Impulse control disorders (ICDs), including disordered gambling, can occur in a significant number of patients with Parkinson’s disease (PD) receiving dopaminergic therapy. The neurobiology underlying susceptibility to such problems is unclear, but risk likely results from an interaction between dopaminergic medication and a pre-existing trait vulnerability. Impulse control and addictive disorders form part of a broader psychopathological spectrum of disorders, which share a common underlying genetic vulnerability, referred to as externalizing. The broad externalizing risk factor is a continuously varying trait reflecting vulnerability to various impulse control problems, manifested at the overt level by disinhibitory symptoms and at the personality level by antecedent traits such as impulsivity and novelty/sensation seeking. Trait “disinhibition” is thus a core endophenotype of ICDs, and a key target for neurobiological investigation. The ventral striatal dopamine system has been hypothesized to underlie individual variation in behavioral disinhibition. Here, we examined whether individual differences in ventral striatal dopamine synthesis capacity predicted individual variation in disinhibitory temperament traits in individuals with PD. Eighteen early-stage male PD patients underwent 6-[18F]Fluoro-l-DOPA (FDOPA) positron emission tomography scanning to measure striatal dopamine synthesis capacity, and completed a measure of disinhibited personality. Consistent with our predictions, we found that levels of ventral, but not dorsal, striatal dopamine synthesis capacity predicted disinhibited personality, particularly a propensity for financial extravagance. Our results are consistent with recent preclinical models of vulnerability to behavioral disinhibition and addiction proneness, and provide novel insights into the neurobiology of potential vulnerability to impulse control problems in PD and other disorders.
dopa decarboxylase; dopamine; disordered gambling; externalizing; impulse control disorders; impulsivity; reward; ventral striatum
Impulse control disorders are a psychiatric condition characterized by the failure to resist an impulsive act or behavior that may be harmful to self or others. In movement disorders, impulse control disorders are associated with dopaminergic treatment, notably dopamine agonists (DAs). Impulse control disorders have been studied extensively in Parkinson’s disease, but are also recognized in restless leg syndrome and atypical Parkinsonian syndromes. Epidemiological studies suggest younger age, male sex, greater novelty seeking, impulsivity, depression and premorbid impulse control disorders as the most consistent risk factors. Such patients may warrant special monitoring after starting treatment with a DA. Various individual screening tools are available for people without Parkinson’s disease. The Questionnaire for Impulsive-Compulsive Disorders in Parkinson’s Disease has been developed specifically for Parkinson’s disease. The best treatment for impulse control disorders is prevention. However, after the development of impulse control disorders, the mainstay intervention is to reduce or discontinue the offending anti-Parkinsonian medication. In refractory cases, other pharmacological interventions are available, including neuroleptics, antiepileptics, amantadine, antiandrogens, lithium and opioid antagonists. Unfortunately, their use is only supported by case reports, small case series or open-label clinical studies. Prospective, controlled studies are warranted. Ongoing investigations include naltrexone and nicotine.
Impulse control disorders; Parkinson’s disease; restless leg syndrome; parkinsonism; dopamine agonist; non-motor complication; neurobehavioural
The development of an impulse control disorder (ICD) is now recognized as a potential nonmotor adverse effect of dopamine replacement therapy in Parkinson’s disease (PD). Here, recent epidemiological, neurophysiological and genetic advances are summarized to outline potential mechanisms involved. It is safe to say that dopaminergic drugs, particularly dopamine agonists, are able to induce ICDs only in a minority of patients, while the majority are somehow protected from this adverse effect. While it seems clear that men with early-onset PD are more vulnerable, other predisposing factors, such as various current or pre-PD personality traits, are a matter of debate. In terms of neurophysiological advances, one may find striking analogies to the addiction literature suggesting a causal chain beginning with certain predisposing conditions of striatal dopamine synapses, an “unnatural” increase of dopamine stimulation and a characteristic pattern of resulting functional changes in remote networks of appetitive drive and impulse control. Future prospects include potential add-on medications and the possible identification of genetic predispositions at a genome-wide scale. Functional imaging of pharmacogenetic interactions (imaging pharmacogenomics) may be an important tool on that road.
