Impulse Control Disorders and Related Complications of Parkinson's Disease Therapy

Three paradoxes related to the mode of action of pramipexole: The path from D2/D3 dopamine receptor stimulation to modification of dopamine-modulated functions

Pramipexole, a D2/D3 dopamine receptor agonist, is used to treat the motor symptoms of Parkinson's disease, caused by degeneration of the dopaminergic nigrostriatal pathway. There are three paradoxes associated with its mode of action. Firstly, stimulation of D2/D3 receptors leads to neuronal inhibition, although pramipexole does not inhibit but promotes some dopamine-modulated functions, such as locomotion and reinforcement. Secondly, another dopamine-modulated function, arousal, is not promoted but inhibited by pramipexole, leading to sedation. Thirdly, pramipexole-evoked sedation is associated with an increase in pupil diameter, although sedation is expected to cause pupil constriction. To resolve these paradoxes, the path from stimulation of D2/D3 receptors to the modification of dopamine-modulated functions has been tracked. The functions considered are modulated by midbrain dopaminergic nuclei: locomotion - substantia nigra pars compacta (SNc), reinforcement/motivation - ventral tegmental area (VTA), sympathetic activity (as reflected in pupil function) - VTA; arousal - ventral periaqueductal grey (vPAG), with contributions from VTA and SNc. The application of genetics-based molecular techniques (optogenetics and chemogenetics) has enabled tracing the chains of neurones from the dopaminergic nuclei to their final targets executing the functions. The functional neuronal circuits linked to the D2/D3 receptors in the dorsal and ventral striata, stimulated by inputs from SNc and VTA, respectively, may explain how neuronal inhibition induced by pramipexole is translated into the promotion of locomotion, reinforcement/motivation and sympathetic activity. As the vPAG may increase arousal mainly by stimulating cortical D1 dopamine receptors, pramipexole would stimulate only presynaptic D2/D3 receptors on vPAG neurones, curtailing their activity and leading to sedation.

Sub-second Dopamine Signals during Risky Decision-Making in Patients with Impulse Control Disorder

Background

Impulse Control Disorder (ICD) in Parkinson's disease is a behavioral addiction arising secondary to dopaminergic therapies, most often dopamine receptor agonists. Prior research implicates changes in striatal function and heightened dopaminergic activity in the dorsal striatum of patients with ICD. However, this prior work does not possess the temporal resolution required to investigate dopaminergic signaling during real-time progression through various stages of decision-making involving anticipation and feedback.

Methods

We recorded high-frequency (10Hz) measurements of extracellular dopamine in the striatum of patients with (N=3) and without (N=3) a history of ICD secondary to dopamine receptor agonist therapy for Parkinson's disease symptoms. These measurements were made using carbon fiber microelectrodes during awake DBS neurosurgery and while participants performed a sequential decision-making task involving risky investment decisions and real monetary gains and losses. Per clinical standard-of-care, participants withheld all dopaminergic medications prior to the procedure.

Results

Patients with ICD invested significantly more money than patients without ICD. On each trial, patients with ICD made smaller adjustments to their investment levels compared to patients without ICD. In patients with ICD, dopamine levels rose or fell on sub-second timescales in anticipation of investment outcomes consistent with increased or decreased confidence in a positive outcome, respectively; dopamine levels in patients without ICD were significantly more stable during this phase. After outcome revelation, dopamine levels in patients with ICD rose significantly more than in inpatients without ICD for better-than-expected gains. For worse-than-expected losses, dopamine levels in patients with ICD remained level whereas dopamine levels in patients without ICD fell.

Conclusion

We report significantly increased risky behavior and exacerbated phasic dopamine signaling, on sub-second timescales, anticipating and following the revelation of the outcomes of risky decisions in patients with ICD. Notably, these results were obtained when patients who had demonstrated ICD in the past but were, at the time of surgery, in an off-medication state. Thus, it is unclear whether observed signals reflect an inherent predisposition for ICD that was revealed when dopamine receptor agonists were introduced or whether these observations were caused by the introduction of dopamine receptor agonists and the patients having experienced ICD symptoms in the past. Regardless, future work investigating dopamine's role in human cognition, behavior, and disease should consider the signals this system generates on sub-second timescales.

