Investigation of passive tone and viscoelasticity in neck muscles in pre-symptomatic neck flexion abnormality in Parkinson's disease: Observational study

Abstract

Background: Forward neck flexion (FNF) is a common postural abnormality in Parkinson's disease (PD), which disturbs the overall body alignment and can lead to more severe deformities through both central nervous system control and biomechanical compensation. The purpose of the current study was to investigate the biomechanical and viscoelastic properties of forward neck muscles related to FNF in individuals with PD, both with and without FNF, in comparison to age-matched individuals with normal posture. Methods: Hand-held myotonometry (Myoton Pro®) was conducted to determine the biomechanical and viscoelastic properties of the sternocleidomastoid and anterior scalene muscles of all thirty participants: individuals with PD and FNF (n = 10), individuals with PD without FNF (n = 10), and normal controls (n = 10). Result: Individuals with PD, both with and without FNF, exhibited higher passive tone and muscle stiffness and lower elasticity, relaxation time, and creep in both muscles, particularly in the sternocleidomastoid, compared to age-matched normal controls. No significant differences in any muscle variables were found between the two PD groups. Conclusion: These findings indicate that the biomechanical and viscoelastic properties of neck muscles are altered even in the presymptomatic stage of postural abnormalities in PD. This may provide potential evidence of underlying peripheral factors that involve postural deformities via proprioceptive disturbances and exacerbate rigidity in PD.