Pains in Parkinson disease—many syndromes under one umbrella

Pain processing in atypical Parkinsonisms and Parkinson disease: A comparative neurophysiological study

OBJECTIVE

Pain is a frequent non-motor feature in Parkinsonism but mechanistic data on the alteration of pain processing are insufficient to understand the possible causes and to define specifically-targeted treatments.

METHODS

we investigated spinal nociception through the neurophysiological measure of the threshold (TR) of nociceptive withdrawal reflex (NWR) and its temporal summation threshold (TST) comparatively in 12 Progressive Supranuclear Palsy (PSP) subjects, 11 Multiple System Atrophy (MSA) patients, 15 Parkinson's disease (PD) subjects and 24 healthy controls (HC). We also investigated the modulatory effect of L-Dopa in these three parkinsonian groups.

RESULTS

We found a significant reduction in the TR of NWR and in the TST of NWR in PSP, MSA and PD patients compared with HC. L-Dopa induced an increase in the TR of NWR in the PSP group while TST of NWR increased in both PSP and PD.

CONCLUSIONS

Our neurophysiological findings identify a facilitation of nociceptive processing in PSP that is broadly similar to that observed in MSA and PD. Specific peculiarities have emerged for PSP.

SIGNIFICANCE

Our data advance the knowledge of the neurophysiology of nociception in the advanced phases of parkinsonian syndromes and on the role of dopaminergic pathways in the control on pain processing.

Nonmotor Effects of Conventional and Transdermal Dopaminergic Therapies in Parkinson's Disease

Nonmotor symptoms (NMS) are an integral component of Parkinson's disease (PD). Because the burden and range of NMS are key determinants of quality of life for patients and caregivers, their management is a crucial issue in clinical practice. Although a range of NMS have a dopaminergic pathophysiological basis, this fact is underrecognized, and thus, they are often regarded as dopamine unresponsive symptoms. However, substantial evidence indicates that many NMS respond to oral and transdermal dopaminergic therapies. In contrast, certain NMS are exacerbated or even precipitated by dopaminergic drugs and these unwanted effects may be seriously dangerous. Therefore, a dopaminergic strategy for NMS should be based on a consideration of the benefits vs the risks in individual patients with PD.

Non-motor features of Parkinson disease

Many of the motor symptoms of Parkinson disease (PD) can be preceded, sometimes for several years, by non-motor symptoms that include hyposmia, sleep disorders, depression and constipation. These non-motor features appear across the spectrum of patients with PD, including individuals with genetic causes of PD. The neuroanatomical and neuropharmacological bases of non-motor abnormalities in PD remain largely undefined. Here, we discuss recent advances that have helped to establish the presence, severity and effect on the quality of life of non-motor symptoms in PD, and the neuroanatomical and neuropharmacological mechanisms involved. We also discuss the potential for the non-motor features to define a prodrome that may enable the early diagnosis of PD.

Diagnostic confounders of chronic widespread pain: not always fibromyalgia

Although chronic widespread pain is the defining feature of fibromyalgia, a myriad of other conditions may present with similar pain complaint leading to misdiagnosis. Conditions that may mimic fibromyalgia may be categorized as musculoskeletal, neurological, endocrine/metabolic, psychiatric/psychological, and medication related. In this review, we examine these various conditions that should be considered in a differential diagnosis and provide direction that will help the clinician differentiate these conditions from fibromyalgia.

Introduction:

Chronic widespread pain (CWP) is the defining feature of fibromyalgia (FM), a worldwide prevalent condition. Chronic widespread pain is, however, not pathognomonic of FM, and other conditions may present similarly with CWP, requiring consideration of a differential diagnosis.

Objectives:

To conduct a literature search to identify medical conditions that may mimic FM and have highlighted features that may differentiate these various conditions from FM.

Methods:

A comprehensive literature search from 1990 through September 2016 was conducted to identify conditions characterized by CWP.

Results:

Conditions that may mimic FM may be categorized as musculoskeletal, neurological, endocrine/metabolic, psychiatric/psychological, and medication related. Characteristics pertaining to the most commonly identified confounding diagnoses within each category are discussed; clues to enable clinical differentiation from FM are presented; and steps towards a diagnostic algorithm for mimicking conditions are presented.

Conclusion:

Although the most likely reason for a complaint of CWP is FM, this pain complaint can be a harbinger of illness other than FM, prompting consideration of a differential diagnosis. This review should sensitize physicians to a broad spectrum of conditions that can mimic FM.

Distribution and impact on quality of life of the pain modalities assessed by the King's Parkinson's disease pain scale

In Parkinson’s disease, pain is a prevalent and complex symptom of diverse origin. King’s Parkinson’s disease pain scale, assesses different pain syndromes, thus allowing exploration of its differential prevalence and influence on the health-related quality of life of patients. Post hoc study 178 patients and 83 matched controls participating in the King’s Parkinson’s disease pain scale validation study were used. For determining the respective distribution, King’s Parkinson’s disease pain scale items and domains scores = 0 meant absence and ≥1 presence of the symptom. The regular scores were used for the other analyses. Health-related quality of lifewas evaluated with EQ-5D-3L and PDQ-8 questionnaires. Parkinson’s disease patients experienced more pain modalities than controls. In patients, Pain around joints (King’s Parkinson’s disease pain scale item 1) and Pain while turning in bed (item 8) were the most prevalent types of pain, whereas Burning mouth syndrome (item 11) and Pain due to grinding teeth (item 10) showed the lowest frequency. The total number of experienced pain modalities closely correlated with the PDQ-8 index, but not with other variables. For all pain types except Pain around joints (item 1) and pain related to Periodic leg movements/RLS (item 7), patients with pain had significantly worse health-related quality of life. The influence of pain, as a whole, on the health-related quality of life was not remarkable after adjustment by other variables. When the particular types of pain were considered, adjusted by sex, age, and Parkinson’s disease duration, pain determinants were different for EQ-5D-3L and PDQ-8. King’s Parkinson’s disease pain scale allows exploring the distribution of the diverse syndromic pain occurring in Parkinson’s disease and its association with health-related quality of life.