Risk of impulse control disorders in patients with Cushing's disease: do not blame cabergoline but do not give up caution

PURPOSE

To asses risk of new-onset impulse control disorders (ICDs) in patients with Cushing's disease (CD) who initiated cabergoline (CBG) and to determine frequency of ICDs in CBG-treated patients with CD.

METHODS

This naturalistic observational study had prospective and cross-sectional arms which included patients at five referral centers based in Istanbul. Patients who were scheduled for CBG were assigned to prospective arm. These patients underwent neuropsychological tests (Barratt Impulsiveness Scale, Minnesota Impulsive Disorders Interview, Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease-Rating Scale, Go/No-Go Task, Iowa Gambling Task, and Short Penn Continuous Performance Test) for assessment of impulsivity and psychiatric evaluations at baseline, 3, 6, and 12 months of CBG treatment. Impulsivity and new-onset ICDs were prospectively assessed. Patients with CD with current CBG treatment for ≥ 3 months and matched CBG-naïve patients with CD were included in cross-sectional arm. These patients underwent the same neuropsychological and psychiatric assessments. The impulsivity and frequency of ICDs were compared between CBG-treated and CBG-naïve patients with CD.

RESULTS

The follow-up duration of prospective cohort (n = 14) was 7.3 ± 2.3 months. One patient developed major depressive episode and another patient developed compulsive gambling after CBG. We observed no significant changes in impulsivity scores during follow-up. In cross-sectional arm, CBG-treated (n = 34) and CBG-naïve patients (n = 34) were similar in impulsivity scores and frequency of ICDs [3 patients (8.8%) vs. 2 patients (5.9%) respectively, p = 1.0].

CONCLUSION

CBG-treated patients with CD appeared to have a low risk of ICDs, suggesting that CBG still holds promise as a safe agent in CD.

Behavioral excess and disruptive conduct: A historical and taxonomic approach to the origin of the 'impulse control disorders' diagnostic construct

AIMS

Impulse control disorders (ICDs) are iatrogenic and idiopathic conditions with psychosocial and economic consequences for the affected individuals and their families (e.g. bankruptcy and divorce). However, the definition of ICDs has changed over time, and ICDs are not consistently included within existing taxonomies. We discuss the origins of the ICD diagnostic construct and its unsolved tensions.

METHODS

To contextualize the ICD diagnostic construct, we provided an overview of its origins in past centuries and followed its development across multiple editions of the Diagnostic and Statistical Manual and the International Classification of Diseases, as well as its definition within emerging ontologies.

RESULTS

Two independent roots of the ICD construct emerged: (a) the interest in behavioral excess as expressed in encyclopedic compilations (18th century) and (b) the juridical debate on disruptive conduct and responsibility (19th-20th centuries). These roots underlie the repeated taxonomic remodeling observed throughout the 20th and 21st centuries and three critical issues persisting in both clinical practice and research. First, the number of ICDs keeps increasing across the spectrum of human behaviors, disregarding common pathogenetic and phenomenological grounds. Secondly, ICDs substantially overlap with other mental conditions. Impulsivity is often neglected as a minor inconvenience or side effect when co-occurring with major diagnoses (e.g. depression) and therefore inadequately managed. Finally, ICDs' definitions display an unsolved tension between being conceived as hobby, moral fault or pathological drive, which may be responsible for stigma and delayed intervention.

CONCLUSION

The reasons that made impulse control disorders (ICDs) difficult to define from their first conceptualization are the same reasons that now complicate taxonomic efforts and diagnosis. Tracing back ICDs' roots and criticalities can help to define a common and less ambiguous theoretical framework, which may also result in the demise of the ICD construct and a move towards more clearly defined and more useful ontologies.

