Paratonia is inversely correlated to premotor areas perfusion

Paratonia is defined as an inability to relax the muscles during tone assessment, resulting in participants either opposing or facilitating the examiner's movement involuntarily. This phenomenon is frequently found in patients with cognitive impairment and has been attributed to frontal lobe dysfunction, although a direct correlation has not been established. This study aimed to explore the correlation between frontal lobe function, as assessed by functional brain imaging, and paratonia, as assessed by electromyography.

Memory clinic outpatients with suspected Alzheimer's disease who were prescribed an amyloid PET scan underwent a thorough neuropsychological examination and a paratonia assessment involving surface electromyography recording of the elbow flexors and extensors. PET image acquisition started immediately after tracer injection, and the early phase perfusion amyloid PET was used as a surrogate biomarker of neuronal injury. Multiple regression analysis was performed on amyloid-positive patients to identify the correlation between paratonia and brain perfusion.

Twenty-one amyloid PET-positive participants with a median age of 72 years were diagnosed with Alzheimer's disease and included in the analysis. All participants were right-handed, and paratonia was assessed in the left arm. Whole-brain voxel-wise analysis revealed a significant inverse correlation between the total paratonia score and cortical perfusion in a cluster encompassing the superior frontal gyrus in the left hemisphere (Brodmann areas 6, 8, and 9; P < 0.006).

This study demonstrates for the first time an inverse correlation between prefrontal perfusion and paratonia. Participants with better-preserved premotor function also show less paratonia, as reflected by reduced electromyographic activation of the muscles undergoing passive mobilization.