Muscle ultrasound in idiopathic Parkinson's disease with deep brain stimulation: Rigidity can be quantified by shear wave elastography.

Question Rigidity is a cardinal symptom of Parkinson's disease (PD) and is evaluated subjectively by clinicians. By default, the Unified Parkinson’s Disease Rating Scale (UPDRS) is used, which varies even among experienced examiners. Remedy could be shear wave elastography (SWE): Here, tissue elasticity (simply speaking, stiffness) can be estimated non-invasively using an ultrasound device. Since rigidity is basically an increased stiffness of the muscles, it seems reasonable to investigate whether the increased muscle rigidity in PD can be objectified using SWE of the muscles.

Method Consequently, we performed a proof-of-principle study in 10 PD patients and 10 healthy controls; half of PD patients were treated invasively with deep brain stimulation (DBS) and the other half conservatively with levodopa. Patients were seated comfortably in a chair and shear wave velocity (SWV) was measured bilaterally at the biceps brachii muscle and flexor digitorum profundus muscle in rest and passive stretch in 5-minute-intervals longitudinally over a total period of 80 minutes. During this 80-minutes (i.e., 15 measurement time points), also UPDRS-III was evaluated, and rigidity was in- or decreased by turning the DBS on and off as well as administrating levodopa.

Results At group level, the overall SWE of the four examined muscles correlated only poorly with the UPDRS-III (r=0.1, p<0,001), but a specific analysis of individual muscles (e.g. right biceps brachii in passive stretch) showed a significant correlation (r=0.65, p<0.001), that the more pronounced the rigidity, the higher the SWE. On the individual level (i.e., single patient) occasionally, this correlation could rise up to r=0.81 (p<0.001) in left biceps brachii during passive stretch.

Conclustion We demonstrate that muscle ultrasound SWE – as a proof-of-principle – might be potentially a promising, non-invasive tool for the quantitative assessment of rigidity in PD (with and without DBS). Further studies with a standardized measurement setup including additional modalities (e.g., accelerometer, surface EMG) and including a more distinct selected patient group are needed to investigate whether muscle SWE is a valid and reliable tool for objective assessment of rigidity in PD.

Publication History

Article published online:
20 June 2022