Compulsive use of dopamine replacement therapy in Parkinson's disease: reward systems gone awry?

Novelty seeking behaviour in Parkinson's disease

Novelty seeking can be a positive trait leading to creativity and innovation, but it is also related to increased risk of damaging addictive behaviour. We have assessed novelty seeking with a three armed bandit task, in which novel stimuli were occasionally introduced, replacing choice options from which the participants had been choosing. This allowed us to assess whether or not they would be prone to selecting novel stimuli. We tested 25 non impulsive patients with Parkinson's disease (PD) and 27 PD patients with impulsive compulsive behaviours (ICBs). Both patient groups were examined "on" and "off" dopaminergic medication in a counterbalanced order and their behaviour was compared with 24 healthy controls. We found that PD patients with ICBs were significantly more prone to choose novel options than either non impulsive PD patients or controls, regardless of medication status. Our findings suggest that attraction to novelty is a personality trait in all PD patients with ICBs which is independent of medication status.

Dopamine-induced nonmotor symptoms of Parkinson's disease

Nonmotor symptoms of Parkinson's disease (PD) may emerge secondary to the underlying pathogenesis of the disease, while others are recognized side effects of treatment. Inevitably, there is an overlap as the disease advances and patients require higher dosages and more complex medical regimens. The non-motor symptoms that emerge secondary to dopaminergic therapy encompass several domains, including neuropsychiatric, autonomic, and sleep. These are detailed in the paper. Neuropsychiatric complications include hallucinations and psychosis. In addition, compulsive behaviors, such as pathological gambling, hypersexuality, shopping, binge eating, and punding, have been shown to have a clear association with dopaminergic medications. Dopamine dysregulation syndrome (DDS) is a compulsive behavior that is typically viewed through the lens of addiction, with patients needing escalating dosages of dopamine replacement therapy. Treatment side effects on the autonomic system include nausea, orthostatic hypotension, and constipation. Sleep disturbances include fragmented sleep, nighttime sleep problems, daytime sleepiness, and sleep attacks. Recognizing the non-motor symptoms that can arise specifically from dopamine therapy is useful to help optimize treatment regimens for this complex disease.

Impulse control disorders in Parkinson's disease: clinical characteristics and implications

Impulse control disorders (ICDs), specifically those related to excessive gambling, eating, sex and shopping, have been observed in a subset of people with Parkinson's disease (PD). Although some initial case reports claimed that dopamine replacement therapies, particularly dopamine agonists, cause ICDs, more recent, larger and better controlled studies indicate a more complicated picture. While dopamine replacement therapy use is related to ICDs, other vulnerabilities, some related to PD and/or its treatment directly and others seemingly unrelated to PD, have also been associated with ICDs in PD. This suggests a complex etiology with multiple contributing factors. As ICDs occur in a sizable minority of PD patients and can be associated with significant distress and impairment, further investigation is needed to identify factors that can predict who may be more likely to develop ICDs. Clinical implications are discussed and topics for future research are offered.

Impulse control and related disorders in Parkinson's disease patients treated with bilateral subthalamic nucleus stimulation: a review

Recently, impulse control and related disorders including punding and the dopamine dysregulation syndrome (DDS) have been increasingly recognized in treated patients with Parkinson's disease (PD). Especially the impulse control disorders (ICD) such as pathological gambling, hypersexuality, compulsive eating and buying may have dramatic repercussions on family, personal and professional life. Drug replacement therapy (DRT) is believed to play an important role in the onset of these behavioral disturbances. Although deep brain stimulation (DBS) of the subthalamic nucleus (STN) might be a therapeutic option for those patients with DRT-related behavior, it may also induce ICD. So far, little is known about the relationship between STN DBS and impulse control and related disorders. Our aim was to review the current knowledge on this relationship in PD patients. The available studies showed that stimulation of the STN is associated with both favorable and negative outcome in terms of impulse control and related disorders. Preoperative disorders may resolve or improve after STN DBS, but these can also worsen or show no change at all. Moreover, STN DBS can also reveal or even induce ICD. Possible explanations for this variability are proposed and suggestions for clinical management are given.

Cue-induced striatal dopamine release in Parkinson's disease-associated impulsive-compulsive behaviours

Impulsive-compulsive behaviours are a significant source of morbidity for patients with Parkinson's disease receiving dopaminergic therapy. The development of these behaviours may reflect sensitization of the neural response to non-drug rewards, similar to that proposed for sensitization to drug rewards in addiction. Here, by using (11)C-raclopride positron emission tomography imaging, we investigated the effects of reward-related cues and L-dopa challenge in patients with Parkinson's disease with and without impulsive-compulsive behaviours on striatal levels of synaptic dopamine. Eighteen patients (11 with and seven without impulsive-compulsive behaviours) underwent three (11)C-raclopride positron emission tomography scans. The impulsive-compulsive behaviours included hypersexuality, binge eating, punding, compulsive use of dopamine replacement therapy, compulsive buying and pathological gambling, with eight patients exhibiting more than one impulsive-compulsive behaviour. There were no significant differences in baseline dopamine D2 receptor availability between the Parkinson's disease groups. No differences were found when comparing the percentage change of raclopride binding potential between the two Parkinson's disease groups following L-dopa challenge with neutral cues. The group with Parkinson's disease with impulsive-compulsive behaviours had a greater reduction of ventral striatum (11)C-raclopride binding potential following reward-related cue exposure, relative to neutral cue exposure, following L-dopa challenge (16.3% compared with 5.8% in Parkinson's disease controls, P = 0.016). The heightened response of striatal reward circuitry to heterogeneous reward-related visual cues among a group of patients with different impulsive-compulsive behaviours is consistent with a global sensitization to appetitive behaviours with dopaminergic therapy in vulnerable individuals. Our findings are relevant for the broader debate on the relation between impulsive-compulsive behaviours and addictions and may have important implications with regards to advertisement legislation in an effort to prevent the onset of behavioural addictions.