Researchers confirm that the pain experienced by patients with Parkinson disease (PD) is a key determinant of health-related quality of life. Pain is a common non-motor symptom that is often underacknowledged and undertreated. Using data from the recently validated pain scale for PD, Pablo Martinez-Martin (Carlos III Institute of Health in Madrid, Spain) and colleagues explored the impact of specific pain modalities on patients’ quality of life. They found that patients with PD reported experiencing twice as many types of pain than controls, with pain around the joints and pain while moving in bed being the most prevalent. Furthermore, there was a close correlation between the number of experienced pain modalities and quality of life as evaluated with the PD questionnaire PDQ-8. Understanding the different types of pain in PD will aid the provision of effective pain relief and greatly improve patients’wellbeing.

[Pain - a neglected neurological issue]

Chronic pain represents a great challenge; according to epidemiological data increasing numbers of patients should be expected. Based on recent advances, a better understanding of the pathophysiology of chronic pain has been achieved and neurologists have made a major contribution to this understanding. Chronic pain is accompanied by substantial maladaptive plastic alterations in both the peripheral and central nervous systems; therefore, neurological knowledge is of paramount importance for pain therapists but this contrasts with the current treatment situation of pain patients in Germany. There are basically too few departments and practices undertaking treatment, and neurologists are an exception in most pain centers. Furthermore, due to economic reasons neurological hospitals are currently experiencing a dearth of inpatients suffering from chronic pain. Diagnostic and/or treatment procedures for neurological pain entities (e.g. headaches or neuropathic pain) are insufficiently represented in the German diagnosis-related groups (DRG) reimbursement system and the obstacles for an efficient pain therapy in neurological practices are too high. Finally, there are too few academic positions for pain medicine in neurological hospitals; therefore, career opportunities for motivated young neurologists with an interest in pain are lacking. In order to address the unmet therapeutic needs of patients with chronic pain there is a high demand for (i) establishment of departments for neurological pain medicine, (ii) modification of the German DRG system and (iii) education of young neurologists with expertise in pain. Pain medicine in particular should be especially appealing to neurologists .

Clinical Determinants of Parkinson's Disease-associated Pain Using the King's Parkinson's Disease Pain Scale

Background

Pain is a frequent feature in Parkinson's disease (PD). Current knowledge on pain and its associated factors in PD has been obtained using nondisease-specific tools. Recently, the King's Parkinson's Disease Pain Scale (KPPS) was published as the first disease-specific scale. The aim of this study was to assess PD-associated pain and its main determinants using the KPPS.

Methods

A cross-sectional study was carried out. Consecutive patients with PD were recruited from a movement disorders clinic. Clinical and demographical data were collected. The KPPS, the Movement Disorders Society Unified Parkinson's Disease Rating Scale, and the Non-Motor Symptoms Scale were used to assess all participants.

Results

In total, 314 patients were included. Overall, 88.6% of the sample reported at least 1 type of pain. The mean ± standard KPPS score was 18.8 ± 19.5. Factors associated with higher KPSS scores were female sex (P < 0.001), levodopa treatment (P < 0.001), the presence of depressed mood (P < 0.001), wearing off (P = 0.003), and dyskinesia (P = 0.005). Participants who had postural instability and gait difficulty motor subtypes had higher KPPS scores compared with those who had other subtypes. Multivariate regression analysis showed that only sex, motor subtype, depressed mood, and Non-Motor Symptoms Scale sleep/fatigue domain scores achieved statistical significance as determinants (all P < 0.01).

Conclusion

PD-associated pain is a frequent symptom that tends to increase in both frequency and severity as disease progresses. Risk factors for increased burden include female gender, postural instability and gait difficulty motor subtypes, mood alterations, and sleep/fatigue disturbances.

Safinamide: A Review in Parkinson's Disease

Safinamide (Xadago^®) is an orally active, selective, reversible monoamine oxidase-B inhibitor with both dopaminergic and non-dopaminergic (glutamatergic) properties. In the EU, safinamide is approved for the treatment of mid- to late-stage fluctuating Parkinson's disease (PD) as add-on therapy to a stable dose of levodopa alone or in combination with other PD medications. Safinamide 50-100 mg/day administered as a fixed or flexible dose significantly increased daily 'on' time without dyskinesia (primary endpoint) in patients with mid- to late-stage PD with motor fluctuations in 24-week, placebo-controlled clinical trials. Other outcomes, including motor function, overall clinical status and health-related quality of life, were also generally improved with safinamide. Furthermore, in an 18-month extension of one study, although dyskinesia (primary endpoint) was not significantly improved with safinamide relative to placebo, treatment benefits in other outcomes were generally sustained over 24 months of treatment. Safinamide was generally well tolerated in clinical trials; dyskinesia was the most common adverse event. Although further studies are needed, including comparative and long-term studies, current evidence indicates that safinamide extends the treatment options available for use as add-on therapy to levodopa and other PD medications in patients with mid- to late-stage PD experiencing motor fluctuations.

Rating Scales for Pain in Parkinson's Disease: Critique and Recommendations

BACKGROUND

We aimed at critically appraising the clinimetric properties of existing pain scales or questionnaires and to give recommendations for their use in Parkinson's disease (PD).

METHODS

Clinimetric properties of pain scales used in PD were systematically evaluated. A scale was classified as 'recommended' if was used in PD, showed adequate clinimetric properties, and had been used by investigators other than the original developers; as 'suggested' if it was used in PD and fulfilled only one other criterion; and as 'listed' if it was used in PD but did not meet the other criteria. Only scales rating pain intensity or for syndromic classification were assessed.

