Pathofysiology of postural instability in patients with distal and proximal myopathy

Falling tendency in patients with myopathy is a common problem that is not only
the cause of mild or severe injuries, but also of fear of falling and therefore
a decreased activity level; the latter causing social isolation, decreased
fitness, increased cardiovascular complications and in a higher mortality.
Although epidemiologic studies implie that muscle weakness (myopathy) is
associated with falling tendency, the exact pathofysiology is unknown. Insight
in this pathofysiology would give more possibilities for treatment of falling
tendency in these patients.
Our assumption is that falls are partially caused by a decreased ability to
maintain balance during external perturbations. Especially patients with a
proximal weakness would have problems with maintaining their balance, because
hip and trunk movements are especially important during balance corrections
after external perturbations. Although ankle movements are of less importance
during correction after external perturbations, they play an important role in
stance balance. Patients with a distal weakness might have problems correcting
their balance because of their unability to correct their balance through ankle
movements. Proximal myopathy patients might fail in correcting their balance,
because trunk and hip movements are limited.

To determine the contribution of proximal or distal muscle weakness to
perturbations of stance induced by posturography.

This study is performed at the laboratorium for neuro-otology in the University
Hospital in Basel, Switserland. The subjects are tested with multidirectional
dynamic posturography and multisegmental motion analyses.
Subjects' balance is briefly measured during quiet stance with two pairs of
gyrometers and one pair of accelometers around pelvis, trunk and head.
Subsequently, the subjects are asked to stand on a moving platform that
perturbates in eight different directions (0°, 45°, 90°, 135°, 180°, 225°, 270°
en 315°). Each direction is repeated ten times in an unpredictable order and
with different intervals. Balance is measured objectively through the
forceplatform (center of mass); muscle activity during perturbations is
measured through EMG of 10 muscles. Furthermore, motion is analysed through
infrared sensors placed at 18 spots on the extremities and trunk of the
patient. During the perturbations two assistents stand next to the subject to
help in case balance is lost and subjects can grap themselves with the
handholds next to the platform. This protocol has been identically used in
several earlier studies and is therefore sufficiently validated.

Patients are screened at the out-patients clinic of Neurology, to determine the
extent of their muscle weakness and their suitability for the study.
Furthermore, subjects are asked to fill out a questionnairy according their
medical history and balance problems and to perform balance testing during
quiet stance.
Subjects come to the university hospital in Basel, Switserland. Tests will be
done on the second day and return journey is plannend on the third day of stay.
All expenses are compensated.