Impulse control disorders in patients with Parkinson's disease receiving dopamine replacement therapy: evidence and implications for the addictions field

AIMS

To describe the prevalence, phenomenology and correlates of 'impulse control disorders' (ICDs) in patients with Parkinson's disease (PD) treated with dopamine replacement therapy (DRT); to assess the strength of the evidence that DRT plays a contributory causal role in these disorders; and to highlight the implications of these disorders for research in the addiction field.

METHODS

PubMed and Web of Science databases were searched and the reference lists of papers examined.

RESULTS

The prevalence of ICDs in Parkinson's patients using DRT varied between 3.5% and 13.6%, depending on the severity and range of disorders assessed. PD patients with ICDs were: generally younger; had an earlier onset of PD; had a personal or family history of substance abuse or an ICD; and were more likely to be treated with dopamine receptor agonists (DA agonists) than levodopa (l-dopa). There is reasonable evidence that dopaminergic medications play a causal role in ICDs in that they occur at a higher rate in an otherwise low-risk population of adults, begin after initiation of DA agonist therapy and cease upon its discontinuation. A causal relationship is biologically plausible, but the role of other factors (such as concurrent mood disorders) remain to be clarified by better-controlled studies.

CONCLUSIONS

Impulse control disorders among patients with Parkinson's disease receiving dopamine replacement therapy may provide a unique opportunity for addiction researchers to study the neurobiology of impulsive forms of behaviour (such as problem gambling) that appear to be caused, in part, by the therapeutic use of dopamine receptor agonists.

Low frequency of bipolar disorder, dopamine dysregulation syndrome, and punding in Brazilian patients with Parkinson's disease

OBJECTIVE

To investigate the frequency of bipolar disorder, dopamine dysregulation syndrome and punding in Parkinson's disease patients from a Brazilian movement disorders clinic.

METHOD

One hundred patients underwent a comprehensive psychiatric examination composed of MINI-plus and specific questionnaires to investigate dopamine dysregulation syndrome and punding.

RESULTS

We identified, respectively, one and five Parkinson's disease patients with bipolar disorder type I and type II. All manic/hypomanic episodes occurred before Parkinson's disease onset. No patient was identified with dopamine dysregulation syndrome or punding.

CONCLUSION

The frequency of manic/hypomanic episodes seems to decrease with Parkinson's disease onset, and local environmental factors (e.g. drug availability) may be responsible for the low frequency of dopamine dysregulation syndrome and punding in Brazilian Parkinson's disease patients.

Efficacy, safety, and patient preference of monoamine oxidase B inhibitors in the treatment of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and the most treatable. Treatment of PD is symptomatic and generally focuses on the replacement or augmentation of levodopa. A number of options are available for treatment, both in monotherapy of early PD and to treat complications of advanced PD. This review focuses on rasagiline and selegiline, two medications that belong to a class of antiparkinsonian drugs called monoamine oxidase B (MAO-B) inhibitors. Topics covered in the review include mechanism of action, efficacy in early and advanced PD, effects on disability, the controversy regarding disease modification, safety, and patient preference for MAO-B inhibitors.

Building a neuroscience of pleasure and well-being

BACKGROUND: How is happiness generated via brain function in lucky individuals who have the good fortune to be happy? Conceptually, well-being or happiness has long been viewed as requiring at least two crucial ingredients: positive affect or pleasure (hedonia) and a sense of meaningfulness or engagement in life (eudaimonia). Science has recently made progress in relating hedonic pleasure to brain function, and so here we survey new insights into how brains generate the hedonic ingredient of sustained or frequent pleasure. We also briefly discuss how brains might connect hedonia states of pleasure to eudaimonia assessments of meaningfulness, and so create balanced states of positive well-being. RESULTS: Notable progress has been made in understanding brain bases of hedonic processing, producing insights into that brain systems that cause and/or code sensory pleasures. Progress has been facilitated by the recognition that hedonic brain mechanisms are largely shared between humans and other mammals, allowing application of conclusions from animal studies to a better understanding of human pleasures. In the past few years, evidence has also grown to indicate that for humans, brain mechanisms of higher abstract pleasures strongly overlap with more basic sensory pleasures. This overlap may provide a window into underlying brain circuitry that generates all pleasures, including even the hedonic quality of pervasive well-being that detaches from any particular sensation to apply to daily life in a more sustained or frequent fashion. CONCLUSIONS: Hedonic insights are applied to understanding human well-being here. Our strategy combines new findings on brain mediators that generate the pleasure of sensations with evidence that human brains use many of the same hedonic circuits from sensory pleasures to create the higher pleasures. This in turn may be linked to how hedonic systems interact with other brain systems relevant to self-understanding and the meaning components of eudaimonic happiness. Finally, we speculate a bit about how brains that generate hedonia states might link to eudaimonia assessments to create properly balanced states of positive well-being that approach true happiness.

