Abnormal arm swing movements in Parkinson's disease: onset, progression and response to L-Dopa

Abstract

Background: Reduced arm swing movements during gait are an early motor manifestation of Parkinson's disease (PD). The clinical evolution, response to L-Dopa and pathophysiological underpinning of abnormal arm swing movements in PD remain largely unclear. By using a network of wearable sensors, this study objectively assesses arm swing movements during gait in PD patients across different disease stages and therapeutic conditions.

Methods: Twenty healthy subjects (HS) and 40 PD patients, including 20 early-stage and 20 mid-advanced subjects, underwent a 6-m Timed Up and Go test while monitored through a network of wearable inertial sensors. Arm swing movements were objectively evaluated in both hemibodies and different upper limb joints (shoulder and elbow), using specific time-domain (range of motion and velocity) and frequency-domain measures (harmonics and total harmonic distortion). To assess the effects of L-Dopa, patients under chronic dopaminergic therapy were randomly examined when OFF and ON therapy. Finally, clinical-behavioral correlations were investigated, primarily focusing on the relationship between arm swing movements and cardinal L-Dopa-responsive motor signs, including bradykinesia and rigidity.

Results: Compared to HS, the whole group of PD patients showed reduced range of motion and velocity, alongside increased asymmetry of arm swing movements during gait. Additionally, a distinct increase in total harmonic distortion was found in patients. The kinematic changes were prominent in the early stage of the disease and progressively worsened owing to the involvement of the less affected hemibody. The time- and frequency-domain abnormalities were comparable in the two joints (i.e., shoulder and elbow). In the subgroup of patients under chronic dopaminergic treatment, L-Dopa restored patterns of arm swing movements. Finally, the kinematic alterations in arm swing movements during gait correlated with the clinical severity of bradykinesia and rigidity.

Conclusions: Arm swing movements during gait in PD are characterized by narrow, slow, and irregular patterns. As the disease progresses, arm swing movements deteriorate also in the less affected hemibody, without any joint specificity. The positive response to L-Dopa along with the significant correlation between kinematics and bradykinesia/rigidity scores points to the involvement of dopaminergic pathways in the pathophysiology of abnormal arm swing movements in PD.

Keywords: Arm swing; Bradykinesia; Parkinson’s disease; Rigidity; Wearable sensors.

Fig. 1

Wearable sensors placement. Arm swing movements were recorded using five sensors positioned on the forearms (S2, S5), upper arms (S3, S4), and trunk (S1)

Fig. 2

Time-domain analysis of arm swing movements. The figure depicts the spatiotemporal parameters of arm swing movements in healthy subjects (HS) and all patients with Parkinson’s disease (PD). (a) Shoulder range of motion (ROM) comparison; (b) Elbow ROM comparison; (c) Shoulder swing velocity comparison; (d) Elbow swing velocity comparison; (e) Shoulder asymmetry comparison; (f) Elbow asymmetry comparison. Error bars represent the standard deviation. *p < 0.05, **p < 0.01

Fig. 3

Subgroup time-domain analysis of arm swing movements. The figure depicts the spatiotemporal parameters of arm swing movements in healthy subjects (HS) and subgroups of patients with Parkinson’s disease, including drug naïve early-stage patients (PD_DN), mid-advanced PD patients under (PD_ON) and not under (PD_OFF) dopaminergic therapy. (a) Shoulder range of motion (ROM) subgroup comparison; (b) Elbow ROM subgroup comparison; (c) Shoulder swing velocity subgroup comparison; (d) Elbow swing velocity subgroup comparison; (e) Shoulder asymmetry subgroup comparison; (f) Elbow asymmetry subgroup comparison. Error bars represent the standard deviation. *p < 0.05, **p < 0.01

Fig. 4

Frequency-domain analysis of arm swing movements. The figure depicts the total harmonic distortion (THD) of arm swing movements in healthy subjects (HS), all patients with Parkinson’s disease (PD), drug-naïve early-stage individuals (PD_DN), mid-advanced PD patients under (PD_ON) and not under (PD_OFF) dopaminergic therapy. (a) Shoulder THD PD vs. HS comparison; (b) Elbow THD PD vs. HS comparison; (c) Shoulder THD subgroup comparison; (d) Elbow THD subgroup comparison; (e) Shoulder THD subgroup comparison; (f) Elbow THD subgroup comparison. Error bars represent the standard deviation. *p < 0.05, **p < 0.01

Fig. 5

Clinical-behavioral correlations. The scatterplot diagrams report clinical-behavioral correlation between kinematic parameters and upper limb motor impairment as reflected by MDS-UPRDS-III scores. (a) Shoulder range of motion (ROM) correlation; (b) Elbow range of motion (ROM) correlation; (c) Total harmonic distortion (THD) correlation; (d) Forearm total harmonic distortion (THD)