Clinical dissociation and electromyographic convergence of paratonia in cognitive impairment including Alzheimer's disease: Evidence for a shared central inhibitory mechanism.

BackgroundDespite a shared conceptual framework linking both components to impaired inhibitory control, clinical evidence suggests that facilitatory and oppositional paratonia are not equally related to cognitive deterioration, with facilitatory paratonia showing a stronger association with cognitive impairment. Whether this apparent divergence reflects true neurophysiological differences or arises from limitations intrinsic to clinical assessment remains unclear. Electromyography (EMG)-based assessment offers a direct approach to quantify involuntary muscle activation and reduce measurement-related confounding factors.ObjectiveTo determine whether the reported clinical divergence between facilitatory and oppositional paratonia reflects distinct neurophysiological mechanisms or is primarily driven by measurement-related factors.MethodsEighty-six participants (46 cognitively impaired and 40 cognitively healthy) underwent clinical and EMG-based assessment of paratonia during passive elbow movements. Associations with global cognitive status (Mini-Mental State Examination) and discriminative performance between cognitively impaired and healthy subjects were evaluated.ResultsClinically assessed facilitatory paratonia showed stronger associations with cognitive status and better discriminative performance than oppositional paratonia. In contrast, EMG-based assessment revealed comparable associations with cognitive status and similar discriminative performance for both paratonia components.ConclusionsEMG assessment reveals a neurophysiological convergence between facilitatory and oppositional paratonia, supporting a shared central inhibitory mechanism. Our findings indicate that the apparent clinical distinction between facilitatory and oppositional paratonia does not reflect a true pathophysiological separation, but is largely driven by limitations inherent to clinical assessment. In this context, facilitatory paratonia emerges as the most informative bedside marker of cognitive impairment.