Socio-demographic and clinical factors influencing the adherence to treatment in Parkinson's disease: the ADHESON study

BACKGROUND

Symptoms of Parkinson's disease (PD) are usually controlled by a continuous titration of medication and addition of multiple therapies over the course of the disease. Therapeutic complex schemes, polymedication, comorbidities and the number of medications required contribute to non-adherence.

METHODS

This cross-sectional survey was performed in 418 patients with PD on treatment with any antiparkinsonian medication. Patient adherence was assessed through physicians' subjective perception and the Morisky-Green test (MGT). Several social, demographic and clinical features were correlated through bivariate and multivariate analyses.

RESULTS

According to the physician's opinion 93.7%, and according to the MGT 60.4% of patients were adherent to parkinsonian therapy. The bivariate analysis showed greater adherence in patients with a high level of knowledge about the disease (62.8%), good clinical control (63.6%), a spouse or life partner (63%) and higher incomes (66%). Negative correlation with psychiatric symptoms was found. In relation to the MGT, the logistic regression model showed a negative correlation between cognitive deterioration and psychiatric pathology and adherence to therapy.

CONCLUSIONS

The physician's impression overestimated the compliance of patients when compared with an objective evaluation such as the MGT. Cognitive impairment and psychiatric symptoms are the clinical variables associated with a lower level of adherence.

Nonmotor symptoms in Parkinson’s disease: the dark side of the moon

Nonmotor symptoms may appear during the course of Parkinson’s disease, complicating the advanced phase in particular, but are also common in the premotor phase of Parkinson’s disease. The appearance of nonmotor manifestations represents a milestone, determining a worse prognosis and lower quality of life; however, they are often misdiagnosed and untreated. The spectrum of nonmotor symptoms encompasses mood disorders, psychosis, dementia, sleep disorders, impulse-control disorders and autonomic dysfunctions. This article describes these nonmotor symptoms and their management.

Dopamine agonist-induced substance addiction: the next piece of the puzzle

Traditional antiparkinson treatment strategies strive to balance the antiparkinson effects of dopaminergic drugs with the avoidance of motor response complications. Dopamine agonists have an established role in delaying the emergence of motor response complications or reducing motor "off" periods. The recent recognition of a range of "behavioural addictions" that are linked to dopamine agonist use has highlighted the role of dopamine in brain reward function and addiction disorders in general. Dopamine agonists have now even been linked occasionally to new substance addictions. The challenge now for the Parkinsonologist is to also balance the net benefits of using dopamine agonists for their motor effects with avoiding the harm from behavioural compulsions.

Altruistic punishment in patients with Parkinson's disease with and without impulsive behaviour

Punishing violators of social norms when there is personal cost is known as altruistic punishment. We tested patients with Parkinson's disease (PD) with and without impulsive-compulsive behaviours (ICBs) and matched control subjects, on and off their regular dopamine replacement therapy on a task, in which the patients decided whether or not to invest a sum of money with a trustee. The sum was then quadrupled and the trustee could decide whether or not to return a portion of the investment. Participants could punish the trustee after they were informed of the trustee's decision. We found that PD patients without ICBs on or off medication punished more often than controls, whereas PD patients with ICBs punished more than controls on medication, but similar to controls off medication. These results suggest a role for dopamine in altruistic punishment decisions in PD patients with impulsive compulsive behaviour.

Risk and learning in impulsive and nonimpulsive patients with Parkinson's disease

Relatively little is known about the interaction between behavioral changes, medication, and cognitive function in Parkinson's disease (PD). We examined working memory, learning and risk aversion in PD patients with and without impulsive or compulsive behavior (ICB) and compared the results with those in a group of age-matched control subjects. Parkinson patients with PD+ICB had poorer working memory performance than either controls or PD patients without ICB. PD+ICB patients also showed decreased learning from negative feedback and increased learning from positive feedback in off compared with on dopaminergic medication. This interaction between medication status and learning was the opposite of that found in the PD patients without a diagnosis of ICB. Finally, the PD group showed increased risk preference on medication relative to controls, and the subgroup of PD+ICB patients with pathological gambling were overall more risk prone than the PD group. Thus, medication status and an impulsive behavioral diagnosis differentially affect several behaviors in PD.