RESULTS

Eleven of the 34 scales initially considered fulfilled inclusion criteria. Among the scales rating pain intensity, the "Brief Pain Inventory short form," "McGill Pain Questionnaire short and long forms," "Neuropathic Pain Symptoms Inventory," "11-point Numeric Rating Scale," "10-cm Visual Analog Scale," and "Pain-O-Meter" were "recommended with caution" because of lack of clinimetric data in PD, whereas the "King's PD Pain Scale" was "recommended." Among scales for pain syndromic classification, the "DN4" was "recommended with caution" because of lack of clinimetric data in PD; the "Leeds Assessment of Neuropathic Symptoms and Signs," "Pain-DETECT," and the "King's PD Pain Scale" were "suggested."

CONCLUSIONS

King's PD pain scale can be recommended for the assessment of pain intensity in PD. Syndromic classification of pain in PD may be achieved by the DN4, but clinimetric data in PD are needed for this scale.

Effects of subthalamic deep brain stimulation with duloxetine on mechanical and thermal thresholds in 6OHDA lesioned rats

Chronic pain is the most common non-motor symptom of Parkinson's disease (PD) and is often overlooked. Unilateral 6-hydroxydopamine (6-OHDA) medial forebrain bundle lesioned rats used as models for PD exhibit decreased sensory thresholds in the left hindpaw. Subthalamic deep brain stimulation (STN DBS) increases mechanical thresholds and offers improvements with chronic pain in PD patients. However, individual responses to STN high frequency stimulation (HFS) in parkinsonian rats vary with 58% showing over 100% improvement, 25% showing 30-55% improvement, and 17% showing no improvement. Here we augment STN DBS by supplementing with a serotonin-norepinephrine reuptake inhibitor commonly prescribed for pain, duloxetine. Duloxetine was administered intraperitoneally (30mg/kg) in 15 parkinsonian rats unilaterally implanted with STN stimulating electrodes in the lesioned right hemisphere. Sensory thresholds were tested using von Frey, Randall-Selitto and hot-plate tests with or without duloxetine, and stimulation to the STN at HFS (150Hz), low frequency (LFS, 50Hz), or off stimulation. With HFS or LFS alone (left paw; p=0.016; p=0.024, respectively), animals exhibited a higher mechanical thresholds stable in the three days of testing, but not with duloxetine alone (left paw; p=0.183). Interestingly, the combination of duloxetine and HFS produced significantly higher mechanical thresholds than duloxetine alone (left paw, p=0.002), HFS alone (left paw, p=0.028), or baseline levels (left paw; p<0.001). These findings show that duloxetine paired with STN HFS increases mechanical thresholds in 6-OHDA-lesioned animals more than either treatment alone. It is possible that duloxetine augments STN DBS with a central and peripheral additive effect, though a synergistic mechanism has not been excluded.

Clinical Definition of Camptocormia in Parkinson's Disease

Background

Clinical key aspects of camptocormia in patients with idiopathic Parkinson's disease (PD) await further definition.

Methods

Based on a self-assessment of PD patients, we performed an observational study, asking patients with subjectively felt involuntary forward bending to return a questionnaire and provide photographs showing their axial disorder. Forty-two matched PD patients without subjective signs of camptocormia were recruited as controls.

Results

The stooped posture of patients with advanced PD without camptocormia is characterized by a forward bending angle of always less than 30 degrees. Of the 145 camptocormia patients in our study, 70% had an angle ≥30 degrees. The patients with a more-severe forward bending angle were more severely affected in daily life than those with an angle of less than 30 degrees. Back pain was more frequent (81% vs. 43%) and more severe in PD patients with camptocormia than in controls. Back diseases in camptocormia PD patients were also significantly more frequent than in the PD control patients (55% vs. 26%). Camptocormia is a relevant burden in everyday life. Seventy-seven percent of patients needed walking aids and 85% reported specific disabilities attributed to camptocormia (e.g. increased risk of falling, dyspnea, problems in eating or swallowing).

Conclusions

Camptocormia cannot be clinically defined based on the forward bending angle alone, but an angle larger than 30 degrees is only found in camptocormia. Back pain is an essential aspect of camptocormia in PD. Back diseases can be seen as a risk factor in these patients.

Classification and Characteristics of Pain Associated with Parkinson's Disease

Neuropsychiatric symptoms and pain are among the most common nonmotor symptoms of Parkinson's disease (PD). The correlation between pain and PD has been recognized since its classic descriptions. Pain occurs in about 60% of PD patients, two to three times more frequent in this population than in age matched healthy individuals. It is an early and potentially disabling symptom that can precede motor symptoms by several years. The lower back and lower extremities are the most commonly affected areas. The most used classification for pain in PD defines musculoskeletal, dystonic, central, or neuropathic/radicular forms. Its different clinical characteristics, variable relationship with motor symptoms, and inconsistent response to dopaminergic drugs suggest that the mechanism underlying pain in PD is complex and multifaceted, involving the peripheral nervous system, generation and amplification of pain by motor symptoms, and neurodegeneration of areas related to pain modulation. Although pain in DP is common and a significant source of disability, its clinical characteristics, pathophysiology, classification, and management remain to be defined.

Contribution of Pro-inflammatory Cytokine Signaling within Midbrain Periaqueductal Gray to Pain Sensitivity in Parkinson's Disease via GABAergic Pathway

Background/aims

Hypersensitive pain response is often observed in patients with Parkinson’s disease (PD); however, the mechanisms responsible for hyperalgesia are not well understood. Chronic neuroinflammation is one of the hallmarks of PD pathophysiology. Since the midbrain periaqueductal gray (PAG) is an important component of the descending inhibitory pathway controlling on central pain transmission, we examined the role for pro-inflammatory cytokines (PICs) system of PAG in regulating exaggerated pain evoked by PD.

Methods

We used a rat model of PD to perform the experimental protocols. PD was induced by microinjection of 6-hydroxydopamine to lesion the left medial forebrain bundle. Pain responses to mechanical and thermal stimulation were first examined in control rats and PD rats. Then, ELISA and Western Blot analysis were used to determine PIC levels and their receptors expression.

