD) to the risk of polyneuropathy is not established.

OBJECTIVE

This study investigated whether patients with newly diagnosed PD without previous exposure to antiparkinsonian drugs have higher prevalence of polyneuropathy than the general population.

METHODS

Using the UK General Practice Research Database, presence of polyneuropathy in the previous 3 years was assessed.

RESULTS

Of 5089 PD patients and 19,897 controls, polyneuropathy was confirmed in 15 PD patients (0.29% ) and 24 controls (0.12% ). Polyneuropathy prevalence was 2.4-fold higher in PD patients than controls.

CONCLUSIONS

In this observational study, PD patients had a higher prevalence of preexisting polyneuropathy that cannot be explained by adverse effects of antiparkinsonian drugs.

Large-Fiber Neuropathy in Parkinson's Disease: Clinical, Biological, and Electroneurographic Assessment of a Romanian Cohort

(1) Background: Increased attention has lately been given to polyneuropathy in Parkinson’s Disease (PD). Several papers postulated that large-fiber neuropathy (PNP) in PD is related to vitamin B12 deficiency and L-Dopa exposure. (2) Methods: Using a cross-sectional, observational study, we evaluated 73 PD patients without a previously known cause of PNP using clinical scores (UPDRS II and III and Toronto Clinical Scoring System), biological evaluation of vitamin B12 and folic acid, and nerve conduction studies to assess the prevalence and features of PNP. (3) Results: The prevalence of PNP was 49.3% in the study group. In the L-Dopa group, the frequency of PNP was 67.3% as compared to PNP in the non-L-Dopa group, where one subject had PNP (χ² = 23.41, p < 0.01). PNP was predominantly sensory with mild to moderate axonal loss. Cyanocobalamin correlated with L-Dopa daily dose (r = −0.287, p < 0.05) and L-Dopa duration of administration (r = −0.316, p < 0.05). L-Dopa daily dose correlated with the amplitudes of sensory nerve action potentials of the superficial peroneal and radial nerves (r = −0.312, p < 0.05) (r = −0.336, p < 0.05), respectively. (4) Conclusions: PNP is more frequent in L-Dopa-treated patients than in L-Dopa-naïve patients. The results imply that longer exposure to high doses of L-Dopa may cause vitamin B12 and folate imbalance and PNP, secondarily.