Intact reward learning but elevated delay discounting in Parkinson's disease patients with impulsive-compulsive spectrum behaviors

It has been postulated that impulsive-compulsive spectrum behaviors (ICBs) in Parkinson's disease (PD) reflect overvaluation of rewards, resulting from excessive dopaminergic transmission in the ventral striatum. However, as the ventral striatum is also strongly implicated in delay discounting, an alternative explanation would be that, similar to stimulant-dependent individuals, PD patients with ICBs impulsively discount future rewards. To test these hypotheses, we investigated whether 36 medicated PD patients with and without ICBs differed from controls on measures of stimulus-reinforcement learning and delay discounting. There was a clear double dissociation between reward learning and impulsivity in PD patients with and without ICBs. Although PD patients without ICBs were impaired at learning stimulus-reward associations for high-probability stimuli, PD patients with ICBs were able to learn such associations equally as well as controls. By contrast, PD patients with ICBs showed highly elevated delay discounting, whereas PD patients without ICBs did not differ from controls on this measure. These results contradict the hypothesis that ICBs in PD result from overvaluation of rewards. Instead, our data are more consistent with a model in which excessive dopaminergic transmission induces a strong preference for immediate over future rewards, driving maladaptive behavior in PD patients with ICBs.

Excessive hoarding in Parkinson's disease

Hoarding is seen in several psychiatric conditions, but has not been specifically assessed in Parkinson's disease (PD). This study investigates hoarding tendency amongst patients with PD, and its association with impulsive-compulsive spectrum behaviors (ICBs). We compare clinical features, measures of hoarding, impulse buying, self-control, obsessive-compulsive symptoms, depression, and anxiety in 39 patients with PD with ICBs (PD + ICB), 61 patients with PD without ICBs (PD - ICB), and 50 healthy controls. A much higher proportion of PD + ICB (27.8%) than PD - ICB (3.5%) were hoarders (P = 0.001). 6% of healthy controls were hoarders. Compulsive shoppers scored higher than other varieties of ICB on excessive acquisition measures. Hoarding correlated positively with impulsive buying, obsessive-compulsive symptoms, PD duration, and negatively with self-control measures. Using multivariate regression analyzes, the presence of ICBs and measures of impulsive buying were the only variables independently associated with hoarding in PD. The association of hoarding with other ICBs and low trait impulse control suggests that excessive hoarding is related to the spectrum of impulsive behaviors in PD.

[Behavioral disorders in Parkinson's disease: from pathophysiology to the mastery of dopaminergic treatment]

INTRODUCTION

Behavioral changes in Parkinson's disease are complex and their pathophysiology is not yet fully understood. The dopaminergic system seems to play a major role and most of the behavioral disorders in Parkinson's disease can be classified into either hypodopaminergic if related to the disease itself or hyperdopaminergic if related to dopaminergic treatment.

STATE OF THE ART

Subthalamic stimulation, which enables withdrawal of dopaminergic medication at an advanced stage in the disease, provides a model for the study of certain nonmotor, dopamine-sensitive symptoms. Such a study has shown that apathy, which is the most frequent behavioral problem in Parkinson's disease, is part of a much broader hypodopaminergic behavioral syndrome which also includes anxiety and depression. Nonmotor fluctuations--essential fluctuations in the patient's psychological state--are an expression of mesolimbic denervation, as shown in positron emission tomography. Drug-induced sensitization of the denervated mesolimbic system accounts for hyperdopaminergic behavioral problems that encompass impulse control disorders that can be alternatively classified as behavioral addictions. The association of impulse control disorders and addiction to the dopaminergic medication has been called dopamine dysregulation syndrome. While L-dopa is the most effective treatment for motor symptoms, dopamine agonists are more effective in improving the nonmotor levodopa-sensitive symptoms. On the other hand, L-dopa induces more motor complications and dopamine agonist more behavioral side effects. There is increasing data and awareness that patients' quality of life appears to be dictated by hypo- and hyperdopaminergic psychological symptoms stemming from mesolimbic denervation and dopaminergic treatment rather than by motor symptoms and motor complications related to nigrostriatal denervation and dopaminergic treatment.

PERSPECTIVES

Better management requires knowledge of the clinical syndromes of hyper- and hypodopaminergic behaviors and nonmotor fluctuations, a better understanding of their underlying mechanisms and the development of new evaluation tools for these nonmotor symptoms.

CONCLUSIONS

The neurologist who strives to gain mastery of dopaminergic treatment needs to fine tune the dosage of levodopa and dopamine agonists on an individual basis, depending on the presence of motor and nonmotor signs respectively.

Emotion, decision-making and substance dependence: a somatic-marker model of addiction

Similar to patients with orbitofrontal cortex lesions, substance dependent individuals (SDI) show signs of impairments in decision-making, characterised by a tendency to choose the immediate reward at the expense of severe negative future consequences. The somatic-marker hypothesis proposes that decision-making depends in many important ways on neural substrates that regulate homeostasis, emotion and feeling. According to this model, there should be a link between abnormalities in experiencing emotions in SDI, and their severe impairments in decision-making in real-life. Growing evidence from neuroscientific studies suggests that core aspects of substance addiction may be explained in terms of abnormal emotional guidance of decision-making. Behavioural studies have revealed emotional processing and decision-making deficits in SDI. Combined neuropsychological and physiological assessment has demonstrated that the poorer decision-making of SDI is associated with altered reactions to reward and punishing events. Imaging studies have shown that impaired decision-making in addiction is associated with abnormal functioning of a distributed neural network critical for the processing of emotional information, including the ventromedial cortex, the amygdala, the striatum, the anterior cingulate cortex, and the insular/somato-sensory cortices, as well as non-specific neurotransmitter systems that modulate activities of neural processes involved in decision-making. The aim of this paper is to review this growing evidence, and to examine the extent of which these studies support a somatic-marker model of addiction.

