Hyperalgesia and laser evoked potentials alterations in hemiparkinson: Evidence for an abnormal nociceptive processing

Periaqueductal grey and spinal cord pathology contribute to pain in Parkinson's disease

Pain is a key non-motor feature of Parkinson's disease (PD) that significantly impacts on life quality. The mechanisms underlying chronic pain in PD are poorly understood, hence the lack of effective treatments. Using the 6-hydroxydopamine (6-OHDA) lesioned rat model of PD, we identified reductions in dopaminergic neurons in the periaqueductal grey (PAG) and Met-enkephalin in the dorsal horn of the spinal cord that were validated in human PD tissue samples. Pharmacological activation of D₁-like receptors in the PAG, identified as the DRD5⁺ phenotype located on glutamatergic neurons, alleviated the mechanical hypersensitivity seen in the Parkinsonian model. Downstream activity in serotonergic neurons in the Raphé magnus (RMg) was also reduced in 6-OHDA lesioned rats, as detected by diminished c-FOS positivity. Furthermore, we identified increased pre-aggregate α-synuclein, coupled with elevated activated microglia in the dorsal horn of the spinal cord in those people that experienced PD-related pain in life. Our findings have outlined pathological pathways involved in the manifestation of pain in PD that may present targets for improved analgesia in people with PD.

Pain in Parkinson's disease and the role of the subthalamic nucleus

Pain is a frequent and poorly treated symptom of Parkinson's disease, mainly due to scarce knowledge of its basic mechanisms. In Parkinson's disease, deep brain stimulation of the subthalamic nucleus is a successful treatment of motor symptoms, but also might be effective in treating pain. However, it has been unclear which type of pain may benefit and how neurostimulation of the subthalamic nucleus might interfere with pain processing in Parkinson's disease. We hypothesized that the subthalamic nucleus may be an effective access point for modulation of neural systems subserving pain perception and processing in Parkinson's disease. To explore this, we discuss data from human neurophysiological and psychophysical investigations. We review studies demonstrating the clinical efficacy of deep brain stimulation of the subthalamic nucleus for pain relief in Parkinson's disease. Finally, we present some of the key insights from investigations in animal models, healthy humans and Parkinson's disease patients into the aberrant neurobiology of pain processing and consider their implications for the pain-relieving effects of subthalamic nucleus neuromodulation. The evidence from clinical and experimental studies supports the hypothesis that altered central processing is critical for pain generation in Parkinson's disease and that the subthalamic nucleus is a key structure in pain perception and modulation. Future preclinical and clinical research should consider the subthalamic nucleus as an entry point to modulate different types of pain, not only in Parkinson's disease but also in other neurological conditions associated with abnormal pain processing.

Towards optimising experimental quantification of persistent pain in Parkinson's disease using psychophysical testing

People with Parkinson's disease (PD) may live for multiple decades after diagnosis. Ensuring that effective healthcare provision is received across the range of symptoms experienced is vital to the individual's wellbeing and quality of life. As well as the hallmark motor symptoms, PD patients may also suffer from non-motor symptoms including persistent pain. This type of pain (lasting more than 3 months) is inconsistently described and poorly understood, resulting in limited treatment options. Evidence-based pain remedies are coming to the fore but therapeutic strategies that offer an improved analgesic profile remain an unmet clinical need. Since the ability to establish a link between the neurodegenerative changes that underlie PD and those that underlie maladaptive pain processing leading to persistent pain could illuminate mechanisms or risk factors of disease initiation, progression and maintenance, we evaluated the latest research literature seeking to identify causal factors underlying persistent pain in PD through experimental quantification. The majority of previous studies aimed to identify neurobiological alterations that could provide a biomarker for pain/pain phenotype, in PD cohorts. However heterogeneity of patient cohorts, result outcomes and methodology between human psychophysics studies overwhelmingly leads to inconclusive and equivocal evidence. Here we discuss refinement of pain-PD paradigms in order that future studies may enhance confidence in the validity of observed effect sizes while also aiding comparability through standardisation. Encouragingly, as the field moves towards cross-study comparison of data in order to more reliably reveal mechanisms underlying dysfunctional pain processing, the potential for better-targeted treatment and management is high.