Imaging; Gambling; Addiction; Impulsive; Compulsive; Dopamine agonist
To review the neurobiological substrates of impulse control disorders (ICDs). Pathological gambling (PG) is a main focus of the review in that most biological studies of the formal ICDs have examined this disorder.
The medical database MedLine from 1966 to present was searched to identify relevant articles that were subsequently reviewed to generate this manuscript.
Preclinical studies suggest that differential brain monoamine neuromodulation is associated with impulsive decision-making and risk-taking behaviors. Clinical studies implicate multiple neurotransmitter systems (serotonergic, dopaminergic, adrenergic, and opioidergic) in the pathophysiology of PG and other ICDs. Initial neuroimaging studies have implicated the ventromedial prefrontal cortex and ventral striatum in the pathophysiology of PG and other ICDs. Genetic contributions to PG seem substantial and initial studies have implicated specific allelic polymorphisms, although genome-wide analyses have yet to be published.
Although significant advances have been made in our understanding of the neurobiology of ICDs, more research is needed to extend existing knowledge and translate these findings into clinical advances.
Pathological Gambling; Serotonin; Norepinephrine; Dopamine; Opioids; Impulsivity; Stress; Genetics; Brain Imaging; Biochemistry
Parkinson's disease (PD) has been associated with the development of impulse control disorders (ICDs), possibly due to overstimulation of the mesolimbic system by dopaminergic medication. Preliminary reports have suggested that deep brain stimulation (DBS), a neurosurgical procedure offered to patients with treatment-resistant PD, affects ICD in a twofold way. Firstly, DBS allows a decrease in dopaminergic medication and hence causes an improvement in ICDs. Secondly, some studies have proposed that specific ICDs may develop after DBS. This paper addresses the effects of DBS on ICDs in patients with PD. A
literature search identified four original studies examining a total of 182 patients for ICDs and nine case reports of 39 patients that underwent DBS and developed ICDs at some point. Data analysis from the original studies did not identify a significant difference in ICDs between patients receiving dopaminergic medication and patients on DBS, whilst the case reports showed that 56% of patients undergoing DBS had poor outcome with regards to ICDs. We discuss these ambivalent findings in the light of proposed pathogenetic mechanisms. Longitudinal, prospective studies with larger number of patients are required in order to fully understand the role of DBS on ICDs in patients with PD.
The article reviews the current knowledge about the impulse control disorders (ICDs) with specific emphasis on epidemiological and pharmacological advances. In addition to the traditional ICDs present in the DSM-IV—pathological gambling, trichotillomania, kleptomania, pyromania and intermittent explosive disorder—a brief description of the new proposed ICDs—compulsive–impulsive (C–I) Internet usage disorder, C–I sexual behaviors, C–I skin picking and C–I shopping—is provided. Specifically, the article summarizes the phenomenology, epidemiology and comorbidity of the ICDs. Particular attention is paid to the relationship between ICDs and obsessive–compulsive disorder (OCD). Finally, current pharmacological options for treating ICDs are presented and discussed.
impulse control disorders (ICDs); obsessive–compulsive disorder (OCD); pathological gambling (PG); kleptomania; compulsive–impulsive (C–I) shopping; trichotillomania (TTM); intermittent explosive disorder (IED); C–I Internet usage disorder; C–I sexual behaviors (C–ISBs); C–I skin picking; pyromania
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 disorders (ICDs) and apathy are recognized as two important neuropsychiatric syndromes associated with Parkinson’s disease (PD), but as yet we understand very little about the cognitive mechanisms underlying them. Here, we review emerging findings, from both human and animal studies, that suggest that impulsivity and apathy are opposite extremes of a dopamine-dependent spectrum of motivated decision making. We first argue that there is strong support for a hypodopaminergic state in PD patients with apathy, as well as for an association between dopamine therapy and development of ICDs. However, there is little evidence for a clear dose-response relationship, and great heterogeneity of findings. We argue that dopaminergic state on its own is an insufficient explanation, and suggest instead that there is now substantial evidence that both apathy and impulsivity are in fact multi-dimensional syndromes, with separate, dissociable mechanisms underlying their ‘surface’ manifestations. Some of these mechanisms might be dopamine-dependent. According to this view, individuals diagnosed as impulsive or apathetic may have very different mechanisms underlying their clinical states. We propose that impulsivity and apathy can arise from dissociable deficits in option generation, option selection, action initiation or inhibition and learning. Review of the behavioural and neurobiological evidence leads us to a new conceptual framework that might help understand the variety of functional deficits seen in PD.