Exploring the underlying mechanisms of drug-induced impulse control disorders: a pharmacovigilance-pharmacodynamic study

INTRODUCTION

Impulse control disorders (e.g. pathological gambling, hypersexuality) may develop as adverse reactions to drugs. Pathogenetic hypotheses have mainly focused on D3-receptor agonism, and switching to alternatives with different pharmacologic mechanisms represents a common management strategy. Nonetheless, treatment failure is common and gaining pathophysiological insights is needed.

AIM

We aimed to identify targets potentially contributing to pathologic impulsivity.

METHOD

We performed a pharmacovigilance-pharmacodynamic study on dopamine agonists and antipsychotics using the Food and Drug Administration Adverse Event Reporting System (January 2004-December 2021). We estimated disproportionate reporting using the Bayesian information component. Using online public databases (IUPHAR, ChEMBL, PDSP, DrugBank), we calculated drug occupancies. To identify the targets potentially contributing to impulsivity, we fitted univariate regression models interpolating information components and occupancies within dopamine agonists and antipsychotics. Sensitivity analyses were performed to check for the robustness of the results.

RESULTS

Among 19 887 reports of impulsivity, 5898 recorded an antipsychotic, and 3100 a dopamine agonist. The more robust signals concerned aripiprazole (N = 3091; median information component [95% confidence interval] = 4.51[4.45-4.55]) and brexpiprazole (229; 4.00[3.78-4.16]) for antipsychotics, pergolide (105; 5.82[5.50-6.06]) and pramipexole (2009; 5.43[5.36-5.48]) for dopamine agonists. Robust, significant positive associations between drug occupancy and impulsivity reporting were found for D3 within dopamine agonists (beta = 1.52; P-value = 0.047) and 5-HT1a within antipsychotics (1.92, 0.029).

CONCLUSION

Our results supported the role of D3-receptor agonism in inducing impulsivity in dopamine receptor agonists and identified a potential role of 5-HT1a receptor agonism in antipsychotics. Investigating these receptors may drive towards a better management of drug-induced impulsivity.

Nutritional status and food consumption of patients with Parkinson disease

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease that affects food intake as the disease progresses. The assessment of nutritional status is essential to identify early nutritional deficits.

OBJECTIVE

To investigate the nutritional status and food intake of patients diagnosed with PD.

METHODS

This was a descriptive, cross-sectional, and quantitative study. A structured questionnaire with restricted questions was applied to identify the sociodemographic profile and anthropometric measurements were taken. To evaluate the disease stage, the modified Hoehn & Yahr scale was used. Food intake was evaluated using the Food Frequency Questionnaire (FFQ). The acquired information was organized in the Microsoft Office Excel 2010 program and statistical analysis was performed using the BioEstat 5.3 program.

RESULTS

The research was carried out with 40 patients; the majority was male (60%), over 60 years old (52.5%), single (55%), with a high school degree (42.5%), retirees (80%), and receiving one minimum salary (42.5%). Most were classified with eutrophic (42.5%) and overweight (42.5%). About food consumption, the most common foods were banana (60%), fish (52.5%), acerola (45%), and orange (32%). Among the high-risk foods, red meat (82.5%), fried foods (30%), heavy cream (25%), and filled sandwich cookies (25%) were the most common.

CONCLUSIONS

Most patients had a high consumption of red meat and processed foods, with relevant consumption of some fruits and low consumption of grains and oilseeds. The disease stage was not associated with nutritional status.

