Objective: The aim of this study is to objectively characterize and compare the temporal patterns of finger-tapping amplitude decrement in patients with Parkinson’s disease (PD) and healthy controls (HC).

Background: Bradykinesia, as a complex of motor abnormalities, represents the hallmark motor symptom of PD and is assessed using repetitive finger tapping (FT) tasks. Kinematic analysis shows that movement amplitude decrement (sequence effect) is a key, though variable, component of bradykinesia [1-3]. To date, the temporal pattern (“shape”) of amplitude decrement has not been characterized.

Method: We enrolled 109 patients with PD (mean age 66.6 ± 8.9) and 84 HC (mean age 66.9 ± 9.9). Participants performed three consecutive 15-second FT trials (dominant hand in HC; most affected side in PD OFF medication). Movements were recorded using an optoelectronic motion capture system with infrared cameras and reflective markers placed on predefined hand landmarks. Amplitude decrement (sequence effect) was analyzed across three temporal segments (0–5 sec, 5–10 sec, 10–15 sec).  Slopes were calculated for each segment and averaged across trials. Segments with slopes higher than -0.05 were classified as decremental. Based on the “shape” of the sequence effect, participants were categorized into six patterns: very early, early, stable, late, very late decrement, or no decrement. Group differences were assessed using chi-squared tests.

Results: The pattern distribution of sequence-effect “shapes” differed significantly between PD and HC (χ² = 19.7, p = 0.001). Patients more frequently exhibited a stable decrement pattern (χ² = 8.264, p = 0.004), whereas HC typically displayed no-decrement (χ² = 14.1, p = 0.0002). Beyond these patterns, patients showed earlier amplitude reduction compared to HC.

Conclusion: The sequence effect in PD shows a variable temporal pattern. Further studies and analyses should investigate whether these distinct profiles are related to specific clinical features, potentially informing better patient stratification and more targeted interventions.

References: [1] Bologna M, Espay AJ, Fasano A, Paparella G, Hallett M, Berardelli A. Redefining Bradykinesia. Mov Disord. 2023 Apr;38(4):551-557. doi: 10.1002/mds.29362.
[2] Paparella G, Cannavacciuolo A, Angelini L, Costa D, Birreci D, Alunni Fegatelli D, Guerra A, Berardelli A, Bologna M. May Bradykinesia Features Aid in Distinguishing Parkinson’s Disease, Essential Tremor, And Healthy Elderly Individuals? J Parkinsons Dis. 2023;13(6):1047-1060. doi: 10.3233/JPD-230119. PMID: 37522221; PMCID: PMC10578222.
[3] Panyakaew P, Duangjino K, Kerddonfag A, Ploensin T, Piromsopa K, Kongkamol C, Bhidayasiri R. Exploring the Complex Phenotypes of Impaired Finger Dexterity in Mild-to-moderate Stage Parkinson’s Disease: A Time-Series Analysis. J Parkinsons Dis. 2023;13(6):975-988. doi: 10.3233/JPD-230029. PMID: 37574743; PMCID: PMC10578277.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-shape-of-sequence-effect-in-parkinsons-disease/