Results

Protein expression of IL-1β, IL-6, and TNF-α receptors (namely, IL-1R, IL-6R, and TNFR subtype TNFR1) in the plasma membrane PAG of PD rats was upregulated, whereas the total expression of PIC receptors was not significantly altered. The ratio of membrane protein and total protein (IL-1R, IL-6R, and TNFR1) was 1.48 ± 0.15, 1.59 ± 0.18, and 1.67 ± 0.16 in PAG of PD rats (P < 0.05 vs. their respective controls). This was accompanied with increases of PICs of PAG and decreases of GABA (623 ± 21 ng/mg in control rats and 418 ± 18 ng/mg in PD rats; P < 0.05 vs. control rats) and withdrawal thresholds to mechanical and thermal stimuli. Our data further showed that the concentrations of GABA and withdrawal thresholds were largely restored by blocking those PIC receptors in PAG of PD rats. Stimulation of GABA receptors in PAG of PD rats also blunted a decrease in withdrawal thresholds.

Conclusion

Our data suggest that upregulation of the membrane PIC receptor in the PAG of PD rats is likely to impair the descending inhibitory pathways in regulating pain transmission and thereby plays a role in the development of hypersensitive pain response in PD.

Dopamine in plasma - a biomarker for myofascial TMD pain?

Background

Dopaminergic pathways could be involved in the pathophysiology of myofascial temporomandibular disorders (M-TMD). This study investigated plasma levels of dopamine and serotonin (5-HT) in patients with M-TMD and in healthy subjects.

Methods

Fifteen patients with M-TMD and 15 age- and sex-matched healthy subjects participated. The patients had received an M-TMD diagnosis according to the Research Diagnostic Criteria for TMD. Perceived mental stress, pain intensity (0–100-mm visual analogue scale), and pressure pain thresholds (PPT, kPa) over the masseter muscles were assessed; a venous blood sample was taken.

Results

Dopamine in plasma differed significantly between patients with M-TMD (4.98 ± 2.55 nM) and healthy controls (2.73 ± 1.24 nM; P < 0.01). No significant difference in plasma 5-HT was observed between the groups (P = 0.75). Patients reported significantly higher pain intensities (P < 0.001) and had lower PPTs (P < 0.01) compared with the healthy controls. Importantly, dopamine in plasma correlated significantly with present pain intensity (r = 0.53, n = 14, P < 0.05) and perceived mental stress (r = 0.34, n = 28, P < 0.05).

Conclusions

The results suggest that peripheral dopamine might be involved in modulating peripheral pain. This finding, in addition to reports in other studies, suggests that dopaminergic pathways could be implicated in the pathophysiology of M-TMD but also in other chronic pain conditions. More research is warranted to elucidate the role of peripheral dopamine in the pathophysiology of chronic pain.

The Rationale for Exercise in the Management of Pain in Parkinson's Disease

Pain is a distressing non-motor symptom experienced by up to 85% of people with Parkinson’s disease (PD), yet it is often untreated. This pain is likely to be influenced by many factors, including the disease process, PD impairments as well as co-existing musculoskeletal and/or neuropathic pain conditions. Expert opinion recommends that exercise is included as one component of pain management programs; however, the effect of exercise on pain in this population is unclear. This review presents evidence describing the potential influence of exercise on the pain-related pathophysiological processes present in PD. Emerging evidence from both animal and human studies suggests that exercise might contribute to neuroplasticity and neuro-restoration by increasing brain neurotrophic factors, synaptic strength and angiogenesis, as well as stimulating neurogenesis and improving metabolism and the immune response. These changes may be beneficial in improving the central processing of pain. There is also evidence that exercise can activate both the dopaminergic and non-dopaminergic pain inhibitory pathways, suggesting that exercise may help to modulate the experience of pain in PD. Whilst clinical data on the effects of exercise for pain relief in people with PD are scarce, and are urgently needed, preliminary guidelines are presented for exercise prescription for the management of central neuropathic, peripheral neuropathic and musculoskeletal pain in PD.

Chronic pain in Parkinson's disease: Frequency, characteristics, independent factors, and relationship with health-related quality of life

BACKGROUND

Although there are studies evaluating pain in Parkinson's disease (PD), to our knowledge, there is no study evaluating the following topics in a cohort of PD patients; (1) frequency of chronic pain, (2) characteristics of chronic pain, (3) severity of chronic pain, (4) types of chronic pain, (5) independent predictors of chronic pain, (6) impact of chronic pain on health-related quality of life (HRQoL), and (7) the role of chronic pain among the independent predictors of HRQoL.

OBJECTIVE

The purpose of this study was to evaluate the frequency, characteristics, severity, types, and independent factors of chronic pain, as well as the relationship of chronic pain with HRQoL in a cohort of PD patients.

METHODS

One-hundred and thirteen individuals with a confirmed diagnosis of PD who were consecutively referred to the Ministry of Health Ankara Diskapi Yildirim Beyazit Training and Research Hospital, Movement Disorders Outpatient Clinic were included in the study. Demographic variables, disease characteristics, disease-related motor symptoms and motor complications, comorbid conditions, and health-related quality of life were evaluated and recorded. Pain lasting longer than three months was defined as `chronic pain' and participants were questioned relating to the characteristics of the chronic pain. The Visual Analogue Scale was used for assessment of pain.

RESULTS

Seventy-three patients (64.6%) suffered from chronic pain. Of these, 12 (16.4%) had previous pain at the time of diagnosis of PD. The sources of pain experienced by patients were 89.0% musculoskeletal, 31.5% radicular/peripheral neuropathic, 15.1% dystonic, and 4.1% central parkinsonian, respectively. Twenty-six patients (35.6%) had different types of pain simultaneously. The pain type with the highest severity was a central parkinsonian pain.The independent predictors of chronic pain included gender (female), Unified Parkinson's Disease Rating Scale (UPDRS) part II (activities of daily living), UPDRS part III (motor symptoms) rigidity subscore, and depression.When compared with individuals not having chronic pain, Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Physical Component Summary and Mental Component Summary scores were lower in patients with chronic pain. Also, it was shown that the most significant factor on SF-36 was chronic pain.