Impulsive personalities are considered to have a general impairment in cognitive flexibility and cortical inhibition. To examine this hypothesis we used a trial by trial Stroop task in impulsive and non impulsive patients with Parkinson’s disease (PD) and recorded errors and reaction times (RT). We tested 28 impulsive PD (PD+ICB) and 24 non impulsive PD (PD-ICB) patients prior to and after dopaminergic medication. These results were compared with 24 age matched normal controls. We found an increased error rate in all PD patients prior to their usual medication which resolved after medication. Furthermore patients on medication showed enhanced cognitive flexibility and shorter RT. There was no difference between non impulsive and impulsive PD patients. This suggests that the impulsive behaviours may not affect response inhibition tasks and the response inhibition required in the Stroop test does not engage the same processes that differentiate impulsive and non-impulsive PD patients, which likely involve mesolimbic dopamine.
Recent studies have linked dopamine agonist (DA) usage with the development of impulse control disorders (ICDs) in Parkinson’s disease (PD). Little is known about optimal management strategies or the long-term outcomes of affected patients. To report on the clinical interventions and long-term outcomes of PD patients who developed an ICD after DA initiation. Subjects contacted by telephone for a follow-up interview after a mean time period of 29.2 months. They were administered a modified Minnesota Impulse Disorder Interview for compulsive buying, gambling, and sexuality, and also self-rated changes in their ICD symptomatology. Baseline and follow-up dopamine replacement therapy use was recorded and verified by chart review. Of 18 subjects, 15 (83.3%) participated in the follow-up interview. At follow-up, patients were receiving a significantly lower DA levodopa equivalent daily dosage (LEDD) (Z = -3.1, P = 0.002) and a higher daily levodopa dosage (Z = -1.9, P = 0.05), but a similar total LEDD dosage (Z = -0.47, P = 0.64) with no changes in Unified Parkinson’s Disease Rating Scale motor score (Z = -1.3, P = 0.19). As part of ICD management, 12 (80.0%) patients discontinued or significantly decreased DA treatment, all of whom experienced full or partial remission of ICD symptoms by self-report, and 10 (83.3%) of whom no longer met diagnostic criteria for an ICD. For PD patients who develop an ICD in the context of DA treatment, discontinuing or significantly decreasing DA exposure, even when offset by an increase in levodopa treatment, is associated with remission of or significant reduction in ICD behaviors without worsening in motor symptoms.
dopamine agonist; gambling; impulse control disorders; Parkinson’s disease
Impulse control disorders (ICDs) and dopamine dysregulation syndrome (DDS) are important behavioral problems that affect a subpopulation of patients with Parkinson's disease (PD) and typically result in markedly diminished quality of life for patients and their caregivers. We aimed to investigate the effects of subthalamic nucleus (STN) and internal globus pallidus (GPi) deep brain stimulation (DBS) on ICD/DDS frequency and dopaminergic medication usage.
A retrospective chart review was performed on 159 individuals who underwent unilateral or bilateral PD DBS surgery in either STN or GPi. According to published criteria, pre- and post-operative records were reviewed to categorize patients both pre- and post-operatively as having ICD, DDS, both ICD and DDS, or neither ICD nor DDS. Group differences in patient demographics, clinical presentations, levodopa equivalent dose (LED), and change in diagnosis following unilateral/bilateral by brain target (STN or GPi DBS placement) were examined.
28 patients met diagnostic criteria for ICD or DDS pre- or post-operatively. ICD or DDS classification did not differ by GPi or STN target stimulation. There was no change in DDS diagnosis after unilateral or bilateral stimulation. For ICD, diagnosis resolved in 2 of 7 individuals after unilateral or bilateral DBS. Post-operative development of these syndromes was significant; 17 patients developed ICD diagnoses post-operatively with 2 patients with pre-operative ICD developing DDS post-operatively.
