Posture impairments in amyotrophic lateral sclerosis (ALS) are linked to deficits in trunk control and in the mechanisms that control the body’s response to surface tilts. Moreover, these abnormalities also correlated to disease severity.
Those findings are in the study “Abnormal trunk control determines postural abnormalities in Amyotrophic Lateral Sclerosis,” which was published recently in NeuroRehabilitation.
ALS is a progressive neurodegenerative disorder caused by the gradual destruction of motor neurons — nerve cells responsible for voluntary muscle control — in the spinal cord and in the brain.
“Postural instability in ALS occurs at an early stage of the disease and often results in falls, leading to premature immobility and loss of autonomy, and consequently to an impaired quality of life. It was frequently assumed that balance problems are mainly related to muscle weakness of the lower limbs,” the investigators wrote.
However, more recently, scientists have proposed a series of other mechanisms that may be involved in posture impairments, such as muscle tightness (spasticity), and perturbations in the vestibular or extrapyramidal systems. These systems are responsible for controlling body balance and involuntary muscle movements, respectively.
“However, [in the context of ALS,] the contribution of the different [motor and sensory] systems and their central processing to postural instability has not been identified yet,” they noted.
A group of researchers from the University Medical Center of Freiburg (Germany) set out to discover the mechanisms involved in the loss of postural control in ALS, as well as their relationship with clinical features of disease severity.
Postural control was examined using a custom-built motion platform, on which participants were asked to stand upright with their feet planted in a marked area. The platform was used to measure both spontaneous body sway movements and body movements that occurred in response to platform tilting, while participants had their eyes opened or closed.
Spontaneous sway movements were repeated twice, whereas perturbed stance tests were repeated eight times. Test results were correlated to clinical test scores of disease severity, including the ALS Functional Rating Scale (ALSFRS), the 10 meter walking test (10MWT), timed up and go test (TUG) and the short-form 36 health survey (SF-36).
The study enrolled 12 ALS patients and 12 age-matched healthy individuals (controls).
Results showed that spontaneous body sways were wider, faster, and more frequent among ALS patients compared to healthy individuals.
In addition, researchers found that ALS patients had weaker responses to platform tilting compared to controls. Moreover, during the tilting test in which participants were asked to keep their eyes closed, ALS patients had excessive upper body movements compared to healthy subjects.
“This indicates a different axial body control in ALS, as has already been examined in ALS patients with neck weakness. However, we deem it unlikely that this abnormal axial control is solely attributable to muscle weakness since it vanishes with open eyes. Instead, we suggest that ALS patients display a different central control strategy,” they explained.
Finally, investigators found that posture impairments observed in ALS patients were strongly correlated, either directly or indirectly, with scores of clinical tests assessing motor function and balance (e.g., ALSFRS, TUG, 10MWT).
“We conclude that ALS patients’ postural abnormalities are mainly determined by an abnormal axial control and abnormally small body excursions [movements] as a function of support surface tilts, seemingly indicating better postural stabilization than control subjects,” the researchers wrote.
“These postural abnormalities closely correlate with clinical parameters and, therefore, may function as a sensitive indicator for ALS disease severity. As a therapeutic consequence, therapy for ALS patients should incorporate postural training with a focus on axial control,” they added.
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