CONCLUSIONS

This study demonstrated that chronic pain is a common problem in patients with PD, that different pain types may co-exist, and that they may negatively affect the HRQoL of patients. Chronic pain was correlated with both disease-related factors such as rigidity and daily living activities and also general factors such as gender and depression. We found that chronic pain is the most significant predictor of quality of life in PD patients. We believe, that in addition to treating motor symptoms and complications associated with them, treatment of comorbid conditions such as pain and depression bear significance for improving the quality of life in PD patients. The study indicates that PD patients who are optimally treated, may require additional rehabilitation treatment for non-motor associated pain and thus improve their HRQoL.

Microbiota-gut-brain signalling in Parkinson's disease: Implications for non-motor symptoms

Parkinson's disease is the second most common neurodegenerative disorder, affecting 1-2% of the population over 65 years of age. The primary neuropathology is the loss of midbrain dopaminergic neurons, resulting in characteristic motor deficits, upon which the clinical diagnosis is based. However, a number of significant non-motor symptoms (NMS) are also evident that appear to have a greater impact on the quality of life of these patients. In recent years, it has become increasingly apparent that neurobiological processes can be modified by the bi-directional communication that occurs along the brain-gut axis. The microbiota plays a key role in this communication throughout different routes in both physiological and pathological conditions. Thus, there has been an increasing interest in investigating how microbiota changes within the gastrointestinal tract may be implicated in health and disease including PD. Interestingly α-synuclein-aggregates, the cardinal neuropathological feature in PD, are present in both the submucosal and myenteric plexuses of the enteric nervous system, prior to their appearance in the brain, indicating a possible gut to brain route of "prion-like" spread. In this review we highlight the potential importance of gut to brain signalling in PD with particular focus on the role of the microbiota as major player in this communication.

The Association Between Parkinson's Disease Motor Impairments and Pain

OBJECTIVE

This study aimed to: 1) examine the severity and frequency of pain and the extent to which pain interferes with work and 2) explore the contributions of motor impairments to pain in people with Parkinson's disease (PD).

METHOD

Pain severity, frequency and the impact of pain on work were determined using subscores from the SF-36^TM, Parkinson's Disease Questionnaire and SF-12v2^TM, respectively, in 231 people with Parkinson's disease. Motor impairments were measured using the Unified Parkinson's Disease Rating Scale. Freezing of gait was determined as its presence or absence in the last month. Associations between impairments and pain were examined using logistic regression.

RESULTS

Pain was reported by 187 (81%) participants, with 91 (39%) reporting pain of moderate severity or worse. Pain interfered with work to some extent in 158 (68%) participants. After adjusting for age and gender, increased rigidity was associated with higher pain frequency and more pain that interfered with work (for both models, Odds Ratio = 1.14, 95% confidence interval 1.0-1.3). Tremor was not associated with any measures of pain and motor impairments were not associated with pain severity.

CONCLUSIONS

Most people with PD experience pain at least monthly and pain interferes with daily activities. PD impairments are associated with more frequent pain and pain that interferes with work, with rigidity having the strongest association. Development of Parkinson's disease-specific pain assessments and further investigation into the association between PD impairments and pain is warranted.

A Randomized Controlled Exploratory Pilot Study to Evaluate the Effect of Rotigotine Transdermal Patch on Parkinson's Disease-Associated Chronic Pain

Pain is a troublesome nonmotor symptom of Parkinson's disease (PD). This double-blind exploratory pilot study (NCT01744496) was the first to specifically investigate the effect of a dopamine agonist on PD-associated pain as primary outcome. Patients with advanced PD (ie, receiving levodopa) and at least moderate PD-associated chronic pain (≥3 months, ≥4 points on 11-point Likert pain scale) were randomized to rotigotine (optimal/maximum dose ≤16 mg/24h) or placebo and maintained for 12 weeks. Primary efficacy variable was change in pain severity (Likert pain scale) from baseline to end of maintenance. Secondary variables included percentage of responders (≥2-point Likert pain scale reduction), King's PD Pain Scale (KPPS) domains, and PD Questionnaire (PDQ-8). Statistical analyses were exploratory. Of 68 randomized patients, 60 (rotigotine, 30; placebo, 30) were evaluable for efficacy. A numerical improvement in pain was observed in favor of rotigotine (Likert pain scale: least-squares mean [95%CI] treatment difference, -0.76 [-1.87 to 0.34]; P = .172), and proportion of responders was 18/30 (60%) rotigotine vs 14/30 (47%) placebo. An ∼2-fold numerical improvement in KPPS domain "fluctuation-related pain" was observed with rotigotine vs placebo. Rotigotine improved PDQ-8 vs placebo (-8.01 [-15.56 to -0.46]; P = .038). These results suggest rotigotine may improve PD-associated pain; a large-scale confirmatory study is needed.

Prolonged-release oxycodone-naloxone for treatment of severe pain in patients with Parkinson's disease (PANDA): a double-blind, randomised, placebo-controlled trial

BACKGROUND

Pain is a common non-motor symptom of Parkinson's disease. We investigated the analgesic efficacy of prolonged-release oxycodone-naloxone (OXN PR) in patients with Parkinson's disease and chronic, severe pain.

METHODS

We did this phase 2 study in 47 secondary care centres in the Czech Republic, Germany, Hungary, Poland, Romania, Spain, and the UK. We enrolled patients with Hoehn and Yahr Stage II-IV Parkinson's disease, at least one type of severe pain, and an average 24-h pain score of at least 6 (assessed on an 11-point rating scale from 0=no pain to 10=pain as bad as you can imagine). Participants were randomly assigned (1:1) with a validated automated system (block size four) to either oral OXN PR or placebo for 16 weeks (starting dose oxycodone 5 mg, naloxone 2·5 mg, twice daily). Patients and investigators were masked to treatment assignment. The primary endpoint was average 24-h pain score at 16 weeks in the full analysis population. This study is registered with EudraCT (2011-002901-31) and ClinicalTrials.gov (NCT01439100).