Insights into pathophysiology of punding reveal possible treatment strategies

Punding is a stereotyped behavior characterized by an intense fascination with a complex, excessive, nongoal oriented, repetitive activity. Men tend to repetitively tinker with technical equipment such as radio sets, clocks, watches and car engines, the parts of which may be analyzed, arranged, sorted and cataloged but rarely put back together. Women, in contrast, incessantly sort through their handbags, tidy continuously, brush their hair or polish their nails. Punders are normally aware of the inapposite and obtuse nature of the behavior; however, despite the consequent self-injury, they do not stop such behavior. The most common causes of punding are dopaminergic replacement therapy in patients affected by Parkinson's disease (PD) and cocaine and amphetamine use in addicts. The vast majority of information about punding comes from PD cases. A critical review of these cases shows that almost all afflicted patients (90%) were on treatment with drugs acting mainly on dopamine receptors D1 and D2, whereas only three cases were reported in association with selective D2 and D3 agonists. Epidemiological considerations and available data from animal models suggest that punding, drug-induced stereotypies, addiction and dyskinesias all share a common pathophysiological process. Punding may be related to plastic changes in the ventral and dorsal striatal structures, including the nucleus accumbens, and linked to psychomotor stimulation and reward mechanisms. Possible management guidelines are proposed.

Non-motor dopamine withdrawal syndrome after surgery for Parkinson's disease: predictors and underlying mesolimbic denervation

Apathy has been reported to occur after subthalamic nucleus stimulation, a treatment of motor complications in advanced Parkinson's disease. We carried out a prospective study of the occurrence of apathy and associated symptoms, predictors and mechanisms in the year following subthalamic stimulation. Dopamine agonist drugs were discontinued immediately after surgery and levodopa was markedly reduced within 2 weeks. Apathy and depression were assessed monthly, using the Starkstein apathy scale and the Beck Depression Inventory. Dopamine agonists were re-introduced if patients developed apathy or depression. Preoperative non-motor fluctuations were evaluated using the Ardouin Scale. Depression, apathy and anxiety were evaluated both on and off levodopa. Analysis of predictors of apathy was performed using a Cox proportional hazard model. Twelve patients who developed apathy and a control group of 13 patients who did not underwent [11C]-raclopride positron emission tomography scanning before and after oral intake of methylphenidate. In 63 patients with Parkinson's disease treated with subthalamic stimulation, dopaminergic treatment was decreased by 82% after surgery. Apathy occurred after a mean of 4.7 (3.3-8.2) months in 34 patients and was reversible in half of these by the 12-month follow-up. Seventeen patients developed transient depression after 5.7 (4.7-9.3) months and these fell into the apathy group with one single exception. At baseline, fluctuations in depression, apathy and anxiety scores were greater in the group with apathy. Fluctuations in apathy, depression and anxiety ratings during a baseline levodopa challenge were also significant predictors of postoperative apathy in univariate analysis, but not motor and cognitive states or the level of reduction of dopaminergic medication. The multivariate model identified non-motor fluctuations in everyday life and anxiety score during the baseline levodopa challenge as two independent significant predictors of postoperative apathy. Without methylphenidate, [11C]-raclopride binding potential values were greater in apathetic patients bilaterally in the orbitofrontal, dorsolateral prefrontal, posterior cingulate and temporal cortices, left striatum and right amygdala, reflecting greater dopamine D2/D3 receptor density and/or reduced synaptic dopamine level in these areas. The variations of [11C]-raclopride binding potential values induced by methylphenidate were greater in non-apathetic patients in the left orbitofrontal cortex, dorsolateral prefrontal cortex, thalamus and internal globus pallidus and bilaterally in the anterior and posterior cingulate cortices, consistent with a more important capacity to release dopamine. Non-motor fluctuations are related to mesolimbic dopaminergic denervation. Apathy, depression and anxiety can occur after surgery as a delayed dopamine withdrawal syndrome. A varying extent of mesolimbic dopaminergic denervation and differences in dopaminergic treatment largely determine mood, anxiety and motivation in patients with Parkinson's disease, contributing to different non-motor phenotypes.

Neurological considerations: autism and Parkinson's disease

Within the spectrum of disorders that manifest obsessive-compulsive (OC) features lies a sub-cluster of neurological conditions. Autism and Parkinson's disease (PD) are examples of two such neurological disorders that seem quite dissimilar on the surface. Yet, both conditions can include repetitive behaviors of a compulsive-impulsive nature. Furthermore, while autism and PD differ in other associated symptom domains that shape the course of each disorder, both disorders share some phenomenology in the core domain of repetitive behaviors and involve basal ganglia and frontal lobe dysfunction, similar to OC disorder (OCD). Accordingly, examination of the similarities and differences between autism and PD may provide insight into the pathophysiology and treatment of OC spectrum disorders. The current review focuses on the phenomenology, comorbidity, course of illness, family history, brain circuitry, and treatment of autism and PD, as they relate to OCD and OC spectrum disturbances.

