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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 37  |  Issue : 4  |  Page : 164-169

Long latency reflexes in patients with postural instability and ataxia


1 Department of Neurology, Adnan Menderes University Medical Faculty, Aydin, Turkey
2 Department of Clinical Neurophysiology, Adnan Menderes University Medical Faculty, Aydin, Turkey
3 Department of Neurology and Clinical Neurophysiology, Adnan Menderes University Medical Faculty, Aydin, Turkey

Date of Submission09-Apr-2020
Date of Decision21-May-2020
Date of Acceptance15-Jun-2020
Date of Web Publication29-Dec-2020

Correspondence Address:
Cengiz Tataroğlu
Department of Neurology, Adnan Menderes University Medical Faculty, 09100 Aydin
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NSN.NSN_44_20

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  Abstract 


Objectives: Distal electrical stimulation of an upper extremity mixed nerve can generate a reflex response from the trapezius muscle. This reflex response may have a central neural pathway and can be affected by postural changes. Materials and Methods: In this study, long latency reflexes (LLRs) from both distal and trapezius muscle were evaluated in patients with Parkinson's disease (PD) with and without postural dysfunction and in patients with cerebellar ataxias. Thirty-three patients with PD, 10 patients with degenerative cerebellar ataxia and 22 healthy volunteers were included in the study. LLRs were recorded from ipsilateral thenar and trapezius muscles. Latencies and amplitudes of LLRs obtained from thenar (thenar LLR) and trapezius (trapezius LLR) muscles were analyzed. Results: In patients with PD, thenar LLRs showed significant shortening in the onset latencies and significant increase in the amplitudes in comparison with healthy controls. Trapezius LLRs did not show any significant difference in latencies or amplitudes; however, these responses showed a significant absence in one or two components in patients with Parkinson's disease with postural dysfunction. Additionally, this reflex was not recorded in patients with cerebellar ataxia. Conclusion: Trapezius LLRs can give some information regarding the physiology of neural circuits responsible for postural arrangement. Cerebellar connections may have a major role in the generation of trapezius LLRs.

Keywords: Ataxia, long latency reflexes, Parkinson's disease, postural instability, sensorimotor integration, trapezius


How to cite this article:
Deneri E, Tilek N, Çoban A, Tataroğlu C. Long latency reflexes in patients with postural instability and ataxia. Neurol Sci Neurophysiol 2020;37:164-9

How to cite this URL:
Deneri E, Tilek N, Çoban A, Tataroğlu C. Long latency reflexes in patients with postural instability and ataxia. Neurol Sci Neurophysiol [serial online] 2020 [cited 2021 Jan 19];37:164-9. Available from: http://www.nsnjournal.org/text.asp?2020/37/4/164/305388




  Introduction Top


Long duration and low intensity electrical stimulation of a peripheral nerve can generate late reflex responses from a muscle undergoing a stable voluntary contraction. These responses are known as long latency reflexes (LLRs).[1],[2] These reflexes have been studied in hand muscles.[3],[4] LLRs obtained from intrinsic hand muscles following electrical stimulation of mixed nerves have an early spinal component (HR) and three late components. It is believed that HR is a synonym of monosynaptic H reflex. The second of the late components, which is the most stable (LLR2), is recorded at about 50 ms. It is believed that this component has a transcortical generator.[3],[4],[5] These reflex responses can be accepted as an electrophysiological parameter reflecting central sensorimotor integration.

Recently, LLRs have also been recorded from axial muscles, and some features of these reflexes have been investigated.[1] Electrical stimulation of upper extremity distal mixed nerves can generate a reflex response obtained from the trapezius muscles. This reflex response includes a series of components. The first and second components have been observed more frequently and their latencies are about 30 and 50 ms, respectively. The exact central neural pathway is not known; however, postural changes can affect these reflex responses. We observed in our previous report that postural changes modified the amplitudes of these responses.[1] Therefore, it is postulated that trapezius LLRs may give some information regarding the physiology of central postural adjustments.[1]

We became interested in the behavior of these reflexes in some neurological disorders which influence central postural organization. Postural instability due to Parkinson's disease (PD) and ataxia due to cerebellar involvement are prominent conditions causing posture and gait disturbances. The mechanism of postural instability in PD is not completely understood. However, it is suggested that the pedunculopontine tegmental nucleus might play a role as an interface between the basal ganglia and the cerebellum in stabilizing posture.[6] This nucleus may also have a role in sensorimotor integration.[7]

It seems that disturbances in sensorimotor integration due to neurological disorders can contribute to the development of postural instability. LLRs may give information regarding central sensorimotor integration, and so the analysis of these reflex studies may give valuable information about the appearance of postural instability.