Effects of safinamide on pain in Parkinson's disease with motor fluctuations: an exploratory study

Pain is a common and disabling non-motor symptom (NMS) of Parkinson's disease (PD), which occurs through the course of the disease, often unrecognized and undertreated. For this study, we evaluated the efficacy and safety of safinamide to reduce pain in PD patients with motor fluctuations. A total of 13 PD patients with pain receiving safinamide (Xadago®, 100 mg/daily) were prospectively evaluated for 12 weeks. The primary outcome measures were changes in the total score of the King's Pain Scale for Parkinson's Disease (KPPS), Brief Pain Inventory (BPI) Intensity and Interference, and the Numeric Rating Scale (NRS). Secondary outcomes were the proportion of pain responders, changes in the Clinical Global Impression of Change (CGI), the Parkinson's disease Quality of Life 39 (PDQ39), the Unified Parkinson's Disease Rating Scale parts III and IV (UPDRS III and IV), and laser-evoked potentials (LEPs). LEPs were used to assess potential changes in the central processing of nociceptive inputs. The safety profile was evaluated based on the occurrence of treatment-emergent side effects and the dropout rate. After 12 weeks of add-on safinamide therapy, a significant improvement was noted in the primary (KPPS, BPI Intensity and interference, and NRS) and the secondary outcomes (UPDRS III, IV, CGI, and PDQ39). No significant changes in LEP complexes were observed. All patients completed the study and no treatment-emergent side effects were reported. Our preliminary findings suggest that safinamide 100 mg/day may be effective for the management of pain in PD patients with motor fluctuations and is safe. Further randomized controlled trials are needed to confirm its efficacy.

Potential of animal models for advancing the understanding and treatment of pain in Parkinson's disease

Pain is a commonly occurring non-motor symptom of Parkinson’s disease (PD). Treatment of pain in PD remains less than optimal and a better understanding of the underlying mechanisms would facilitate discovery of improved analgesics. Animal models of PD have already proven helpful for furthering the understanding and treatment of motor symptoms of PD, but could these models offer insight into pain in PD? This review addresses the current position regarding pain in preclinical models of PD, covering the face and predictive validity of existing models and their use so far in advancing understanding of the mechanisms contributing to pain in PD. While pain itself is not usually measured in animals, nociception in the form of thermal, mechanical or chemical nociceptive thresholds offers a useful readout, given reduced nociceptive thresholds are commonly seen in PD patients. Animal models of PD including the reserpine-treated rat and neurodegenerative models such as the MPTP-treated mouse and 6-hydroxydopamine (6-OHDA)-treated rat each exhibit reduced nociceptive thresholds, supporting face validity of these models. Furthermore, some interventions known clinically to relieve pain in PD, such as dopaminergic therapies and deep brain stimulation of the subthalamic nucleus, restore nociceptive thresholds in one or more models, supporting their predictive validity. Mechanistic insight gained already includes involvement of central and spinal dopamine and opioid systems. Moving forward, these preclinical models should advance understanding of the cellular and molecular mechanisms underlying pain in PD and provide test beds for examining the efficacy of novel analgesics to better treat this debilitating non-motor symptom.

An overview of pain in Parkinson's disease

Pain is a common non-motor symptom of Parkinson's disease (PD) and the prevalence of pain among PD patients varies because of the disease stage, co-morbidities, and evaluating tools. Risk factors for pain in PD include an early age of onset, long disease duration, motor complications, concomitant depressive symptoms, female gender, and associated medical conditions. In patients with PD, pain can be classified as musculoskeletal pain, chronic body pain (central or visceral), fluctuation-related pain, nocturnal pain, orofacial pain, pain with discolouration/oedema/swelling, and radicular/neuropathic pain; musculoskeletal pain as the most common type. Potential underlying mechanisms include a disruption of peripheral nociception and alterations in central pain threshold/processing. Genetic polymorphisms in genes that confer pain susceptibility might also play a role in the occurrence of pain in PD. In advanced stage of patients with PD, polyneuropathy could occur in patients using high dosage of levodopa. Pain often correlates to other non-motor symptoms of PD, including depression, sleep, and autonomic symptoms. Dopaminergic drugs, non-dopaminergic medications, botulinum toxin, deep brain stimulation, and physiotherapy have shown some benefits for certain types of PD-related pain. An increased awareness of pain as a common non-motor symptom of PD provides further insights into sensory system dysregulation in this disease. In this review, we aim to summarizes the clinical features of pain in patients with PD and emphasize the latest evidence of pain related to levodopa treatment.

Conditioned pain modulation in drug-naïve patients with de novo Parkinson's disease

Background

Pain is highly prevalent in patients with Parkinson’s disease (PD), but underlying pathophysiological mechanisms are largely unclear. In many chronic pain syndromes deficits in endogenous pain inhibition have been detected that can be assessed using conditioned pain modulation paradigms. Previous studies employing this approach in medicated PD patients did not find abnormal pain inhibition. However, these results might have been confounded by residual dopaminergic medication.