Unilateral or bilateral DBS did not significantly treat DDS or ICD in our sample, even though a few cases of ICD resolved post-operatively. Rather, our study provides preliminary evidence that DDS and ICD diagnoses may emerge following DBS surgery.
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 (ICB). 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.
To determine the frequency and correlates of impulse control disorders (ICDs) in Parkinson’s disease (PD).
An unstructured screening interview for ICDs (compulsive gambling, buying, and sexual behavior) followed by a telephone-administered structured interview for screen-positive patients.
Two university-affiliated movement disorders centers.
A convenience sample of 272 patients with idiopathic PD who were screened for psychiatric complications.
Main Outcome Measures
Presence of compulsive gambling, buying, or sexual behavior as assessed by the Minnesota Impulsive Disorders Interview.
Eighteen (6.6%) PD patients met criteria for an ICD at some point during the course of PD, including 11 (4.0%) with an active ICD. Compulsive gambling and compulsive sexual behavior were equally common. In a multivariate model, treatment with a dopamine agonist (P = .01) and a history of ICD symptomatology prior to PD onset (P = .02) predicted current ICD. There were no differences between the dopamine agonists in their association with ICDs (P = .21), and daily doses of dopamine agonists were higher in patients with an ICD than in dopamine agonist-treated patients without an ICD (P < .001).
PD patients treated with a dopamine agonist should be made aware of the risk of developing an ICD and monitored clinically. As dopamine agonists are increasing being used for other indications, future research should assess the dopamine agonist-associated risk for ICDs in other populations.
Given that impulse control disorders (ICDs) have been identified among a considerable minority of Parkinson's disease (PD) patients, these conditions have gained increased clinical and research attention in the past decade. Dopamine-replacement therapies, taken to ameliorate PD symptoms, have been associated with ICDs in PD. Unfortunately, there are relatively sparse empirical data regarding how best to address ICDs in PD patients. Conversely, progress has been made in understanding the clinical, neurobiological and cognitive correlates of ICDs in PD. Some of these findings may inform possible courses of action for care providers working with PD patients with ICDs. The literature on ICDs in non-PD populations may also be informative in this regard. The goals of the present article are to outline important clinical characteristics of ICDs in PD, briefly review relevant neurocognitive and neurobiological studies and discuss possible ways to prevent and manage ICDs in PD.
Dopaminergic medication-related Impulse Control Disorders (ICDs) such as pathological gambling and compulsive shopping have been reported in Parkinson disease (PD).
We hypothesized that dopamine agonists (DAs) would be associated with greater impulsive choice, or greater discounting of delayed rewards, in PD patients with ICDs (PDI).
Fourteen PDI patients, 14 PD controls without ICDs and 16 medication-free matched normal controls were tested on (i) the Experiential Discounting Task (EDT), a feedback-based intertemporal choice task, (ii) spatial working memory and (iii) attentional set shifting. The EDT was used to assess impulsivity choice (hyperbolic K-value), reaction time (RT) and decision conflict RT (the RT difference between high conflict and low conflict choices). PDI patients and PD controls were tested on and off DA.
On the EDT, there was a group by medication interaction effect [F(1,26)=5.62; p=0.03] with pairwise analyses demonstrating that DA status was associated with increased impulsive choice in PDI patients (p=0.02) but not in PD controls (p=0.37). PDI patients also had faster RT compared to PD controls F(1,26)=7.51 p=0.01]. DA status was associated with shorter RT [F(3,24)=8.39, p=0.001] and decision conflict RT [F(1,26)=6.16, p=0.02] in PDI patients but not in PD controls. There were no correlations between different measures of impulsivity. PDI patients on DA had greater spatial working memory impairments compared to PD controls on DA (t=2.13, df=26, p=0.04).
