Marcelo Merello

Background: Parkinson's disease (PD) bradykinesia is a complex of motor abnormalities. Subthalamic Nucleus Deep Brain Stimulation (STN‐DBS) and L‐dopa both improve bradykinesia, but their differential effects on each component remain unknown. Objective: To quantify and compare the differential effects of STN‐DBS and L‐dopa on the individual kinematic components of bradykinesia. Methods: PD patients with bilateral STN‐DBS were prospectively evaluated at least 3 months after surgery. Clinical and kinematic analyses of finger tapping were performed under three conditions: OFF, ON‐DBS (clinically optimized stimulation), and ON‐medication. Bradykinesia was decomposed into amplitude, velocity, dysrhythmia, sequence effect, hesitations, and interruptions. Data were analyzed using repeated‐measures ANOVA or Friedman tests, with adjusted post‐hoc comparisons. Results: Twenty patients with PD were evaluated: median follow‐up after surgery of 9.5 [3.75–11.5] months. Both L‐dopa and STN‐DBS significantly improved clinical MDS‐UPDRS finger‐tapping scores compared to baseline ( P < 0.001). STN‐DBS showed a significantly greater effect on interruptions ( P = 0.03), while L‐dopa only showed a greater effect on hesitations ( P = 0.03), compared with the OFF baseline. Dysrhythmia and sequence effect were unaffected by either therapy. When several features of bradykinesia were combined in a composite kinematic score, both therapies showed a significant difference compared with the OFF baseline ( P < 0.01). Conclusions: Despite comparable clinical efficacy, L‐dopa and STN‐DBS have different profiles of kinematic effects on the components of bradykinesia implicated in motor blocks. Understanding these distinctions is essential for refining motor assessments and developing therapies targeting specific pathophysiological mechanisms.

The definition of bruxism has evolved over the past few years. Currently, two clinical presentations are recognized: Sleep Bruxism (SB) and Awake Bruxism (AB). Although various bruxism assessment strategies have been developed to guide clinical practice, no specific, valid, reliable tool has been designed specifically for patients with AB. Aim: To design and validate a questionnaire to assess the presence, severity and symptomatology of AB. Secondary objectives included exploring the clinical and psychiatric manifestations of AB. Materials and Method: A prospective case-control study was conducted on 14 AB cases and 20 healthy controls. The presence or absence of the condition was confirmed by electromyographic study. A specific questionnaire for AB (AB-Q) was developed, and AB psychometric properties were evaluated. The AB-Q consists of 24 items grouped into four domains. The reliability, sensitivity and specificity of the AB-Q were assessed. Results: Significant differences were observed between groups: EMG-confirmed bruxism episodes were recorded in all 14 AB patients and none of the controls. The AB-Q showed high internal consistency (Cronbach’s alpha: 0.924) and strong discriminative capacity, with a sensitivity of 100% and a specificity of 90%. A significant association was found between bruxism and the presence of anxiety and depressive disorders, as well as obsessive-compulsive traits. Conclusion: The AB-Q questionnaire proved to be a useful tool with acceptable clinimetric properties for assessing the presence and severity of bruxism.

Background: Evidence on environmental determinants of Parkinson’s disease (PD) in Latin America is limited and their attributable burden remains poorly defined in the region. We examined associations between environmental exposures and PD and quantified their contribution to disease burden.Methods: We analyzed 9887 participants from nine Latin American countries in a case control study. Associations between environmental exposures and PD were estimated using logistic regression adjusted for age, sex, and country. Population attributable fractions (PAFs) were calculated for positively associated exposures, defined as severe head trauma or at least 5 years of exposure for other risk factors.Findings: Weekly caffeine consumption and tobacco use for at least 5 years were inversely associated with PD (adjusted OR [aOR] 0·77, p < 0·0001; aOR 0·83, p = 0·0009). Severe head trauma (aOR 1·35, p < 0·0001), occupational pesticide exposure (aOR 1·42, p = 0·0003), occupational metal exposure (aOR 1·29, p = 0·0299), rural living (aOR 1·60, p < 0·0001), and well water consumption (aOR 1·22, p = 0·0014) were positively associated with PD. Dose related associations were observed for caffeine, tobacco, occupational pesticides and metals, rural living, and well water consumption. The joint PAF across five risk exposures was 13·7% (95% CI 9·8 to 17·3), with higher estimates in El Salvador, Brazil, Colombia, males, and participants younger than 60 years. Sensitivity and lag analyses were directionally consistent.Interpretation: Selected environmental exposures may account for a meaningful proportion of PD burden in Latin America, supporting further research and public health attention to environmental determinants in the region.

Background: Although levodopa is the gold standard treatment for Parkinson's disease (PD), its chronic use is associated with levodopa-induced dyskinesia (LID), a motor complication that impacts prognosis, quality of life, and treatment costs. Most known LID-associated factors have been identified in European-descendant populations. Objectives: To describe the epidemiology of LID in Latin American and Caribbean (LATAM) countries and assess the relevance of known and novel LID-associated factors in this population. Methods: We conducted a cross-sectional study using data from the Latin American Research consortium on the Genetics of Parkinson's Disease (LARGE-PD). We included PD patients with information on LID status and levodopa use from eight LATAM countries. LID prevalence was calculated overall and by country. Countries were compared on demographic and clinical variables. Logistic regression was used to identify associations with LID. Results: A total of 3695 PD patients (58.8% male) were included. Overall LID prevalence was 25.4% [95% CI: 24.06–26.87], ranging from 9.3% in Colombia to 45.1% in Puerto Rico. Prevalence increased progressively with longer disease duration. Country comparisons showed that not all known LID-associated factors explained prevalence differences. In logistic regression, fast disease progression was significantly associated with LID (OR: 1.55, 95%CI: 1.16–2.07), while sex was not (OR: 1.02, 95%CI: 0.87–1.18). Conclusions: This is the largest study on LID epidemiology in LATAM. While some known risk factors remain relevant, others, like sex, do not, underscoring the need for population-specific studies. Future work should integrate environmental, clinical, and genetic data to better understand LID mechanisms.

