Influence of Dopaminergic Medication on Conditioned Pain Modulation in Parkinson's Disease Patients

TDCS for parkinson's disease disease-related pain: A randomized trial

OBJECTIVE

To evaluate the effects of transcranial direct current stimulation (tDCS) on Parkinson's disease (PD)-related pain.

METHODS

This triple-blind randomized controlled trial included twenty-two patients (age range 38-85, 10 male) with PD-related pain. Eleven subjects received ten sessions of 20 minutes tDCS over the primary motor cortex contralateral to pain at 2 mA intensity. Eleven subjects received sham stimulation. Outcome measures included changes in the Kinǵs Parkinsońs Pain Scale (KPPS), Brief Pain Inventory (BPI), widespread mechanical hyperalgesia (WMH), temporal summation of pain (TS), and conditioned pain modulation (CPM).

RESULTS

Significant differences were found in KPPS between groups favoring the active-tDCS group compared to the sham-tDCS group at 15-days follow-up (p = 0.014) but not at 2 days post-intervention (p = 0.059). The active-group showed significant improvements over the sham-group after 15 days (p = 0.017). Significant changes were found in CPM between groups in favor of active-tDCS group at 2 days post-intervention (p = 0.002) and at 15 days (p = 0.017). No meaningful differences were observed in BPI or TS.

CONCLUSIONS

tDCS of the primary motor cortex alleviates perceived PD-related pain, reduces pain sensitization, and enhances descending pain inhibition.

SIGNIFICANCE

This is the first study to test and demonstrate the use of tDCS for improving PD-related pain.

Pain in Parkinson disease: mechanistic substrates, main classification systems, and how to make sense out of them

ABSTRACT

Parkinson disease (PD) affects up to 2% of the general population older than 65 years and is a major cause of functional loss. Chronic pain is a common nonmotor symptom that affects up to 80% of patients with (Pw) PD both in prodromal phases and during the subsequent stages of the disease, negatively affecting patient's quality of life and function. Pain in PwPD is rather heterogeneous and may occur because of different mechanisms. Targeting motor symptoms by dopamine replacement or with neuromodulatory approaches may only partially control PD-related pain. Pain in general has been classified in PwPD according to the motor signs, pain dimensions, or pain subtypes. Recently, a new classification framework focusing on chronic pain was introduced to group different types of PD pains according to mechanistic descriptors: nociceptive, neuropathic, or neither nociceptive nor neuropathic. This is also in line with the International Classification of Disease-11 , which acknowledges the possibility of chronic secondary musculoskeletal or nociceptive pain due to disease of the CNS. In this narrative review and opinion article, a group of basic and clinical scientists revise the mechanism of pain in PD and the challenges faced when classifying it as a stepping stone to discuss an integrative view of the current classification approaches and how clinical practice can be influenced by them. Knowledge gaps to be tackled by coming classification and therapeutic efforts are presented, as well as a potential framework to address them in a patient-oriented manner.

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.

Chronic pain in Parkinson's disease: Clinical and pathophysiological aspects

Pain is an increasingly recognized non-motor symptom of Parkinson's disease (PD), with significant prevalence and strong impact on quality of life of patients. Moreover, pain can occur with various features in PD and several subtypes may coexist in a same patient, leading to a complex presentation and difficult diagnosis and treatment. In this paper we review the clinical manifestations of painful phenomena in PD, with focus on classifications and algorithms allowing to standardize the diagnosis of pain and PD. We also discuss the pathophysiological mechanisms underlying pain in PD, particularly parkinsonian central pain, in regard to recent clinical, neurophysiological and imaging studies.

Management of Pain in Parkinson's Disease

Pain is a very frequent symptom with influence on the quality of life in Parkinson’s disease (PD), but is still underdiagnosed and commonly treated only unsystematically. Pain etiology and pain character are often complex and multi-causal, and data regarding treatment recommendations are limited. Pain can be primarily related to PD but frequently it is associated with secondary diseases, such as arthrosis of the spine or joints. However, even basically PD-unrelated pain often is amplified by motor- or non-motor PD symptoms, such as akinesia or depression. Beyond an optimization of anti-parkinsonian treatment, additional pain treatment strategies are usually needed to properly address pain in PD. A careful pain history and diagnostic work-up is essential to rate the underlying pain pathophysiology and to develop a targeted therapeutic concept. This review gives an overview on how pain is treated in PD patients and how patients assess the effectiveness of these therapies; here, the manuscript focuses on pathophysiology-driven suggestions for a multimodal pain management in clinical practice.

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.

The challenge of pain in the pharmacological management of Parkinson's disease

Introduction: Pain is a common symptom in Parkinson's disease (PD), impairing quality of life. The clinical appearance and the underlying etiologies are diverse. Different subtypes of pain may occur, with musculoskeletal pain considered to be the most frequent. Often there is also a combination of different causes of pain. There is a lack of controlled studies addressing pain therapy in PD. Areas covered: In this review the authors analyzed the currently available data, taking into account the available publications in the databases, especially PubMed. The authors further provided their expert perspectives on the challenges of treating pain in PD patients. Expert opinion: There is both nociceptive and neuropathic pain and in patients with PD, some PD-related pain and some unrelated. Diagnosis requires a thorough and differentiated history and examination, and targeted diagnostics. Therapeutically, many drugs are used, but the data is unfortunately limited and not specific. Medications used include Parkinson-related, mainly dopaminergic drugs, as well as opioids and non-opioid analgetics, anticonvulsives, antidepressants, and more recently cannabinoids. Currently, therapy is performed nonspecifically, without taking into account the special requirements of PD. Unfortunately, in many cases, pain is resistant to these therapies. In the future, both diagnostic and therapeutic efforts should be made to address this issue.