In this study, analyses of LLRs obtained from distal extremity muscles and axial muscles were performed in patients with PD with and without postural instability and in patients with marked cerebellar involvement. The aim was to investigate the effects of different types of postural dysfunction on these reflex responses.


  Materials and Methods Top


Thirty-three patients with PD (14 females and 19 males), 10 patients with cerebellar ataxia (6 females and 4 males) and 22 healthy volunteers (13 females and 9 males) were included in the study. The mean ages of the healthy controls and patients (patients with PD and patients with cerebellar ataxia) were 57.0 ± 7.3, 60.6 ± 6.6, and 62.3 ± 9.0 years, respectively. There was no significant age difference between groups (P > 0.05). Fourteen patients with PD had postural instability, and the patients with PD were divided into two groups in accordance with this finding. The diagnostic criteria of the Movement Disorders Society for PD were used for the diagnosis of PD.[8]

Subjects with Parkinson-plus disease, secondary Parkinsonism, or any systemic disease were excluded from the study. Tremor dominant patients were excluded because this clinical feature may cause difficulty in the stability of voluntary muscle contraction. In addition, subjects with peripheral neuropathy were also excluded from the study.

Patients with both truncal and extremity ataxias on both sides were included to the ataxia group. Patients with pyramidal, extrapyramidal, or mental involvement and dysautonomia were not included in the cerebellar ataxia group. Magnetic resonance imaging investigations disclosed pure cerebellar atrophy in these patients.

All subjects gave informed consent for the study and the study was approved by the local ethics committee.

Clinical evaluation

Unified Parkinson Disease Rating Scale (UPRDS) scores were recorded for every patient with PD. Postural stability was evaluated visually by the pull test. For this test, the individual was moderately pushed backward from the shoulders by the examiner. If the individual could not maintain an upright position, this test was considered as positive and the individual was accepted as having postural instability.[9]

Electrophysiological evaluation

Routine sensory and motor nerve conduction studies of upper and lower extremity peripheral nerves (median, ulnar, tibial, peroneal nerves, and sensory nerve conduction of the sural nerve on one side) were performed in all individuals participating to the study. All patients with PD were in the “on” period of the disease during electrophysiological investigations.

Long latency reflexes

Initially, thenar LLRs were recorded, and then trapezius LLRs were recorded. The recordings of thenar LLR were performed on the right side and then on the left side. At least two traces were recorded and superimposed for each side. The recording was performed using surface cup electrodes with the belly-tendon technique from the abductor pollicis brevis muscle. Square wave electrical pulses were delivered to the median nerve at the wrist level by a standard surface stimulating electrode. Stimulus intensity was set as the stimulus intensity causing just visible motor activity on the median innervated distal muscles. Stimulus duration was 0.5 ms. The stimulus was delivered at random, and interstimulus intervals were about 2–5 s. At least 40 traces were recorded and averaged for each recording. Filter settings were set between 10 Hz and 2 kHz. Sweep duration was 20 ms/div. During the recording, individuals were instructed to maintain a moderate stable isometric muscle contraction (50% of maximal voluntary contraction).

Trapezius LLRs were recorded from the ipsilateral trapezius. Surface cup electrodes were used for recording. An active electrode was placed on the belly of the trapezius at the midpoint between the acromion and spinous process of vertebra C7. A reference electrode was placed over the acromion.

Stimulus intensity was set at twice the motor threshold intensity determined by the recording of the thenar muscle during the analysis of the LLRs of the distal muscle. Other stimulus parameters were similar to distal LLRs. First, right side and then left side stimulations and recordings were performed. During the recording, a moderate stable isometric voluntary contraction of the trapezius was maintained. For this, individuals were instructed to make a shoulder elevation with about 50% of maximal muscle force. The stability of voluntary electromyographic activity was monitored by visual and auditory feedback during the recordings of reflex responses from both the thenar and the trapezius muscles.

Data analysis

Peak-to-peak amplitudes and onset latencies of the early spinal component (HR) and the second long latency component (LLR2) were evaluated.

In the analysis of LLRs obtained from the trapezius muscle, amplitude, and onset latencies of the first and second components were evaluated. The frequency of these components was evaluated both in the patients with PD and in the healthy controls.

