P 40 Muscle ultrasound in idiopathic Parkinson's disease with deep brain stimulation: Rigidity can be quantified by shear wave elastography

Abstract

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 ultrasound shear wave elastography (SWE): Here, tissue elasticity (simply speaking, stiffness) can be estimated non-invasively measuring the propagation speed of sonic waves through biological tissue. Since rigidity is basically an increased stiffness of the muscles, it seems reasonable to investigate whether the increased muscle rigidity in PD can be quantified using SWE of the muscles. Methods In a proof-of-principle study of 10 PD patients and 10 healthy controls, shear wave velocity (SWV) was measured bilaterally at the biceps brachii muscle and flexor digitizing profundus muscle in rest and passive stretch in 5-minute-intervals longitudinally over a total period of 80 minutes. Half of PD patients were treated invasively with deep brain stimulation (DBS) and the other half conservatively with levodopa. In patients, UPDRS-III was additionally evaluated. To provoke a change of muscle rigidity, in a fixed protocol DBS was turned on and off and levodopa was administered. Results At group level, the overall SWV 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 revealed, 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. Conclusions Muscle ultrasound SWE - as a proof-of-principle - might potentially be 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.