Methods

An established conditioned pain modulation paradigm was used in 17 drug-naïve de novo PD patients and 17 healthy age and gender-matched controls. We tested i) whether conditioned pain modulation responses differed between the patient and control group and ii) whether pain inhibition differed between PD subtypes.

Results

PD patients and healthy controls did not differ in their conditioned pain modulation responses. Furthermore, there were no significant differences in CPM responses depending on the PD subtype. However, at a descriptive level, tremor-dominant patients showed a tendency for better descending pain inhibition compared to akinetic-rigid and mixed type patients.

Conclusions

In this first study investigating conditioned pain modulation in de novo PD patients, we found no additional impairment in descending pain modulation besides the known age-related decline. Our findings indicate that mechanisms other than an impaired descending inhibition contribute to high pain prevalence rates in PD and suggest that mechanisms underlying pain may differ between PD subtypes.

Electronic supplementary material

The online version of this article (10.1186/s42466-019-0029-x) contains supplementary material, which is available to authorized users.

Parkinson disease: A systemic review of pain sensitivities and its association with clinical pain and response to dopaminergic stimulation

Patients with Parkinson disease (PD) experience hyperalgesia on evoked pain sensitivity testing, although the relationship of this with persistent pain in PD is less certain. Studies examining this have generated contradictory findings. Further, the role of dopaminergic deficiency as an underlying substrate for hyperalgesia is controversial. We report the results of meta-analyses of the PD pain sensitivity literature in an attempt to answer these questions. We identified 429 records, of which ten articles compared pain sensitivity between PD patients that experienced clinical pain (PDP) to those who did not (PDNP), and twenty studies that examined the effect of dopaminergic medications on pain sensitivity in PD patients. PDP patients experienced a moderate increase in pain sensitivity, had more severe disease, required higher dosages of medication, and were more likely to be female when compared to those PDNP patients. PD patients also had reduced pain sensitivity when tested on dopaminergic medications compared to when they were not on medications. Overall, the results of this systematic review and meta-analysis supports the hypothesis that hyperalgesia contributes to clinical pain in PD, and that the underlying mechanism may be dopaminergically driven.

Pain sensitivity in Parkinson's disease: Systematic review and meta-analysis

INTRODUCTION

Pain is a common and disabling non-motor symptom of Idiopathic Parkinson's disease (PD) but its underlying pathophysiological mechanisms are not well understood. There is evidence to suggest that altered pain sensitivity may contribute to the experience of pain in PD patients, but clinical studies investigating this have yielded inconsistent results.

OBJECTIVES

To examine whether pain thresholds are altered in PD patients compared to normal healthy controls (HC), via the use of systematic review and meta-analysis.

DATA SOURCES

A systematic search of the MEDLINE and EMBASE library from 1966 to April 2015.

STUDY SELECTION

Studies that compared pain thresholds in PD patients versus HC were included in the systematic review. Additionally, data comparing PD patients off dopaminergic medications (PD_Moff) to HC off medications (HC_Moff) were pooled for meta-analysis by pain modality.

MAIN OUTCOMES

Heat pain threshold, cold pain threshold, electrical pain threshold, nociceptive withdrawal reflex threshold, pressure pain threshold, and pain ratings.

RESULTS

22 studies were reviewed, comprising of 616 PD and 451 HC. In the comparison of PD_Moff versus HC_Moff, a large majority of trials (15/19) found reduced pain thresholds (increased pain sensitivity) in PD patients. Meta-analysis of these trials revealed significantly reduced pain thresholds, of moderate to large effect size, in PD patients across all pain modalities. Results were much more heterogenous when PD patients on medications were compared with HC off medications, with most trials reporting no significant difference in pain thresholds between groups. No significant differences were found in pain thresholds for trials that compared PD patients on medications and HC on medications.

CONCLUSION

PD patients are more sensitive to noxious stimuli compared to HC when tested in the off medication state. This increase in pain sensitivity is observed across all modalities, but is not as apparent when PD patients are administered Levodopa, suggesting that dopamine deficient states may contribute to hyperalgesia. However, it remains to be seen whether or not increased pain sensitivity translates clinically into increased prevalence of pain. Similarly, it is unclear if dopaminergic medications influence pain sensitivity. Performing a meta-analysis on studies comparing pain thresholds in PD patients with and without pain, and on and off dopaminergic medications, may draw more definitive conclusions in this regard.

