Postural instability in Parkinson's disease assessed by instrumented pull-test: Clinical-pharmacological implications

Postural Instability (PI) in Parkinson's Disease (PD) and its responsiveness to Levodopa (LD) have been poorly investigated quantitatively. Primary outcomes of the study were to quantify postural instability in a cohort of LD-treated PD patients in order to reliably discriminate stable from unstable PD subjects and to detect acute response to LD on PI.

We enrolled N = 28 patients diagnosed with "clinically definite" PD. Two groups were identified according to the score of the "postural instability" MDS-UPDRS item: 15 PD with Postural Stability (PD-PS) and 13 PD with PI. Each patient performed an "instrumented pull-test" five times both in OFF and in ON state, wearing a passive marker on the sternum. Marker positions were recorded by an optokinetic system. "Total Time" (TT) was estimated for all patients, indicating time from the onset of postural change until recovery. Healthy Controls (HC) data were used as reference.

TT values were significantly different when comparing HC to PD and PD-PS to PD-PI. Significant differences were also found when comparing TT values among "stable" vs "unstable" trials, as well as when comparing TT values before and after LD administration. TT threshold equal to 3.64s discriminated between stable and unstable trials with an accuracy of 83.2 %.

TT may represent a reliable biomarker of PI in PD, resulting modified by LD. Study results highlight dopaminergic mechanisms underlying PI in PD.