An updated review on pathophysiology and management of burning mouth syndrome with endocrinological, psychological and neuropathic perspectives

Burning mouth syndrome (BMS) is a chronic oro-facial pain disorder of unknown cause. It is more common in peri- and post-menopausal women, and sex hormone dysregulation is believed to be an important causative factor. Psychosocial events often trigger or exacerbate symptoms, and persons with BMS appear to be predisposed towards anxiety and depression. Atrophy of small nerve fibres in the tongue epithelium has been reported, and potential neuropathic mechanisms for BMS are now widely investigated. Historically, BMS was thought to comprise endocrinological, psychosocial and neuropathic components. Neuroprotective steroids and glial cell line-derived neurotrophic factor family ligands may have pivotal roles in the peripheral mechanisms associated with atrophy of small nerve fibres. Denervation of chorda tympani nerve fibres that innervate fungiform buds leads to alternative trigeminal innervation, which results in dysgeusia and burning pain when eating hot foods. With regard to the central mechanism of BMS, depletion of neuroprotective steroids alters the brain network-related mood and pain modulation. Peripheral mechanistic studies support the use of topical clonazepam and capsaicin for the management of BMS, and some evidence supports the use of cognitive behavioural therapy. Hormone replacement therapy may address the causes of BMS, although adverse effects prevent its use as a first-line treatment. Selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) may have important benefits, and well-designed controlled studies are expected. Other treatment options to be investigated include brain stimulation and TSPO (translocator protein 18 kDa) ligands.

Pain Modulation: From Conditioned Pain Modulation to Placebo and Nocebo Effects in Experimental and Clinical Pain

Accumulating evidence reveal important applications of endogenous pain modulation assessment in healthy controls and in patients in clinical settings, as dysregulations in the balance of pain modulatory circuits may facilitate pain and promote chronification of pain. This article reviews data on pain modulation, focusing on the mechanisms and translational aspects of pain modulation from conditioned pain modulation (CPM) to placebo and nocebo effects in experimental and clinical pain. The specific roles of expectations, learning, neural and neurophysiological mechanisms of the central nervous system are briefly reviewed herein. The interaction between CPM and placebo systems in pain inhibitory pathways is highly relevant in the clinic and in randomized controlled trials yet remains to be clarified. Examples of clinical implications of CPM and its relationship to placebo and nocebo effects are provided. A greater understanding of the role of pain modulation in various pain states can help characterize the manifestation and development of chronic pain and assist in predicting the response to pain-relieving treatments. Placebo and nocebo effects, intrinsic to every treatment, can be used to develop personalized therapeutic approaches that improve clinical outcomes while limiting unwanted effects.

Somatosensory function is impaired in patients with idiopathic REM sleep behaviour disorder

BACKGROUND

Idiopathic REM sleep behaviour disorder (iRBD) has been recognised as a significant biomarker for developing a neurodegenerative alpha-synucleinopathy, which is why iRBD is considered to be a prodromal state for alpha-synucleinopathies including Parkinson's disease (PD). Many patients with PD suffer from complaints of pain and present impaired somatosensory function. We hypothesized that pain perception and somatosensory function could be altered already in a preclinical stage of PD including iRBD. Hence, the objective of this study was to investigate pain perception and somatosensory function in patients with iRBD.

METHODS

Quantitative sensory testing (QST), laser evoked potentials (LEPs), and conditioned pain modulation (CPM) testing were performed in 13 iRBD patients without any clinical signs of PD or narcolepsy (11 males, 2 females, mean age 65.2 years) and 15 gender- and age-matched healthy control subjects (12 males, 3 females, mean age 65.8 years).

RESULTS

Thermal detection thresholds were higher in the iRBD group compared with the control group (cold detection threshold (CDT) p = 0.020, thermal sensory limen (TSL) p = 0.001), indicating an impaired temperature sensation in iRBD patients. The N2/P2 LEPs amplitude was smaller in iRBD patients than controls, but not statistically significant (p = 0.053).

CONCLUSIONS

This study found an impaired somatosensory function in iRBD patients, suggesting that somatosensory impairment might be an early feature in the neurodegenerative process of PD.

Pain perception in Parkinson's disease: A systematic review and meta-analysis of experimental studies

While hyperalgesia (increased pain sensitivity) has been suggested to contribute to the increased prevalence of clinical pain in Parkinson's disease (PD), experimental research is equivocal and mechanisms are poorly understood. We conducted a meta-analysis of studies comparing PD patients to healthy controls (HCs) in their response to experimental pain stimuli. Articles were acquired through systematic searches of major databases from inception until 10/2016. Twenty-six studies met inclusion criteria, comprising 1292 participants (PD=739, HCs=553). Random effects meta-analysis of standardized mean differences (SMD) revealed lower pain threshold (indicating hyperalgesia) in PD patients during unmedicated OFF states (SMD=0.51) which was attenuated during dopamine-medicated ON states (SMD=0.23), but unaffected by age, PD duration or PD severity. Analysis of 6 studies employing suprathreshold stimulation paradigms indicated greater pain in PD patients, just failing to reach significance (SMD=0.30, p=0.06). These findings (a) support the existence of hyperalgesia in PD, which could contribute to the onset/intensity of clinical pain, and (b) implicate dopamine deficiency as a potential underlying mechanism, which may present opportunities for the development of novel analgesic strategies.