Pharmacological modulation of subliminal learning in Parkinson's and Tourette's syndromes

Theories of instrumental learning aim to elucidate the mechanisms that integrate success and failure to improve future decisions. One computational solution consists of updating the value of choices in proportion to reward prediction errors, which are potentially encoded in dopamine signals. Accordingly, drugs that modulate dopamine transmission were shown to impact instrumental learning performance. However, whether these drugs act on conscious or subconscious learning processes remains unclear. To address this issue, we examined the effects of dopamine-related medications in a subliminal instrumental learning paradigm. To assess generality of dopamine implication, we tested both dopamine enhancers in Parkinson's disease (PD) and dopamine blockers in Tourette's syndrome (TS). During the task, patients had to learn from monetary outcomes the expected value of a risky choice. The different outcomes (rewards and punishments) were announced by visual cues, which were masked such that patients could not consciously perceive them. Boosting dopamine transmission in PD patients improved reward learning but worsened punishment avoidance. Conversely, blocking dopamine transmission in TS patients favored punishment avoidance but impaired reward seeking. These results thus extend previous findings in PD to subliminal situations and to another pathological condition, TS. More generally, they suggest that pharmacological manipulation of dopamine transmission can subconsciously drive us to either get more rewards or avoid more punishments.

Nonmotor fluctuations in Parkinson's disease: clinical spectrum and classification

The majority of patients with Parkinson's disease (PD) on levodopa (LD) treatment usually experience motor fluctuations (MFs) within several years of initiation of treatment. Besides the classic MFs, many nonmotor fluctuations (NMFs) may occur in PD. NMFs appear both in the "on" state and "off" state. However, the clinical spectrum and the frequency of these symptoms are not well recognized. NMFs are usually mild and less disabling than MFs but sometimes can lead to unnecessary tests and therapies. NMFs occurring in association with the "on" state are better known and therefore more frequently diagnosed than those occurring in the "off" state. NMFs can be classified into three groups: autonomic, cognitive/psychiatric, and sensory. They include gastrointestinal and urinary symptoms, drenching sweats, temperature and blood-pressure changes, depression, anxiety, hallucinations, hypomania, moaning/screaming, confusion, cognitive dysfunction, sexual deviations and dopamine dysregulation syndrome (DDS), pain, akathisia, internal tremor, numbness/parasthesia, and dyspnea.

CONCLUSION

Recognition of NMFs may prevent unnecessary diagnostic tests and may lead to treatment modifications aimed to minimize their occurrence.

Dopamine dysregulation syndrome and levodopa-induced dyskinesias in Parkinson disease: common consequences of anomalous forms of neural plasticity

Four to 10% of patients with Parkinson disease and chronically treated with levodopa undergo an addictionlike behavioral disturbance named dopamine dysregulation syndrome (DDS). This article suggests that patients with Parkinson disease could be especially prone to develop DDS due to the dopamine deficiency and the "priming" of neural networks by the chronic use of drugs with a short half-life, such as levodopa. These suggestions are based on the clinical and molecular similarities between levodopa-induced dyskinesias and behavioral alterations seen in DDS and addiction to illegal drugs. Motor and behavioral abnormalities can be seen as the consequence of common mechanisms involving anomalous forms of neural plasticity. These forms affect parts of the cortical-basal ganglia-thalamocortical circuits that are topographically organized to differently modulate emotional and motor functions. Recent evidence using positron emission tomography provides support to this idea. By contrast, molecular data suggest that functional segregation may be lost in addiction, DDS, and dyskinesias. The existence of common pathogenic mechanisms for both phenomena could provide the basis for common therapeutic strategies.

Behavioural adverse effects of dopaminergic treatments in Parkinson's disease: incidence, neurobiological basis, management and prevention

Treatment of Parkinson's disease has traditionally focused on the management of motor disability while behavioural disturbances have received less attention. Recently, impulse control disorders and aberrant repetitive behaviours have surged to clinical relevance as they occur during dopamine replacement treatment (mainly with dopamine agonists) and worsen patient and caregiver quality of life. Patients are unable to adequately estimate the negative consequences of their actions and are prone to entertain compulsive reward-seeking activities. This review aims to summarize current evidence on the epidemiology of behavioural disturbances in Parkinson's disease, recent insights into their neurobiological basis and to discuss strategies for management and prevention. Studies from 1990 through to December 2008 were retrieved via searches of the Cochrane Database of Systematic Reviews and PubMed. The mechanisms underlying the development of behavioural disturbances in Parkinson's disease are debated but current evidence points to specific risk factors: male sex, young age at onset, underlying personality traits characterized by high impulsivity and novelty seeking, and personal or family history of addictive disorders. Specifically, in predisposed individuals dopamine replacement therapy leads to overstimulation of dopamine receptors within the mesocorticolimbic pathways and in turn to the development of addictive behaviours, such as impulse control disorders and compulsive medication intake. Since these disturbances affect individuals who have often unremarkable psychiatric history and no cognitive impairment, their identification and management is complex. Compulsive medication intake (described as 'hedonistic homeostatic dysregulation' or 'dopamine dysregulation syndrome') is commonly associated with fluctuations in advanced disease, while impulse control disorders frequently occur in early Parkinson's disease and within normal-range medication dosages. Management primarily requires reduction of dopaminergic therapy but psychosocial support is often required. Use of selective serotonin reuptake inhibitors in the dose used for obsessive compulsive disorders may help, while benefit from atypical antipsychotics is limited in most cases. Deep brain stimulation should be considered with caution in these subjects. Prevention is based on the identification of at-risk individuals and active monitoring. Given the social and potentially medical-legal consequences of these behaviours, we encourage treating physicians to discuss risks with patients before treatment is initiated.

