Long latency reflexes derived from trapezius muscle and changes of these reflexes in patients with postural instability and coordination disorder

ULRs are polysynaptic reflex cycles derived from both proximal and distal muscles. ULRs provide important information about ascending tractus from cortex to beginning point of stimulus and descending tractus and cortex from cortex to the point that stimulus can be recorded. The afferent pathway of the reflex is identical with the pathway that proprioceptive inputs are transferred. These proprioceptive data are used in order to provide the postural balance in static and mobile states. With the help of these data, body muscles and other muscle activities get adjusted.The role of trapezius muscle, which belongs to body muscle subgroup, is to fix the scapula during head, neck and extremity motions. In other words, the trapezius muscle is an important proximal muscle to provide the postural balance.Neurodegenerative diseases are commonly seen in the general population and among them Parkinson?s is the leading disease. Mechanisms of postural disorders are multiple and complicated in these kind of diseases. Mostly, there are multiple causes leading to disease. Uncoordinated function between proprioceptive processing mechanisms and reflex cycles including both cortex and extra-cortex structures is one of these causes. İt?s a well-known fact that there are reflex connections between proximal and distal muscles; ULRs are one of these reflexes.In this study, we aimed to investigate the changes in trapezius muscle, an important proximal muscle providing posture adjusting via ULRs, in patients who have postural instability and to determine if these changes were significant or not. We assessed 33 Parkinson?s disease patients, 3 cerebellar degeneration patients, and 22 control cases. Postural instability was present in 13 Parkinson?s disease patients. All the cerebellar disorder patients had significant body ataxia. The clinical state of Parkinson?s disease patients were assessed by UPDRS score system. Cases were divided into two groups either having postural instability or not. All cases were assessed for peripheral nerve transmission and further electrophysiological tests applied to cases without any abnormalities. ULRs were recorded from distal thenar muscle (abductor pollicis brevis) and proximal trapezius muscles via bilateral medial nerve stimulation. Stimulation of median nevre was followed by simultaneous bilateral trapezius muscle recording, furthermore; 5 Hz TTMU was applied to the primary motor area point of thenar muscle in Parkinson?s disease patients with postural disorder. ULRs and UPDRS were recorded both before and after this test by the finger tapping test.Both our implications and data derived from statical analyses show that polysynaptic excitability is increased in Parkinson?s disease cases, reflex responses can change via changes in cortex excitability by TTMU, and cortex plays a role in reflex organization. With the comparison of ULRs derived from trapezius and thenar muscles in Parkinson?s disease patients, we hypothesized that these reflexes can trace different neural polysynaptic cycles. Some of the components of reflex responses couldn?t be obtained in Parkinson?s disease patients with postural instability, and this observation led us to the conclusion that ULR cycles are deteriorated in association with postural instability. ULRs from the trapezius muscle couldn?t be recorded in patients with cerebellar disorders. This result is not statically significant because of a small patient group, but this observation may be helpful for future studies.In conclusion: ULRs have large electrophysiological variability in patients with postural instability; however, more studies are needed to make a conclusion that other diseases with postural instability have the same kind of variability.Key Words: ULR, Trapezius muscle, Postural instability, Parkinson?s disease