The Thermodynamic Consequences of Parkinson's Disease

Several lines of evidence point to a pervasive disturbance of energy balance in Parkinson's disease (PD). Weight loss, common and multifactorial, is the most observable sign of this. Bradykinesia may be best understood as an underinvestment of energy in voluntary movement. This accords with rodent experiments that emphasise the importance of dopamine in allocating motor energy expenditure. Oxygen consumption studies in PD suggest that, when activities are standardised for work performed, these inappropriate energy thrift settings are actually wasteful. That the dopaminergic deficit of PD creates a problem with energy efficiency highlights the role played by the basal ganglia, and by dopamine, in thermodynamic governance. This involves more than balancing energy, since living things maintain their internal order by controlling transformations of energy, resisting probabilistic trends to more random states. This review will also look at recent research in PD on the analysis of entropy-an information theory metric of predictability in a message-in recordings from the basal ganglia. Close relationships between energy and information converge around the concept of entropy. This is especially relevant to the motor system, which regulates energy exchange with the outside world through its flow of information. The malignant syndrome in PD, a counterpart of neuroleptic malignant syndrome, demonstrates how much thermodynamic disruption can result from breakdown of motor signalling in an extreme hypodopaminergic state. The macroenergetic disturbances of PD are consistent with a unifying hypothesis of dopamine's neurotransmitter actions-to adapt energy expenditure to prevailing economic circumstances.

Impulsive conditions in Parkinson's disease: A pharmacosurveillance-supported list

BACKGROUND

"Impulse Control Disorders" are behavioral conditions (e.g., gambling, hypersexuality), which are increasingly reported as reactions to dopamine agonists in Parkinson's disease. The Questionnaire for Impulsive-Compulsive Disorders in Parkinson's disease focuses only on 6 behaviors. Nonetheless, impulsivity could affect the entire range of human practices. Because of their heterogeneity and undefined boundaries, it is not clear what conditions should be considered as Impulse Control Disorders. This results in poorly standardized scientific literature and underdiagnosis.

OBJECTIVE

We aimed to create a comprehensive list of possible manifestations of drug-induced Impulse Control Disorders in Parkinson's disease and test it on pharmacosurveillance data.

METHODS

PubMed was used to identify reviews in English about Impulse Control Disorders in Parkinson's disease. Mentioned conditions were charted and translated to the lexicon of MedDRA, ICD-11, and DSM-5. The relevant MedDRA terms were used to test potential association with dopamine agonists on the FDA Adverse Event Reporting System.

RESULTS

50 reviews published between 2001 and 2020 were identified. 66 conditions were collected as possible Impulse Control Disorders. Pathological gambling, shopping, eating and sexuality, dopamine dysregulation syndrome, hobbyism and punding were the most frequently mentioned, together with leisure activities, body-focused compulsivity, disruptive, impulse control and conduct disorders, and substance abuse. All these conditions were disproportionately reported with dopamine agonists, except for substance abuse.

CONCLUSIONS

We defined a potential extended list of ICDs, which, along with its conversion to international taxonomies, can support the identification of drug-induced conditions in pharmacovigilance archives, as well as monitoring processes in clinical practice.

Dopamine Receptors in Parkinson's Disease: A Meta-Analysis of Imaging Studies

Dopamine receptors are abundant along the central nigrostriatal tract and are expressed as 5 subtypes in two receptor families. In PD, compensatory changes in dopamine receptors emerge as a consequence of the loss of dopamine nerve terminals or dopaminergic pharmacotherapy. We performed a systematic review and meta-analysis of the available PET and single-photon emission computed tomography studies that have investigated dopamine receptors in PD, PSP and MSA. The inclusion criteria were studies including human PET or single-photon emission computed tomography imaging; dopamine receptor tracers (D1-like or D2-like) and idiopathic PD, PSP, or MSA patients compared with healthy controls. The 67 included D2-like studies had 1925 patients. Data were insufficient for an analysis of D1-like studies. PD patients had higher striatal binding early in the disease, but after a disease duration of 4.36 years, PD patients had lower binding values than healthy controls. Striatal D2R binding was highest in unmedicated early PD patients and in the striatum contralateral to the predominant motor symptoms. PSP and MSA-P patients had lower striatal D2R binding than PD patients (14.2% and 21.8%, respectively). There is initial upregulation of striatal D2Rs in PD, which downregulate on average 4 years after motor symptom onset, possibly because of agonist-induced effects. The consistent upregulation of D2Rs in the PD striatum contralateral to the predominant motor symptoms indicates that receptor changes are driven by neurodegeneration and loss of striatal neuropil. Both PSP and MSA patients have clearly lower striatal D2R binding values than PD patients, which offers an opportunity for differential diagnostics. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Pathological gambling in a patient on piribedil: A case report

RATIONALE

Piribedil is an orally active dopamine agonist that has been widely used for Parkinson disease (PD), with its partial D2/D3 agonistic functions and alpha2-adrenoreceptor antagonistic effects, piribedil has been proved to be efficacious in the relief of motor symptoms in PD, while it can also lead to impulse control disorders such as pathological gambling due to its dopamine agonistic effects.