Pharmacological therapies for pain in Parkinson's disease - a review paper

INTRODUCTION

Parkinson's disease (PD) is a neurodegenerative movement disorder characterized by the loss of dopamine containing cells in the substantia nigra, with pain being one of the most common, yet frequently misunderstood symptoms. The prevalence of pain in PD populations ranges from 40-85% and is usually categorized under the following types: i) musculoskeletal pain ii) radicular and neuropathic pain iii) dystonia-related pain iv) akathitic pain and iv) central parkinsonian pain. Areas covered: The aim of this literature review was to document and present the common and uncommon pharmaceutical therapies that treat and/or alleviate these types of pain in PD. The PubMed database was searched with keywords: "Parkinson's disease", "Pain", and "Pharmacological Therapies". Research articles involving randomized, controlled trials were included as well as case studies and qualitative studies. Expert commentary: Given the increased prevalence of pain in PD populations, there is a need for a clear understanding of the types of pain treatments available and how they can be best combined to fit the specific needs of each patient.

Understanding and Treating Pain Syndromes in Parkinson's Disease

Pain affects many people with Parkinson's disease (PD) and diminishes their quality of life. Different types of pain have been described, but their related pathophysiological mechanisms remain unclear. The aim of this chapter is to provide movement disorders specialists an update about the pathophysiology of pain and a practical guide for the management of pain syndromes in clinical practice. This chapter reviews current knowledge on the pathophysiological mechanisms of sensory changes and pain in PD, as well as assessment and treatment procedures to manage these symptoms. In summary, changes in peripheral and central pain processing have been demonstrated in PD patients. A decrease in pain threshold and tolerance to several stimuli, a reduced nociceptive withdrawal reflex, a reduced pain threshold, and abnormal pain-induced activation in cortical pain-related areas have been reported. There is no direct association between improvement of motor symptoms and sensory/pain changes, suggesting that motor and nonmotor symptoms do not inevitably share the same mechanisms. Special care in pain assessment in PD is warranted by the specific pathophysiological aspects and the complexity of motor and nonmotor symptoms associated with pain symptoms. Rehabilitation may represent a valid option to manage pain syndromes in PD. However, further research in this field is needed. An integrated approach to pain involving a multidisciplinary team of medical specialists and rehabilitation experts should allow a comprehensive approach to pain in PD.

Pathophysiology of Motor Dysfunction in Parkinson's Disease as the Rationale for Drug Treatment and Rehabilitation

Cardinal motor features of Parkinson's disease (PD) include bradykinesia, rest tremor, and rigidity, which appear in the early stages of the disease and largely depend on dopaminergic nigrostriatal denervation. Intermediate and advanced PD stages are characterized by motor fluctuations and dyskinesia, which depend on complex mechanisms secondary to severe nigrostriatal loss and to the problems related to oral levodopa absorption, and motor and nonmotor symptoms and signs that are secondary to marked dopaminergic loss and multisystem neurodegeneration with damage to nondopaminergic pathways. Nondopaminergic dysfunction results in motor problems, including posture, balance and gait disturbances, and fatigue, and nonmotor problems, encompassing depression, apathy, cognitive impairment, sleep disturbances, pain, and autonomic dysfunction. There are a number of symptomatic drugs for PD motor signs, but the pharmacological resources for nonmotor signs and symptoms are limited, and rehabilitation may contribute to their treatment. The present review will focus on classical notions and recent insights into the neuropathology, neuropharmacology, and neurophysiology of motor dysfunction of PD. These pieces of information represent the basis for the pharmacological, neurosurgical, and rehabilitative approaches to PD.

Pain in Neurodegenerative Disease: Current Knowledge and Future Perspectives

Neurodegenerative diseases are going to increase as the life expectancy is getting longer. The management of neurodegenerative diseases such as Alzheimer's disease (AD) and other dementias, Parkinson's disease (PD) and PD related disorders, motor neuron diseases (MND), Huntington's disease (HD), spinocerebellar ataxia (SCA), and spinal muscular atrophy (SMA), is mainly addressed to motor and cognitive impairment, with special care to vital functions as breathing and feeding. Many of these patients complain of painful symptoms though their origin is variable, and their presence is frequently not considered in the treatment guidelines, leaving their management to the decision of the clinicians alone. However, studies focusing on pain frequency in such disorders suggest a high prevalence of pain in selected populations from 38 to 75% in AD, 40% to 86% in PD, and 19 to 85% in MND. The methods of pain assessment vary between studies so the type of pain has been rarely reported. However, a prevalent nonneuropathic origin of pain emerged for MND and PD. In AD, no data on pain features are available. No controlled therapeutic trials and guidelines are currently available. Given the relevance of pain in neurodegenerative disorders, the comprehensive understanding of mechanisms and predisposing factors, the application and validation of specific scales, and new specific therapeutic trials are needed.

