Freedom of Movement May Be Misinterpreted as Balance Instability, Parkinson’s Study Suggests
Antiparkinsonian medicines may allow patients with mild to moderate Parkinson’s disease to experience freedom of movement, which could be confused with balance issues if measured by traditional postural stability testing, researchers suggest.
Their findings were published in the study, “The influence of dopaminergic medication on balance automaticity in Parkinson’s disease,” in the journal Gait & Posture.
Dopaminergic medications can help control Parkinson’s motor symptoms, but as the disease progresses, patients typically need to gradually increase the treatment dose for maximum benefit. Even after increasing the dose, they might sometimes experience a reappearance or worsening of symptoms (off periods) due to the diminishing effects of the therapy.
It is known that Parkinson’s patients have difficulty performing learned motor skills automatically, a phenomenon referred to as decreased motor automaticity. Automaticity is the ability to perform movements without having to pay attention to the details of the movement, particularly for actions that require low levels of precision or for movements that are frequently made.
Studies also report that the ability to perform two or more tasks at the same time, called dual-tasking, is impaired in Parkinson’s disease.
“Dual-tasking involves performing a primary motor task (e.g., standing) and a secondary task (e.g., conversing) simultaneously and is the primary means of assessing the automaticity of a given motor task,” the researchers wrote.
In theory, if a primary task is automatic, performing another task simultaneously should not interfere with the first one.
Although dopaminergic medication seems to improve dynamic balance (the ability to maintain postural stability while in motion), there is still little evidence on how it influences standing balance (the ability to maintain the body in a fixed posture).
University of Houston researchers set out to evaluate how dopaminergic medication influenced long-duration standing balance with the eyes open or closed while dual-tasking in Parkinson’s disease.
They recruited 16 Parkinson’s patients with mild to moderate disease (four women and 12 men, with a mean age of 67.1 years) for the study.
Before dual-task testing, the participants underwent a minimum 12-hour overnight medication withdrawal, so that researchers could assess patients’ status in an off state.
Single- and dual-task tests were conducted. For dual-task testing, patients had to stand in silence (primary task), both with their eyes open and then with them closed, while listening on headphones to a pre-recorded unfamiliar speech and mentally counting the number of times a specific word occurred (secondary task). This is known as phoneme monitoring. They also had to listen to the details of the story so that they could answer a few questions about it at the end of the testing session.
Under the protocol, participants were asked to perform the following tasks in random order: 1) phoneme monitoring while seated comfortably in a quiet room, 2) single-task standing eyes open, 3) single-task standing eyes closed, 4) dual-task standing eyes open, and 5) dual-task standing eyes closed.
“After the [off] trials were completed, the subjects took their dopaminergic medication as prescribed for their first/morning dose and waited until they achieved a stable ‘on’ feeling (minimum of 45 [minutes]) before commencing the on-medication testing,” the researchers said.
Every trial session was performed once for three minutes, and participants were given at least a minute between sessions to sit down and rest.
Data on motor variables of interest were obtained by the NeuroCom Balance Master, a system that uses a fixed force plate to measure the vertical forces exerted through the patient’s feet to measure the center of gravity position and postural control.
Results revealed that antiparkinsonian medicines significantly increased center of pressure movement. The center of pressure is a point, inside or outside the body, where the resulting vector of all forces (including gravity) acting on the body is considered to act.
Patients’ performance in the secondary task was reduced after they took the medications.
Additionally, having the eyes closed or open significantly increased the patients’ back and forth plus lateral sway velocities and the integrated time to boundary.
In biomechanics, time to boundary estimates the time required for the center of pressure to reach the boundary of the base of support if it were to continue its instantaneous trajectory and velocity. Higher integrated time indicates poorer balance.
Postural sway was also increased during the on state. Scientists often interpret increases in sway velocity and integrated time to boundary as indications of impaired balance; however, the researchers suggest that their findings could indicate an increase in freedom of movement rather than compromised stability.
Importantly, medication did not improve balance automaticity.
“The data did not support a medication-induced improvement in automaticity, as measured by significant medication by task interactions. An alternate interpretation for medication-induced balance changes in PD [Parkinson’s disease] includes an increase in maneuverability without sacrificing stability after taking dopaminergic medication,” the researchers concluded.