PATIENT CONCERNS

A 28-year-old Chinese female patient with Parkinson disease and a history of taking piribedil finally developed pathological gambling and depressive episode.

DIAGNOSES

After a careful clinical observation and evaluation, the patient met the criteria of severe depressive episode and pathological gambling due to antiparkinson therapy.

INTERVENTIONS

We discontinued piribedil and picked bupropion, a dopamine reuptake inhibitor, to alleviate the depressive symptom. Benzhexol and selegiline were also added for the control of motor fluctuations.

OUTCOMES

After 3 weeks' treatment, the patient's depressive mood was significantly alleviated and her recurring PD symptoms were also relieved. She was no more addicted to network gambling, and there was no recurrence during the 1-year follow-up.

LESSONS

Piribedil-induced problem gambling and impulse control disorders are side effects needed to be evaluated when commencing a patient on piribedil. This case further emphasizes the importance of monitoring and controlling Parkinson symptoms after drug reduction or withdrawal. Anticipation of this risk strengthens the significance of detailed medical history-taking and targeted clinical management.

Neuropsychiatric aspects of Parkinson disease psychopharmacology: Insights from circuit dynamics

Parkinson disease (PD) is a neurodegenerative disorder with a complex pathophysiology characterized by the progressive loss of dopaminergic neurons within the substantia nigra. Persons with PD experience several motoric and neuropsychiatric symptoms. Neuropsychiatric features of PD include depression, anxiety, psychosis, impulse control disorders, and apathy. In this chapter, we will utilize the National Institutes of Mental Health Research Domain Criteria (RDoC) to frame and integrate observations from two prevailing disease constructions: neurotransmitter anomalies and circuit physiology. When there is available evidence, we posit how unified translational observations may have clinical relevance and postulate importance outside of PD. Finally, we review the limited evidence available for pharmacologic management of these symptoms.

Non-toxic HSC Transplantation-Based Macrophage/Microglia-Mediated GDNF Delivery for Parkinson's Disease

Glial cell-line-derived neurotrophic factor (GDNF) is a potent neuroprotective agent in cellular and animal models of Parkinson’s disease (PD). However, CNS delivery of GDNF in clinical trials has proven challenging due to blood-brain barrier (BBB) impermeability, poor diffusion within brain tissue, and large brain size. We report that using non-toxic mobilization-enabled preconditioning, hematopoietic stem cell (HSC) transplantation-based macrophage-mediated gene delivery may provide a solution to overcome these obstacles. Syngeneic bone marrow HSCs were transduced ex vivo with a lentiviral vector expressing macrophage promoter-driven GDNF and transplanted into 14-week-old MitoPark mice exhibiting PD-like impairments. Transplant preconditioning with granulocyte colony-stimulating factor (G-CSF) and AMD3100 was used to vacate bone marrow stem cell niches. Chimerism reached ∼80% after seven transplantation cycles. Transgene-expressing macrophages infiltrated degenerating CNS regions of MitoPark mice (not wild-type littermate controls), resulting in increased GDNF levels in the midbrain. Macrophage GDNF delivery not only markedly improved motor and non-motor dysfunction, but also dramatically mitigated the loss of dopaminergic neurons in both substantia nigra and the ventral tegmental area and preserved axonal terminals in the striatum. Striatal dopamine levels were almost completely restored. Our data support further development of mobilization-enabled HSC transplantation (HSCT)-based macrophage-mediated GDNF gene delivery as a disease-modifying therapy for PD.