FINDINGS

We enrolled 202 patients; 93 were assigned to OXN PR and 109 to placebo; the full analysis population consisted of 88 patients versus 106 patients. Least squares mean average 24-h pain score at 16 weeks in the full analysis population was 5·0 (95% CI 4·5 to 5·5) in the OXN PR group versus 5·6 (5·1 to 6·0) in the placebo group (difference -0·6, 95% CI -1·3 to 0·0; p=0·058). Similar proportions of patients in each group had adverse events (60/92 [65%] vs 76/109 [70%]), treatment-related adverse events (52/92 [57%] vs 62/109 [57%]), and serious adverse events (5/92 [5%] vs 7/109 [6%]). Treatment-related nausea was more common in the OXN PR group than in the placebo group (16/92 [17%] vs 10/109 [9%]), as was treatment-related constipation (16/92 [17%] vs 6/109 [6%]).

INTERPRETATION

The primary endpoint, based on the full analysis population at week 16, was not significant. Nonetheless, the results of this study highlight the potential efficacy of OXN PR for patients with Parkinson's disease-related pain and might warrant further research on OXN PR in this setting.

FUNDING

Mundipharma Research.

Pain in Parkinson's Disease: A Cross-Sectional Study of Its Prevalence, Types, and Relationship to Depression and Quality of Life

Pain is an important and distressing symptom in Parkinson's disease (PD). Our aim was to determine the prevalence of pain, its various types and characteristics, as well as its impact on depression and quality of life (QoL) in patients with PD. How pain differs in early- and advanced-stage PD and male and female PD patients was of special interest. One hundred PD patients on dopaminergic medications had a neurological examination and participated in a structured interview on pain characteristics and completed standardized questionnaires. A total of 76% of the patients had pain. The following types of pain were present: musculoskeletal pain accounted for 41% of the total pain, dystonic pain for 17%, central neuropathic pain for 22%, radicular pain for 27%, and other pains (non-radicular low back pain, arthritic, and visceral pain) made up 24%. One type of pain affected 29% of all the subjects, two types 35%, three types 10%, and four types of pain were reported by 2%. All types of pain were more prevalent in advanced-stage PD subjects than in early-stage PD subjects, except for arthritic pain (subclassified under"other pain"). The frequency and intensity of actual, average, and worst experienced pain were significantly more severe in advanced-stage subjects. PD subjects with general pain and in advanced stages were more depressed and had poorer QoL. Depression correlated with worst pain in the last 24 hours and with pain periodicity (the worst depression score in patients with constant pain). QoL correlated with average pain in the last 7 days. Pain is a frequent problem in PD patients, and it worsens during the course of the disease.

Alteration of Basal Ganglia and Right Frontoparietal Network in Early Drug-Naïve Parkinson's Disease during Heat Pain Stimuli and Resting State

Background

The symptoms and pathogenesis of Parkinson’s disease (PD) are complicated and an accurate diagnosis of PD is difficult, particularly in early-stage. Because functional magnetic resonance imaging (fMRI) is non-invasive and is characterized by the integration of different brain areas in terms of functional connectivity (FC), fMRI has been widely used in PD research. Non-motor symptom (NMS) features are also frequently present in PD before the onset of classical motor symptoms with pain as the primary NMS. Considering that PD could affect the pain process at multiple levels, we hypothesized that pain is one of the earliest symptoms in PD and investigated whether FC of the pain network was disrupted in PD without pain. To better understand the pathogenesis of pain in PD, we combined resting state and pain-stimuli-induced task state fMRI to identify alterations in FC related to pain in PD.

Methods

Fourteen early drug-naïve PD without pain and 17 age- and sex-matched healthy controls (HC) participated in our testing task. We used independent component analysis to select seven functional networks related to PD and pain. We focused on abnormalities in FC and in functional network connectivity (FNC) in PD compared with HC during the task (51°C heat pain stimuli) and at rest.

Results

Compared with HC, PD showed decreased FC in putamen within basal ganglia network (BGN) in task state and decreased FC in putamen of salience network (SN) and mid-cingulate cortex of sensorimotor network in rest state. FNC between the BGN and the SN are reduced during both states in PD compared with HC. In addition, right frontoparietal network (RFPN), which is considered as a bridge between the SN and default-mode network, was significantly disturbed during the task.

Conclusion

These findings suggest that BGN plays a role in the pathological mechanisms of pain underlying PD, and RFPN likely contributes greatly to harmonization between intrinsic brain activity and external stimuli.

Pain in Parkinson's Disease: Current Concepts and a New Diagnostic Algorithm

Background

Pain is a significant burden for patients with Parkinson's disease (PD) with a high impact on quality of life. The present article aims at summarizing epidemiological, pathophysiological, clinical, and neurophysiological data regarding pain in PD.

Methods

In this domain, a procedure of systematic assessment is still lacking for the syndromic diagnosis and should take into account pain characteristics, effects of dopaminergic treatment, motor fluctuations, and non-PD-associated pain.

Findings

We propose an original questionnaire addressing an algorithm suitable for daily clinical practice. The questionnaire is based on a three-step approach addressing first the relationship between pain and PD (including temporal relationship with the course of the disease, association with motor fluctuations, and impact of antiparkinsonian treatment), before classifying pain into one of three main syndromes (i.e., musculoskeletal pain, psychomotor restlessness pain, and neuropathic pain).

Conclusions

The proposed questionnaire allows the characteristics of each pain type to be determined according to its relationship with the disease and its treatment. The validation of the clinical use of this questionnaire will be the goal of a forthcoming work.

Is excessive daytime sleepiness a separate manifestation in Parkinson's disease?

BACKGROUND

Excessive daytime sleepiness (EDS) is common in Parkinson's disease (PD), but its role and relation to other PD features is less well understood.