Contact Heat Evoked Potentials (CHEPs) in Patients with Mild-Moderate Alzheimer's Disease and Matched Control--A Pilot Study

OBJECTIVE

Clinical studies have found that patients with Alzheimer's disease report pain of less intensity and with a lower affective response, which has been thought to be due to altered pain processing. The authors wished to examine the cerebral processing of non-painful and painful stimuli using somatosensory evoked potentials and contact heat evoked potentials in patients with Alzheimer's disease and in healthy elderly controls.

DESIGN

Case-control study

SETTING AND SUBJECTS

Twenty outpatients with mild-moderate Alzheimer's disease and in 17 age- and gender-matched healthy controls were included

METHOD

Contact heat evoked potentials and somatosensory evoked potentials were recorded in all subjects. Furthermore, warmth detection threshold and heat pain threshold were assessed. Patients and controls also rated quality and intensity of the stimuli.

RESULTS

The authors found no difference on contact heat evoked potential amplitude (P = 0.59) or latency of N2 or P2 wave (P = 0.62 and P = 0.75, respectively) between patients and controls. In addition, there was no difference in regard to pain intensity scores or pain quality. The patients and controls had similar warmth detection threshold and heat pain threshold. Somatosensory evoked potentials, amplitude, and latency were within normal range and similar for the two groups.

CONCLUSIONS

The findings suggest that the processing of non-painful and painful stimuli is preserved in patients with mild to moderate Alzheimer's disease.

Facilitated temporal summation of pain at spinal level in Parkinson's disease

BACKGROUND

Pain is one of the major nonmotor symptoms of Parkinson's disease. We hypothesized that Parkinson's disease patients could show an early diffuse abnormal processing of the nociceptive inputs also in the absence of clinical pain syndrome and that this could represent the physiopathological substrate to explain the high incidence of diffuse pain symptoms.

MATERIALS AND METHODS

We used the temporal summation threshold of the nociceptive withdrawal reflex and the related pain sensation to evaluate the facilitation in pain processing at spinal level. Fifteen (7 Women; 8 Men; mean age 63.0 ± 9.1) Parkinson's disease patients without clinical pain and 12 (6 Women, 6 Men; mean age 61.2 ± 4.2) healthy subjects were recruited. Parkinson's disease group has been subdivided into two subgroups, 7 early-stage Parkinson's disease patients with unilateral signs (Hoehn and Yahr stage 1) and 8 patients in a more advanced stage of the disease showing bilateral parkinsonian signs (Hoehn and Yahr stages 2 and 2.5), both "on" and "off" treatments with levodopa.

RESULTS

A significant facilitation in temporal summation of pain (reduced temporal summation threshold and increased painful sensation) was found in Parkinson's disease patients when compared with controls. This facilitation is more evident in Parkinson's disease with bilateral signs and on the side more affected in Parkinson's disease with unilateral signs. Levodopa administration failed to significantly modify the neurophysiological abnormalities; however, a slight improvement has been detected.

CONCLUSIONS

The increased gain in pain processing at spinal level in Parkinson's disease patients could be a consequence of the degenerative phenomena involving supraspinal projections implicated in the modulation of pain processing and could make Parkinson's disease patients more predisposed to develop a pain condition.

[Nociceptive system : Nociceptors, fiber types, spinal pathways, and projection areas]

In order to transform a nociceptive stimulus into a painful perception, a highly specialized chain of structural and functional elements is necessary. This system comprises nociceptors in the periphery with specific molecular properties for differential coding of noxious submodalities, ascending and descending tracts that can control the input into the dorsal horn of the spinal cord as well as supraspinal processing that regulates the integration of nociceptive information with other sensory modalities and autonomic function. In this article, structures involved in nociceptive signal processing starting from the periphery up to spinal and cerebral structures are discussed in the order of their spatio-temporal activation sequence - as far as these are known. Already from the basis of the different receptor subtypes found on the thinly or unmyelinated nerve fibers in the periphery, the predominant principle of polymodality is demonstrated. Different input to the dorsal horn of the spinal cord by different nerve fiber populations to superficial and deep layers is explained, ascending tracts as well as descending systems capable of either facilitating or inhibiting the upstream flow of nociceptive information, together with their known transmitters. Finally, thalamic relay nuclei for sensory and nociceptive signals, as well as subcortical and cortical projection targets are discussed. To complete the current view of the nociceptive system, information from molecular biology and anatomic tracing studies as well as data from functional electrophysiologic cell recordings in animals and imaging studies in humans are assembled.