Resting state oscillations suggest a motor component of Parkinson's Impulse Control Disorders

OBJECTIVES

Impulse control disorders (ICDs) in Parkinson's disease (PD) have been associated with cognitive impulsivity and dopaminergic dysfunction and treatment. The present study tests the neglected hypothesis that the neurofunctional networks involved in motor impulsivity might also be dysfunctional in PD-ICDs.

METHODS

We performed blind spectral analyses of resting state electroencephalographic (EEG) data in PD patients with and without ICDs to probe the functional integrity of all cortical networks. Analyses were performed directly at the source level after blind source separation. Discrete differences between groups were tested by comparing patients with and without ICDs. Gradual dysfunctions were assessed by means of correlations between power changes and clinical scores reflecting ICD severity (QUIP score).

RESULTS

Spectral signatures of ICDs were found in the medial prefrontal cortex, the dorsal anterior cingulate and the supplementary motor area, in the beta and gamma bands. Beta power changes in the supplementary motor area were found to predict ICDs severity.

CONCLUSION

ICDs are associated with abnormal activity within frequency bands and cortical circuits supporting the control of motor response inhibition.

SIGNIFICANCE

These results bring to the forefront the need to consider, in addition to the classical interpretation based on aberrant mesocorticolimbic reward processing, the issue of motor impulsivity in PD-ICDs and its potential implications for PD therapy.

Compulsive eating behaviors in Parkinson's disease

PURPOSE

Eating disorders are common in Parkinson's disease (PD) patients and often class in Impulse control disorders, however, little is known about their phenomenology. Specific symptoms and comorbidities were described in a group of PD patients in this preliminary study.

METHODS

Over a period of 6 months, 51 PD patients who experienced significant changes in eating habits following diagnosis of PD and were interviewed during regularly scheduled follow-up visits. We assessed each patient's height and weight, impulsivity, psychological distress, current eating disorder symptoms, food addiction, food habits and craving.

RESULTS

Among the PD patients who experienced modified dietary habits following diagnosis, few exhibited binge eating disorders (BED) full criteria (3.9%). However, 21.6% of patients experienced episodes of out-of-control eating with a large quantity of food in short time and 39.2% satisfied food addiction (FA) criteria without binge eating disorder. Food cravings more than once a week were experienced in approximately half of the population including all FA patients. Regarding comorbidities, FA PD patients present impulsive features and anxiety.

CONCLUSIONS

This study confirms the existence of FA profile in PD patients. Eating disorders even in PD are complex and have a cross-cutting criteria related to out-of-control eating, FA, and BED. The association of anxiety with PD-related food addiction, contrary to L-dopa equivalent daily dose mean score or the presence of dopamine agonists, underline the complex sustainability of the dopaminergic brainstem support. A study on their detailed prevalence in this population could be helpful to better understand unspecified feeding or eating disorder.

CLINICAL TRIAL NUMBER

DR-2012-007.

NAME OF THE REGISTRY

French Committee for the Protection of Persons (CPP) & French National Commission on Computing and Liberty (CNIL).

LEVEL OF EVIDENCE

Level V, descriptive study.

Impulse Control Disorders in Parkinson's Disease. A Brief and Comprehensive Review

Impulse control and related disorders (ICDs-RD) encompasses a heterogeneous group of disorders that involve pleasurable behaviors performed repetitively, excessively, and compulsively. The key common symptom in all these disorders is the failure to resist an impulse or temptation to control an act or specific behavior, which is ultimately harmful to oneself or others and interferes in major areas of life. The major symptoms of ICDs include pathological gambling (PG), hypersexualtiy (HS), compulsive buying/shopping (CB) and binge eating (BE) functioning. ICDs and ICDs-RD have been included in the behavioral spectrum of non-motor symptoms in Parkinson's disease (PD) leading, in some cases, to serious financial, legal and psychosocial devastating consequences. Herein we present the prevalence of ICDs, the risk factors, its pathophysiological mechanisms, the link with agonist dopaminergic therapies and therapeutic managements.