OBJECTIVE

To investigate potential predictors of EDS in PD and to explore how EDS relates to other motor and non-motor PD features.

METHODS

118 consecutive persons with PD (54% men; mean age, 64) were assessed regarding EDS using the Epworth Sleepiness Scale (ESS) and a range of motor and non-motor symptoms. Variables significantly associated with ESS scores in bivariate analyses were used in multiple regression analyses with ESS scores as the dependent variable. Principal component analysis (PCA) was conducted to explore the interrelationships between ESS scores and other motor and non-motor PD aspects.

RESULTS

Among 114 persons with complete ESS data, significant independent associations were found between ESS scores and axial/postural/gait impairment, depressive symptoms, and pain (R2, 0.199). ESS scores did not load significantly together with any other PD features in the PCA.

CONCLUSIONS

Only a limited proportion of the variation in EDS could be accounted for by other symptoms, and EDS did not cluster together with any other PD features in PCAs. This suggests that EDS is a separate manifestation differing from, for example, poor sleep quality and fatigue.

Pain in multiple system atrophy and progressive supranuclear palsy compared to Parkinson's disease

BACKGROUND

Pain is a common nonmotor symptom in Parkinson's disease (PD). The pathophysiology of pain in PD is not well understood. Pain characteristics have rarely been studied in atypical parkinsonian disorders such as Multiple System Atrophy (MSA) and Progressive Supranuclear Palsy (PSP).

AIM OF THE STUDY

We aimed to evaluate pain intensity, location, and associated symptoms in atypical parkinsonian disorders compared to PD.

METHODS

Twenty-one patients with MSA, 16 patients with PSP, and 65 patients with PD were screened for pain using question 1.9 of the MDS-UPDRS. Pain intensity was quantified using the short form McGill Pain Questionnaire (SFMPQ). Pain locations were documented. Motor disability was measured using UPDRS-III. Affective symptoms were assessed using the Hospital Anxiety and Depression Scale (HADS).

RESULTS

Pain was significantly more common and more severe in PD and MSA compared to PSP (P < 0.01). Pain locations were similar with limb pain being the most common followed by neck and back pain. Pain intensity correlated with HADS scores but not motor severity.

CONCLUSIONS

Pain is more common and more intense in PD and MSA than PSP. Differences in distribution of neurodegenerative pathologies may underlie these differential pain profiles.

Lesion of the dopaminergic nigrostriatal pathway induces trigeminal dynamic mechanical allodynia

BACKGROUND

Pain constitutes the major non motor syndrome in Parkinson's disease (PD) and includes neuropathic pain; however current drug therapies used to alleviate it have only limited efficacy. This is probably due to poor understanding of the mechanisms underlying it.

AIMS

We investigated a major class of trigeminal neuropathic pain, dynamic mechanical allodynia (DMA), in a rat model of PD and in which a bilateral 6-hydroxy dopamine (6-OHDA) injection was administered to produce a lesion of the nigrostriatal dopaminergic pathway.

RESULTS AND DISCUSSION

Lesioned animals presented significant DMA in the orofacial area that occurred from 4 days to 5 weeks post-injury. To investigate a segmental implication in the neuropathic pain induced by dopamine depletion, the expression of the isoform gamma of the protein kinase C (PKCg) and phosphorylated extracellular signal-regulated kinases 1/2 (pERK1/2) was explored in the medullary dorsal horn (MDH). There was a high increase in PKCg expression in the III and IIi laminae of the MDH of lesioned-animals compared to shams. pERK1/2 expression was also significantly high in the ipsilateral MDH of lesioned rats in response to non-noxious tactile stimulus of the orofacial region. Since pERK1/2 is expressed only in response to nociceptive stimuli in the dorsal spinal horn, the current study demonstrates that non-noxious stimuli evoke allodynic response. Intraperitoneal and intracisternal administrations of bromocriptine, a dopamine 2 receptor (D2R) agonist, significantly decreased DMA compared to control rats injected with saline. These data demonstrate for the first time that nigrostriatal dopaminergic depletion produces trigeminal neuropathic pain that at least involves a segmental mechanism. In addition, bromocriptine was shown to have a remarkable analgesic effect on this neuropathic pain symptom.

Dopamine precursor depletion influences pain affect rather than pain sensation

Pain is a multidimensional experience, which includes sensory, cognitive, and affective aspects. Converging lines of evidence indicate that dopaminergic neurotransmission plays an important role in human pain perception. However, the precise effects of dopamine on different aspects of pain perception remain to be elucidated. To address this question, we experimentally decreased dopaminergic neurotransmission in 22 healthy human subjects using Acute Phenylalanine and Tyrosine Depletion (APTD). During APTD and a control condition we applied brief painful laser stimuli to the hand, assessed different aspects of pain perception, and recorded electroencephalographic responses. APTD-induced decreases of cerebral dopaminergic activity did not influence sensory aspects of pain perception. In contrast, APTD yielded increases of pain unpleasantness. The increases of unpleasantness ratings positively correlated with effectiveness of APTD. Our finding of an influence of dopaminergic neurotransmission on affective but not sensory aspects of phasic pain suggests that analgesic effects of dopamine might be mediated by indirect effects on pain affect rather than by direct effects on ascending nociceptive signals. These findings contribute to our understanding of the complex relationship between dopamine and pain perception, which may play a role in various clinical pain states.