Greater impulsive choice, faster RT, faster decision conflict RT and executive dysfunction may contribute to ICDs in PD.
dopamine agonist; gambling; impulse control; Parkinson disease; delay discounting
Questions exist regarding the validity of patient-reporting of psychiatric symptoms in Parkinson’s disease (PD). We assessed observer variability and validity in reporting of impulse control disorder (ICD) symptoms in PD by using the Questionnaire for Impulsive-Compulsive Disorders in Parkinson’s Disease (QUIP). PD patients and their informants (71 pairs) completed the QUIP to assess four ICDs (compulsive gambling, buying, sexual behavior, and eating) in patients. Trained raters then administered a diagnostic interview. Sensitivity of the QUIP for a diagnosed ICD was 100% for both patient- and informant-completed instruments, and specificity was 75% for both raters. Approximately 40% of patients without an ICD diagnosis had a positive QUIP, suggesting that many PD patients experience subsyndromal ICD symptoms that require ongoing monitoring. Agreement between patient- and informant-reporting of any ICD behaviors on the QUIP was moderate (kappa = 0.408), and for individual ICDs was highest for gambling (kappa = 0.550). Overall, a negative QUIP from either the patient or informant rules out the possibility of an ICD, while a positive QUIP requires a follow-up diagnostic interview and ongoing monitoring to determine if symptoms currently are, or in the future become, clinically significant.
Impulse control disorders; Parkinson’s disease; QUIP
Impulse control disorders (ICDs) constitute a heterogeneous group of conditions linked diagnostically by difficulties in resisting “the impulse, drive, or temptation to perform an act that is harmful to the person or to others.” Specific ICDs share clinical, phenomenological and biological features with obsessive-compulsive disorder (OCD) that have suggested that these disorders might be categorized together. However, other data suggest significant differences between OCD and ICDs. In this article, clinical, phenomenological and biological features of the formal ICDs are reviewed and compared and contrasted with those of OCD. Available data indicate substantial differences between ICDs and OCD that suggest independent categorizations. Existing research gaps are identified and avenues for future research suggested.
obsessive compulsive disorder; impulse control disorders; addiction; nomenclature; impulsivity; compulsivity; aggression; gambling
In patients with Parkinson's disease, aberrant or excessive dopaminergic stimulation is commonly indicated as the trigger factor in unmasking impulse control disorders (ICDs) such as pathological gambling. We had the opportunity to follow a patient who experienced Parkinson's disease 7 years ago when he was using pramipexole and again, recently, when he was treated with levodopa (L-dopa) and low frequency stimulation of the nucleus of the pedunculopontine tegmentus (PPTg) but no dopamine agonists. The same patient had shown, when studied with fluorodeoxyglucose-positron emission tomography in the condition PPTg-ON, a peculiar increased activity in the left ventral striatum. This case report confirms that, in a predisposed personality, ICD may arise from the perturbation of endogenous pathways, which connect the brainstem to the basal ganglia.
To describe, in the context of DSM-V, how a focus on addiction and compulsion is emerging in the consideration of pathological gambling (PG).
A systematic literature review of evidence for the proposed re-classification of PG as an addiction.
Findings include: 1. Phenomenological models of addiction highlighting a motivational shift from impulsivity to compulsivity associated with a protracted withdrawal syndrome and blurring of the ego-syntonic/ego-dystonic dichotomy; 2. Common neurotransmitter (dopamine, serotonin) contributions to PG and substance use disorders (SUDs); 3. Neuroimaging support for shared neurocircuitries between “behavioral” and substance addictions and differences between obsessive-compulsive disorder (OCD), impulse control disorders (ICDs) and SUDs; 4. Genetic findings more closely related to endophenotypic constructs like compulsivity and impulsivity than to psychiatric disorders; 5. Psychological measures such as harm avoidance identifying a closer association between SUDs and PG than with OCD; 6. Community and pharmaco-therapeutic trials data supporting a closer association between SUDs and PG than with OCD. Adapted behavioral therapies, such as exposure therapy appear applicable to OCD, PG, or SUDs, suggesting some commonalities across disorders.
PG shares more similarities with SUDs than with OCD. Similar to the investigation of impulsivity, studies of compulsivity hold promising insights concerning the course, differential diagnosis and treatment of PG, SUDs, and OCD.