Medications, Deep Brain Stimulation, and Other Factors Influencing Impulse Control Disorders in Parkinson's Disease

Impulse control disorders (ICDs) in Parkinson's disease (PD) have a high cumulative incidence and negatively impact quality of life. ICDs are influenced by a complex interaction of multiple factors. Although it is now well-recognized that dopaminergic treatments and especially dopamine agonists underpin many ICDs, medications alone are not the sole cause. Susceptibility to ICD is increased in the setting of PD. While causality can be challenging to ascertain, a wide range of modifiable and non-modifiable risk factors have been linked to ICDs. Common characteristics of PD patients with ICDs have been consistently identified across many studies; for example, males with an early age of PD onset and dopamine agonist use have a higher risk of ICD. However, not all cases of ICDs in PD can be directly attributable to dopamine, and studies have concluded that additional factors such as genetics, smoking, and/or depression may be more predictive. Beyond dopamine, other ICD associations have been described but remain difficult to explain, including deep brain stimulation surgery, especially in the setting of a reduction in dopaminergic medication use. In this review, we will summarize the demographic, genetic, behavioral, and clinical contributions potentially influencing ICD onset in PD. These associations may inspire future preventative or therapeutic strategies.

Impulse Control Disorders and Dopamine-Related Creativity: Pathogenesis and Mechanism, Short Review, and Hypothesis

Impulse control disorder (ICD), including pathological gambling, hypersexuality, and compulsive shopping has been linked to antiparkinsonian medication, especially dopamine agonists. The mechanism of ICD is not completely clear, but it seems that ICD is the result of an activation of dopamine receptors, mostly D3 in the ventral striatum. Patients treated with dopamine agonists that have preferential affinity for D3 (including ropinirole and pramipexole) are much more prone to develop ICD. In addition, a genetic component is probably present, especially in young patients. Finally, environment and lifestyle may also play a role: those patients engaged in physical, social, and artistic activities are probably less likely to develop ICD compared to those patients with poor physical activity living in isolated environments.

Disruption of Inferior Longitudinal Fasciculus Microstructure in Parkinson's Disease: A Systematic Review of Diffusion Tensor Imaging Studies

Parkinson's disease (PD) is a neurodegenerative disorder accompanied by a series of pathological mechanisms which contribute to a variety of motor and non-motor symptoms. Recently, there has been an increasing interest in structural diffusion tensor imaging (DTI) in PD which has shed light on our understanding of structural abnormalities underlying PD symptoms or its associations with pathological mechanisms. One of the white matter tracts shown to be disrupted in PD with a possible contribution to some PD symptoms is the inferior longitudinal fasciculus (ILF). On the whole, lower ILF integrity contributes to thought disorders, impaired visual emotions, cognitive impairments such as semantic fluency deficits, and mood disorders. This review outlines the microstructural changes in ILF associated with systemic inflammation and various PD symptoms like cognitive decline, facial emotion recognition deficit, depression, color discrimination deficit, olfactory dysfunction, and tremor genesis. However, few studies have investigated DTI correlates of each symptom and larger studies with standardized imaging protocols are required to extend these preliminary findings and lead to more promising results.

White Matter Tract Alterations in Drug-Naïve Parkinson's Disease Patients With Impulse Control Disorders

Impulse control disorders (ICDs) are relatively frequent in patients with Parkinson’s disease (PD), although it is still unclear whether an underlying pathological process plays a significant role in the development of ICD in PD apart from dopaminergic replacement therapy. In this study, we have investigated alterations of white matter tract in drug-naïve PD patients with ICDs via diffusion MRI connectometry. Our results showed that disrupted connectivity in the complex network of dynamic connections between cerebellum, basal ganglia, cortex, and its spinal projections serves as the underlying neuropathology of ICD in PD not interfered with the contribution of dopaminergic replacement therapy. These findings provide the first evidence on involved white matter tracts in the neuropathogenesis of ICD in drug-naïve PD population, supporting the hypothesis that neural disturbances intrinsic to PD may confer an increased risk for ICDs. Future studies are needed to validate the attribution of the impaired corticocerebellar network to impulsivity in PD.