Role of nucleus accumbens in neuropathic pain: linked multi-scale evidence in the rat transitioning to neuropathic pain

Despite recent evidence implicating the nucleus accumbens (NAc) as causally involved in the transition to chronic pain in humans, underlying mechanisms of this involvement remain entirely unknown. Here we elucidate mechanisms of NAc reorganizational properties (longitudinally and cross-sectionally), in an animal model of neuropathic pain (spared nerve injury [SNI]). We observed interrelated changes: (1) In resting-state functional magnetic resonance imaging (fMRI), functional connectivity of the NAc to dorsal striatum and cortex was reduced 28days (but not 5days) after SNI; (2) Contralateral to SNI injury, gene expression of NAc dopamine 1A, 2, and κ-opioid receptors decreased 28days after SNI; (3) In SNI (but not sham), covariance of gene expression was upregulated at 5days and settled to a new state at 28days; and (4) NAc functional connectivity correlated with dopamine receptor gene expression and with tactile allodynia. Moreover, interruption of NAc activity (via lidocaine infusion) reversibly alleviated neuropathic pain in SNI animals. Together, these results demonstrate macroscopic (fMRI) and molecular reorganization of NAc and indicate that NAc neuronal activity is necessary for full expression of neuropathic pain-like behavior.

Rotigotine transdermal system and evaluation of pain in patients with Parkinson's disease: a post hoc analysis of the RECOVER study

BACKGROUND

Pain is a troublesome non-motor symptom of Parkinson's disease (PD). The RECOVER (Randomized Evaluation of the 24-hour Coverage: Efficacy of Rotigotine; Clintrials.gov: NCT00474058) study demonstrated significant improvements in early-morning motor function (UPDRS III) and sleep disturbances (PDSS-2) with rotigotine transdermal system. Improvements were also reported on a Likert pain scale (measuring any type of pain). This post hoc analysis of RECOVER further evaluates the effect of rotigotine on pain, and whether improvements in pain may be attributable to benefits in motor function or sleep disturbance.

METHODS

PD patients with unsatisfactory early-morning motor impairment were randomized to optimal-dose (up to 16 mg/24 h) rotigotine or placebo, maintained for 4 weeks. Pain was assessed in the early-morning using an 11-point Likert pain scale (rated average severity of pain (of any type) over the preceding 12 hours from 0 [no pain] to 10 [worst pain ever experienced]). Post hoc analyses for patients reporting 'any' pain (pain score ≥1) at baseline, and subgroups reporting 'mild' (score 1-3), and 'moderate-to-severe' pain (score ≥4) were performed. Likert pain scale change from baseline in rotigotine-treated patients was further analyzed based on a UPDRS III/PDSS-2 responder analysis (a responder defined as showing a ≥30% reduction in early morning UPDRS III total score or PDSS-2 total score). As post hoc analyses, all p values presented are exploratory.

RESULTS

Of 267 patients with Likert pain data (178 rotigotine, 89 placebo), 187 (70%) reported 'any' pain; of these 87 (33%) reported 'mild', and 100 (37%) 'moderate-to-severe' pain. Change from baseline pain scores decreased with rotigotine compared with placebo in patients with 'any' pain (-0.88 [95% CI: -1.56, -0.19], p = 0.013), and in the subgroup with 'moderate-to-severe' pain (-1.38 [-2.44, -0.31], p = 0.012). UPDRS III or PDSS-2 responders showed greater improvement in pain than non-responders.

CONCLUSIONS

The results from this post hoc analysis of the RECOVER study suggest that pain was improved in patients with PD treated with rotigotine; this may be partly attributable to benefits in motor function and sleep disturbances. Prospective studies are warranted to investigate this potential benefit and the clinical relevance of these findings.

Sensory aspects of movement disorders

Movement disorders, which include disorders such as Parkinson's disease, dystonia, Tourette's syndrome, restless legs syndrome, and akathisia, have traditionally been considered to be disorders of impaired motor control resulting predominantly from dysfunction of the basal ganglia. This notion has been revised largely because of increasing recognition of associated behavioural, psychiatric, autonomic, and other non-motor symptoms. The sensory aspects of movement disorders include intrinsic sensory abnormalities and the effects of external sensory input on the underlying motor abnormality. The basal ganglia, cerebellum, thalamus, and their connections, coupled with altered sensory input, seem to play a key part in abnormal sensorimotor integration. However, more investigation into the phenomenology and physiological basis of sensory abnormalities, and about the role of the basal ganglia, cerebellum, and related structures in somatosensory processing, and its effect on motor control, is needed.

Pain in chemotherapy-induced neuropathy--more than neuropathic?

Chemotherapy-induced neuropathy (CIN) is an adverse effect of chemotherapy. Pain in CIN might comprise neuropathic and nonneuropathic (ie, musculoskeletal) pain components, which might be characterized by pain patterns, electrophysiology, and somatosensory profiling. Included were 146 patients (100 female, 46 male; aged 56 ± 0.8 years) with CIN arising from different chemotherapy regimens. Patients were characterized clinically through nerve conduction studies (NCS) and quantitative sensory testing (QST). Questionnaires for pain (McGill) and anxiety/depression (Hospital Anxiety and Depression Scale) were supplied. Patients were followed-up after 17 days. Large- (61%) and mixed- (35%) fibre neuropathies were more frequent than small-fibre neuropathy (1.4%). The 5 major chemotherapeutic regimens impacted differently on large- but not on small-fibre function and did not predict painfulness. Chronic pain associated with CIN was reported in 41.7%. Painless and painful CIN did not differ in QST profiles or electrophysiological findings, but different somatosensory patterns were found in CIN subgroups (pain at rest [RestP], n = 25; movement-associated pain [MovP], n = 15; both pain characteristics [MovP+RestP], n = 21; or no pain [NonP], n = 85): small-fibre function (cold-detection threshold, CDT: z score: -1.46 ± 0.21, P < 0.01) was most impaired in RestP; mechanical hyperalgesia was exclusively found in MovP (z score: +0.81 ± 0.30, P < 0.05). "Anxiety" discriminated between painful and painless CIN; "CDT" and "anxiety" discriminated between patients with ongoing (RestP) and movement-associated pain (MovP) or pain components (MovP+RestP). The detrimental effect of chemotherapy on large fibres failed to differentiate painful from painless CIN. Patients stratified for musculoskeletal or neuropathic pain, however, differed in psychological and somatosensory parameters. This stratification might allow for the application of a more specific therapy.