Compulsivity; Impulsivity; Addiction; Pathological Gambling; Endophenotypes
Impulse control disorders (ICDs) are potentially serious side effects of dopamine agonist therapy in Parkinson’s disease (PD), but prospective data are lacking about their incidence, time course, and risk factors. This work was a 4-year, prospective cohort study of outpatients with PD and no previous ICDs (N = 164). All subjects treated with a dopamine agonist during the study were followed longitudinally for new-onset ICDs. Baseline characteristics were compared in groups with (ICD+) and without (ICD−) subsequent ICDs. Forty-six subjects were treated with a dopamine agonist, including 25 who were newly treated and 21 who received ongoing dopamine agonist therapy. Of these 46 subjects, 18 (39.1%) developed new-onset ICDs. The timing of ICD onset varied from 3.0 to 114.0 months (median, 23.0) after initiation of dopamine agonist therapy. Baseline demographic characteristics were similar in ICD+ and ICD− groups. At baseline, ICD+ subjects had a greater prevalence of motor complications (61.1% versus 25.0%; P = 0.01) than ICD− subjects, despite comparable total dopaminergic medication usage in both groups (median, 150.0 versus 150.0 levodopa equivalents; P = 0.61). Compared with ICD− subjects, ICD+ subjects had a greater baseline prevalence of caffeine use (100% versus 66.7%; P = 0.007) and higher lifetime prevalence of cigarette smoking (44.4% versus 14.3%; P = 0.04). Peak dopamine agonist doses were higher in ICD+ than ICD− subjects (median 300.0 versus 165.0 L-dopa equivalents; P = 0.03), but cumulative dopamine agonist exposure was similar in both groups. In summary, the timing of new-onset ICDs in PD is highly variable. Risk factors include cigarette smoking, caffeine use, motor complications, and higher peak dopamine agonist dosage.
dopamine agonist; dopamine agonist withdrawal syndrome; impulse control disorder; prospective; Parkinson’s disease
Impulse control disorders (ICD) (most commonly pathologic gambling, hypersexuality, and uncontrollable spending) and compulsive behaviors can be triggered by dopaminergic therapies in Parkinson disease (PD). ICD are especially prevalent in patients receiving a dopamine agonist as part of their treatment regimen for PD, and have also been reported when dopamine agonists are used for other indications (e.g., restless legs syndrome). Although these iatrogenic disorders are common, affecting 1 in 7 patients with PD on dopamine agonists, they often elude detection by the treating physician. ICD lead to serious consequences, causing significant financial loss and psychosocial morbidity for many patients and families. ICD can appear at any time during treatment with dopamine agonists, sometimes within the first few months, but most often after years of treatment, particularly when patients receive dopamine agonists and levodopa together. In most cases ICD resolve if the dopamine agonist is withdrawn, and PD motor symptoms are managed with levodopa monotherapy. Familiarity with the clinical aspects, risk factors, pathophysiology, and management of ICD is essential for physicians using dopaminergic therapies to treat PD and other disorders.
There is an increasing awareness that impulse control disorders (ICDs), including compulsive gambling, buying, sexual behavior, and eating, can occur as a complication of Parkinson’s disease (PD). In addition, other impulsive or compulsive disorders have been reported to occur, including dopamine dysregulation syndrome (DDS) and punding. Case reporting and prospective studies have reported an association between ICDs and the use of dopamine agonists (DAs), particularly at greater dosages, whereas dopamine dysregulation syndrome has been associated with greater dosages of levodopa or short-acting DAs. Data suggest that risk factors for an ICD may include male sex, younger age or younger age at PD onset, a pre-PD history of ICD symptoms, personal or family history of substance abuse or bipolar disorder, and a personality style characterized by impulsiveness. Although psychiatric medications are used clinically in the treatment of ICDs, there is no empiric evidence supporting their use in PD. Therefore, management for clinically significant ICD symptoms should consist of modifications to dopamine replacement therapy, particularly DAs, and there is emerging evidence that such management is associated with an overall improvement in ICD symptomatology. It is important that PD patients be aware that DA use may lead to the development of an ICD, and that clinicians monitor patients as part of routine clinical care. As empirically validated treatments for ICDs are emerging, it will be important to examine their efficacy and tolerability in individuals with cooccurring PD and ICDs.