Adherence to antiparkinson medication in a multicenter European study

Two small studies reported suboptimal therapy adherence in Parkinson's disease. We conducted a larger multicenter European study to assess medicine-taking behavior. Parkinson's disease patients taking dopaminergic therapy were enrolled in 8 centers in 5 countries, and disease severity and demographics recorded. Antiparkinson drug adherence was measured for 4 weeks using electronic monitoring bottles which record the date and time of cap opening (Aardex, Switzerland). One hundred twelve patients, mean age 65 years (standard deviation (SD) 10), with Parkinson's disease for 7.7 (SD 8.2) years completed the study. Total median adherence (doses taken/doses prescribed) was 97.7% (interquartile range [IQ] 90.6-100), days adherence (correct dose days) was 86.2% (IQ 61.1-96.2) and timing adherence (doses taken at correct time intervals) was 24.4% (IQ 5.3-56.5). Fourteen patients (12.5%) took less than 80% of prescribed doses, which was defined as suboptimal adherence. Patients with satisfactory adherence took a median of 8 mg/day (IQ 0-33) less than their prescribed dose of levodopa (P = NS), while suboptimal adherence patients took a median of 481 mg/day (IQ 205-670) less than their prescribed dose (P = 0.0006). The Parkinson motor score was significantly higher in patients with suboptimal adherence at 29 (IQ 20-40), versus those with satisfactory adherence at 19 (IQ 13-26), P = 0.005. Once daily drugs had significantly better adherence when compared with drugs prescribed more frequently (P < 0.0001). Suboptimal therapy adherence is associated with significant deviation from prescribed levodopa doses, despite greater Parkinson's motor severity. Optimizing oral medication intake has a potential role in maximizing the therapy response in Parkinson's disease.

Dopamine dysregulation syndrome in a patient with restless legs syndrome

A middle-aged architect, suffering from familial, idiopathic, levodopa-responsive restless legs syndrome (RLS) progressively abused levodopa for 10 years, to the point of taking 20 tablets/day (4000 mg/day) for 6 months. Such abuse (possibly linked to the rewarding effect of dopamine) has been recently monitored in the context of Parkinson's disease (PD) (the "dopamine dysregulation syndrome"). Physicians who now routinely treat RLS patients with dopaminergic agents should be aware of this abuse potential. This case also constitutes an experimental model. As levodopa abuse has only been described in patients with PD, it was suspected to be promoted by central dopamine depletion (with consequent sensitization of dopamine receptors). This idea should be revised because functional imaging showed that this RLS patient had no dopamine depletion. Later, he had no impulse disorders (no gambling, hypersexuality, excessive shopping), which occur with dopamine agonists, suggesting that levodopa abuse and impulse disorders can result through different mechanisms.

On the role of dopamine replacement therapy in decision-making, working memory, and reward in Parkinson's disease: does the therapy-dose matter?

BACKGROUND

Dopaminergic therapy proved to ameliorate motor deficits in Parkinson's disease but its effects on behavior and cognition vary according to factors that include, among others, the evolution of the disease and the nature of the task that is tested. This study addressed the question of whether, in moderate to advanced Parkinson's disease (PD) with motor fluctuations, changes in decision-making and sensitivity to reward occur and to what extent dopaminergic therapy plays a role.

METHODS

Fifteen PD patients (On and Off medication) and thirteen healthy controls were compared on two different tasks which analyzed decision-making processes (the Cambridge Gamble Task, CGT) and working memory abilities with and without the prospect of reward (modified N-back task).

RESULTS

We found that the PD patients were unable to choose an optimal betting strategy and were impulsive in their choices relative to the control group. Further, a detrimental dose-dependent effect of dopaminergic therapy was detected, meaning that those patients who were taking higher doses of therapy were more impulsive in selecting bets and more impaired in making probabilistic choices. Such a dose-dependent effect was not found on the N-back task. However, the results of the PD group in this task supported indirect evidence of the amelioration of performance in rewarded conditions.

CONCLUSION

Our results suggest that the detrimental effects of dopaminergic therapy may be dose-related and that the interaction between monetary reward and dopaminergic therapy can affect and improve some cognitive abilities, such as working memory.