Background Misdiagnosis of functional movement disorders (FMD) remains a concern for clinicians. We sought to review the phenomenology and clinical features associated with FMD misdiagnosis. Methods We conducted a systematic review of case reports, case series, and observational studies of adults diagnosed with FMD and subsequently reclassified as having another neurological or medical condition. PubMed was searched from inception to September 13, 2025, focusing on reported features of inconsistency, incongruence with known diseases, and low-validity features. Isolated (iMD) and mixed (mMD) movement disorders were analyzed separately. Results Forty-two included studies comprised 150 patients, of which 73 cases underwent detailed analysis. Gait disturbance (35%) and dystonia (27.5%) were the most common iMD phenomenologies (n = 40), while jerks and rigidity (24%) were the most common mMD phenomenology (n = 33). Incongruence with known diseases (50.7%), psychological factors (34.2%), and symptom variability (31.5%) were the main factors associated with misdiagnosis. Application of incongruence alone was associated with the highest rate of FMD misdiagnosis, similar to that of applying neither incongruence nor inconsistency (49% in both cases). Conversely, reliance on inconsistency alone was least associated with an FMD misdiagnosis (13.7%). Misdiagnoses of iMD were more likely in the absence of documented inconsistency (OR 3.94, 95% CI 1.32—12.82). Conclusions FMD misdiagnoses, particularly of gait disorders and dystonia, were most commonly associated with the application of incongruence as diagnostic criterion. The lowest rate of FMD misdiagnosis was associated with ascertaining at least two positive neurological signs of inconsistency.

Background: Levodopa‐induced dyskinesias (LIDs) are an important burden for patients with Parkinson's disease (PD), yet their mechanisms remain incompletely understood. Objective: The objective of this study was to investigate the temporal and spatial relationship between local field potential (LFP) changes and dyskinesia development in PD. Methods: We recorded bilateral subthalamic LFPs, electromyography, and accelerometry in patients with PD with peak‐dose LIDs undergoing deep brain stimulation (DBS) surgery. Apomorphine was administered to induce dyskinesias, and recordings continued for 200 seconds postonset. Spectral power changes were analyzed over time and mapped to the DBS “sweet spot.” A machine‐learning algorithm detected dyskinetic movements. Results: In 9 of 36 patients, dyskinesias were preceded by a bilateral beta power decrease ( P < 0.001) and contralateral theta increase ( P = 0.02), followed by gamma elevation ( P = 0.03). These changes peaked in the DBS sweet spot. Conclusions: Our results provide insights into the sequential nature of beta, theta, and gamma oscillatory changes. Theta activity may serve as a key biomarker for adaptive DBS. © 2025 International Parkinson and Movement Disorder Society.

Background: Awareness and major external events can contribute to the number of FMD cases. Objective: To analyze trends in new Functional Movement Disorders (FMD) consultations and the impact of the COVID‐19 pandemic. Methods: Retrospective analysis of FMD new consultations (2014–2024) at a tertiary movement disorders clinic. Trends and the COVID‐19 impact were analyzed with linear and segmented regression. Patient characteristics in the pre‐ and post‐pandemic periods were compared. Results: Among 14,587 new consultations, 162 were FMD (79% female, mean age at onset 44.7 ± 18.3 years). FMD consultations increased slowly over time, with a marked surge after 2021. The significant rise was observed during the three years post‐pandemic, followed by a return to the pre‐pandemic slope. Pre and post‐pandemic groups’ characteristics were almost similar. Conclusions: FMD consultations increased over time and significantly after the COVID‐19 pandemic. This underscores the influence of increased awareness and external factors.

Background: Although levodopa remains the gold standard treatment for Parkinson’s disease (PD), its chronic use is associated with levodopa-induced dyskinesia (LID), a motor complication that impacts prognosis, quality of life, and treatment costs. Most known LID-associated factors have been identified in European-descendant populations. Objectives: To describe the epidemiology of LID in Latin American and Caribbean (LATAM) countries and assess the relevance of known and novel LID-associated factors in this population. Methods: We conducted a cross-sectional study using data from the Latin American Research consortium on the Genetics of Parkinson’s Disease (LARGE-PD). We included PD patients with information on LID status and levodopa use from eight LATAM countries. LID prevalence was calculated overall and by country. Countries were compared on demographic and clinical variables. Logistic regression was used to identify associations with LID. Results: A total of 3,695 PD patients (58.8% male) were included. Overall LID prevalence was 25.4% [95% CI: 24.06–26.87], ranging from 9.3% in Colombia to 45.1% in Puerto Rico. Prevalence increased progressively with longer disease duration. Country comparisons showed that not all known LID-associated factors explained prevalence differences. In logistic regression, fast disease progression was significantly associated with LID (OR: 1.55, 95%CI: 1.16–2.07), while sex was not (OR: 1.02, 95%CI: 0.87–1.18). Conclusions: This is the largest study on LID epidemiology in LATAM. While some known risk factors remain relevant, others, like sex, do not, underscoring the need for population-specific studies. Future work should integrate environmental, clinical, and genetic data to better understand LID mechanisms.