Impulsive–compulsive disorders such as pathological gambling, hypersexuality, compulsive eating, and shopping are side effects of the dopaminergic therapy for Parkinson’s disease. With a lower prevalence, these disorders also appear in the general population. Research in the last few years has discovered that these pathological behaviors share features similar to those of substance use disorders (SUD), which has led to the term “behavioral addictions”. As in SUDs, the behaviors are marked by a compulsive drive toward and impaired control over the behavior. Furthermore, animal and medication studies, research in the Parkinson’s disease population, and neuroimaging findings indicate a common neurobiology of addictive behaviors. Changes associated with addictions are mainly seen in the dopaminergic system of a mesocorticolimbic circuit, the so-called reward system. Here we outline neurobiological findings regarding behavioral addictions with a focus on dopaminergic systems, relate them to SUD theories, and try to build a tentative concept integrating genetics, neuroimaging, and behavioral results.
Behavioral addictions; Pathological gambling; Binge eating; Compulsive buying; Hypersexuality; Substance use disorders; Mesocorticolimbic circuit; Reward system; Dopamine; Parkinson; Parkinson’s disease; Neurobiology; Risk factors; Impulse control disorders; Functional anatomy
Risk-taking behavior is characterized by pursuit of reward in spite of potential negative consequences. Dopamine neurotransmission along the mesocorticolimbic pathway is a potential modulator of risk behavior. In patients with Parkinson's Disease (PD), impulse control disorder (ICD) can result from dopaminergic medication use, particularly Dopamine Agonists (DAA). Behaviors associated with ICD include hypersexuality as well as compulsive gambling, shopping, and eating, and are potentially linked to alterations to risk processing. Using the Balloon Analogue Risk task, we assessed the role of agonist therapy on risk-taking behavior in PD patients with (n=22) and without (n=19) active ICD symptoms. Patients performed the task both ‘on’ and ‘off’ DAA. DAA increased risk-taking in PD patients with active ICD symptoms, but did not affect risk behavior of PD controls. DAA dose was also important in explaining risk behavior. Both groups similarly reduced their risk-taking in high compared to low risk conditions and following the occurrence of a negative consequence, suggesting that ICD patients do not necessarily differ in their ability to process and adjust to some aspects of negative consequences. Our findings suggest dopaminergic augmentation of risk-taking behavior as a potential contributing mechanism for the emergence of ICD in PD patients.
Impulse Control Disorders; Dopamine Agonists; Parkinson Disease; Risk behavior
The presynaptic protein alpha-synuclein, associated with Parkinson's Disease (PD), plays a role in dopaminergic neurotransmission and is implicated in impulse control disorders (ICDs) such as drug addiction. In this study we investigated a potential causal relationship between alpha-synuclein and impulsivity, by evaluating differences in motor impulsivity in the 5-choice serial reaction time task (5-CSRTT) in strains of mice that differ in the expression of the alpha-synuclein gene. C57BL/6JOlaHsd mice differ from their C57BL/6J ancestors in possessing a chromosomal deletion resulting in the loss of two genes, snca, encoding alpha-synuclein, and mmrn1, encoding multimerin-1. C57BL/6J mice displayed higher impulsivity (more premature responding) than C57BL/6JOlaHsd mice when the pre-stimulus waiting interval was increased in the 5-CSRTT. In order to ensure that the reduced impulsivity was indeed related to snca, and not adjacent gene deletion, wild type (WT) and mice with targeted deletion of alpha-synuclein (KO) were tested in the 5-CSRTT. Similarly, WT mice were more impulsive than mice with targeted deletion of alpha-synuclein. Interrogation of our ongoing analysis of impulsivity in BXD recombinant inbred mouse lines revealed an association of impulsive responding with levels of alpha-synuclein expression in hippocampus. Expression of beta- and gamma-synuclein, members of the synuclein family that may substitute for alpha-synuclein following its deletion, revealed no differential compensations among the mouse strains. These findings suggest that alpha-synuclein may contribute to impulsivity and potentially, to ICDs which arise in some PD patients treated with dopaminergic medication.
Alpha-synuclein; impulse control disorders; impulsivity; Parkinson's disease