Objective:

The purpose of this study was to compare the level and bilateral expression of upper arm rigidity between people with early stage Parkinson’s disease (PD) with and without abnormal elevation of rapid eye movement (REM) sleep without atonia (RSWA).

Background: People with PD and REM sleep behavior disorder (characterized by increased RSWA) typically present with an akinetic-rigid subtype of disease, are less responsive to medications, and may have faster disease progression (Postuma et al. 2008). This study tested the hypothesis that earlier and more extensive degeneration in nigrostriatal and brainstem systems may be expressed by worsening and increased asymmetry of rigidity. 

Methods: Clinical (MDS-UPDRS) and quantitative assessments of rigidity were obtained in 15 individuals with PD with either abnormally increased (RSWA+) or normative (RSWA-) muscle tone during REM sleep (based on polysomnogram). Quantitative measures of forearm rigidity were obtained using a robotic manipulandum that passively moved the forearm through a 80 deg. sinusoidal trajectory about the pronation-supination axis.  Two movement frequencies (1.0 and 1.5 Hz) and resistance conditions (passive and active facilitation during contralateral forearm tapping) were tested.  Two-way repeated measures ANOVAs were performed to test differences between groups and sides (more vs. less-affected) in both resistance conditions and movement frequencies.

Results: There were significant (p < 0.05) main effects of group and side x group interaction effects.  Post hoc analysis showed that rigidity was significantly increased in the RSWA+ vs. RSWA- groups.  Interactions effects showed that rigidity was reduced on the less-affected compared with the more-affected side in the RSWA- group (consistent with asymmetric presentation of disease), but the rigidity in the RSWA+ group was similar across both sides.

Conclusions: These findings suggest that not only is rigidity increased in people with early stage PD and abnormal RSWA, but abnormal tone is present more symmetrically.  The bilateral disruption of muscle tone regulation in both REM sleep and normal waking suggests brainstem involvement in both symptoms.

References: Postuma RB, Gagnon JF, Vendette M, Charland K, Montplaisir J. REM sleep behaviour disorder in Parkinson’s disease is associated with specific motor features. Journal of neurology, neurosurgery, and psychiatry 2008;79:1117-1121.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/increased-and-symmetric-expression-of-rigidity-in-early-parkinsons-disease-with-abnormal-rem-sleep-without-atonia/