Dopamine dysregulation syndrome: an overview of its epidemiology, mechanisms and management

Dopamine dysregulation syndrome (DDS) is a relatively recently described iatrogenic disturbance that may complicate long-term symptomatic therapy of Parkinson's disease. Patients with DDS develop an addictive pattern of dopamine replacement therapy (DRT) use, administering doses in excess of those required to control their motor symptoms. The prevalence of DDS in patients attending specialist Parkinson's disease centres is 3-4%. Amongst the behavioural disturbances associated with DDS are punding, which is a complex stereotyped behaviour, and impulse control disorders (ICDs), such as pathological gambling, hypersexuality, compulsive shopping and compulsive eating. We review the risk factors and potential mechanisms for the development of DDS, including personality traits, potential genetic influences and Parkinson's disease-related cognitive deficits. Impulsive personality traits are prominent in patients developing DDS, and have been previously associated with the development of substance dependence. Candidate genes affecting the dopamine 'D(2)-like' receptor family have been associated with impulsive personality traits in addition to drug and nondrug addictions. Impaired decision making is implicated in addictive behaviours, and decision-making abilities can be influenced by dopaminergic medications. In Parkinson's disease, disruption of the reciprocal loops between the striatum and structures in the prefrontal cortex following dopamine depletion may predispose to DDS. The role of DRT in DDS is discussed, with particular reference to models of addiction, suggesting that compulsive drug use is due to progressive neuroadaptations in dopamine projections to the accumbens-related circuitry. Evidence for neuroadaptations and sensitization occurring in DDS include enhanced levodopa-induced ventral striatal dopamine release. Levodopa is still considered the most potent trigger for DDS in Parkinson's disease, but subcutaneous apomorphine and oral dopamine agonists may also be responsible. In the management of DDS, further research is needed to identify at-risk groups, thereby facilitating more effective early intervention. Therefore, an increased awareness of the syndrome amongst treating physicians is vital. Medication reduction strategies are employed, particularly with regard to avoiding rapidly acting 'booster' DRT formulations. Psychosocial treatments, including cognitive-behavioural therapy, have been beneficial in treating substance use disorders and ICDs in non-Parkinson's disease patients, but there are currently no published trials of psychological interventions in DDS. Further studies are also required to identify factors that can predict those patients with DDS or ICDs who will derive benefit from surgical interventions such as deep brain stimulation.

Increased striatal dopamine release in Parkinsonian patients with pathological gambling: a [11C] raclopride PET study

Pathological gambling is an impulse control disorder reported in association with dopamine agonists used to treat Parkinson's disease. Although impulse control disorders are conceptualized as lying within the spectrum of addictions, little neurobiological evidence exists to support this belief. Functional imaging studies have consistently demonstrated abnormalities of dopaminergic function in patients with drug addictions, but to date no study has specifically evaluated dopaminergic function in Parkinson's disease patients with impulse control disorders. We describe results of a [(11)C] raclopride positron emission tomography (PET) study comparing dopaminergic function during gambling in Parkinson's disease patients, with and without pathological gambling, following dopamine agonists. Patients with pathological gambling demonstrated greater decreases in binding potential in the ventral striatum during gambling (13.9%) than control patients (8.1%), likely reflecting greater dopaminergic release. Ventral striatal bindings at baseline during control task were also lower in patients with pathological gambling. Although prior imaging studies suggest that abnormality in dopaminergic binding and dopamine release may be markers of vulnerability to addiction, this study presents the first evidence of these phenomena in pathological gambling. The emergence of pathological gambling in a number of Parkinson's disease patients may provide a model into the pathophysiology of this disorder.

Parkinson's disease-related disorders in the impulsive-compulsive spectrum

In Parkinson's disease (PD), there is increasing evidence for disorders in the impulsive-compulsive spectrum, related to the disease itself, to the pharmacological management of this disease or to both. These disorders comprise dopamine deficiency syndrome (with immediate reward seeking behaviour), dopamine dependency syndrome (with addictive behaviour), dopamine dysregulation syndrome (with both addictive behaviour and stereotyped behaviour) and impulse control disorders (such as pathological gambling, compulsive shopping, binge eating and hypersexuality). These disorders are especially seen in PD patients with young age of onset, higher doses of antiparkinsonian drugs, pre-existent or current depression, pre-existing recreational drug or alcohol use, and high novelty seeking personality traits.Dopamine is not only implicated in voluntary movement control but also plays a significant role in the brain's reward system and the modulation of behaviours. Therefore, most if not all drugnaïve PD patients will suffer dysphoria, leading to mild immediate reward seeking behaviour as a consequence of the striatal dopaminergic denervation. In some of these patients, during treatment, this may even lead to the intake of increasing quantities of levodopa, above those required to adequately treat motor parkinsonism, with all characteristics of a dopamine dependence syndrome. These patients may develop plastic changes in the striatal matrix leading to hyperkinesia, caused by extracellular striatal dopaminergic fluctuations due to pulsatile dopamine replacement therapy. As soon as these changes are also seen in the striatal striosomes, in the framework of a dopamine dysregulation syndrome, stereotyped behaviours (punding) may occur (supposedly due to dorsal versus ventral striatal overactivity). Finally, impulse control disorders are suggested as being pure adverse side-effects of dopamine replacement therapy. Obsessive-compulsive behaviour (caused by ventral to dorsal overactivity) so far has not been described in PD patients.Treatment of impulse control disorders is related to the underlying pathology. In the case of an intrinsic dopamine deficiency syndrome, treatment with dopamine replacement therapy, especially levodopa, will help. In the multifactorial (intrinsic and extrinsic) dopamine dependency and dysregulation syndromes, addictive behaviour might best be helped by psychosocial strategies, and punding by continuous dopaminergic receptor stimulation (or amantadine), hypothesized to reduce the plastic changes-induced hypersensitization. The extrinsic impulse control disorders might be best treated by reducing or replacing dopamine receptor agonists.