Statistical analysis

Descriptive analysis of electrophysiological and clinical data was performed. The Kolmogorov–Smirnov test was used to show normal distribution of variables. Electrophysiological data obtained from patient groups and controls were compared using the one-way analysis of variance test. Homogeneity of variances was tested by post hoc test. Tukey's test was used as post hoc analysis. The Mann–Whitney U -test was used as nonparametric tests. In addition, the Chi-square test was used to test the significance of the frequency of reflex response. Possible relationships between clinical and electrophysiological data were tested by Spearman correlation analysis. P < 0.05 was considered as statistically significant.


  Results Top


Clinical evaluation

The patients with PD included in the study had a duration of the disease ranging from 1 to 35 years. All patients with PD had rigidity and bradykinesia, and 14 out of the 33 patients with PD had postural instability. Seventeen of the patients with PD also had rest tremor. All patients had an akinetic-rigid dominant clinical picture of PD. The mean UPDRS score was 28.1 ± 21.7 (4–88). In addition, the mean motor score of UPDRS was 15.8 ± 10.9 (1–47). Motor findings were markedly unilateral in eight patients with PD. The right side was slightly more affected (in five subjects).

The ataxic patients included in the study had a duration of disease which ranged from 7 to 25 years. All patients had both extremity and truncal ataxia and cerebellar dysartria (pancerebellar syndrome). Ten patients were diagnosed with hereditary cerebellar ataxia and had a family history of degenerative ataxia.

Long latency reflexes obtained from the thenar muscle

The early spinal component of thenar LLR (HR) was recorded in all individuals. Among the later components, the second component of LLR (LLR2) was the most stable. The third component was not observed clearly in any subject, and LLR1 was observed clearly in only four subjects. LLR2 was recorded in all patients with PD.

The latencies of LLR2 obtained from the patients with PD were significantly shorter than those from the healthy controls (P : 0.001). The mean amplitude of the LLR2 was also higher than in the healthy controls [Figure 1]. This difference was more marked in the right sides of the patients and healthy controls. Slight clinical asymmetry between right and left sides may cause this difference. Differences in the thenar LLRs between subgroups are shown in [Table 1].
Figure 1: Long latency reflexes obtained from the thenar muscle (a) and both trapezius muscles (b) in a patient with Parkinson's disease who had rigidity especially on his left side. The second component of the thenar long latency reflex was increased. However, long latency reflexes obtained from the trapezius did not show a significant difference

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Table 1: Differences in the thenar long latency reflexes between subgroups

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When we compared electrophysiological data between patients with and without postural dysfunction, we found no significant difference.

In patients with ataxia, thenar LLRs showed no significant difference from those of healthy controls [Table 1].

Long latency reflexes obtained from the trapezius

Mean latencies and amplitudes of trapezius LLR did not show significant difference in patients with PD. Furthermore, no significant difference was observed in these parameters between both the patients with and without postural instability and the healthy controls. [Table 2] shows the electrophysiological findings in the patients and controls.
Table 2: Electrophysiological data of long latency reflexes obtained from the trapezius muscle in patients with and without postural instability

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Trapezius LLR did not show high stability in healthy controls. Some components may be absent in some individuals. The first component of the trapezius LLR could not be recorded in six individuals (6/44). The second component of the trapezius LLR could not be recorded in nine healthy controls (9/44).

The most conspicuous abnormality of trapezius LLRs was observed in patients with ataxia. Trapezius LLRs were not recorded in any patient with prominent cerebellar dysfunction.

Some components of trapezius LLRs were absent more frequently in patients with PD. In patients with PD without postural instability, the first component of the trapezius LLR could not be recorded in seven extremities (7/38) (P > 0.05). The second component of the trapezius LLR could not be recorded in nine extremities (9/38) (P > 0.05).

In patients with PD with postural instability, the absence of the first component of the trapezius LLR was observed more frequently than in patients without postural instability (14/28 extremities, P : 0.001, χ2: 11.3). Furthermore, the absence of the second component was also observed in patients with postural instability 12/28 (P : 0.03, χ2: 4.2). These results suggest that there were significant decreases in the frequencies of trapezius LLRs in patients with PD with postural instability.

There was no significant correlation between the clinical scales and the electrophysiological data.


  Discussion Top


In the present study, LLRs elicited by electrical stimulation of the median mixed nerve from both axial and distal muscles of the upper extremity were analyzed in patients with cerebellar ataxia and in patients with PD with and without postural instability. We aimed to analyze the effects of postural dysfunction due to PD and diffuse cerebellar involvement on the trapezius and thenar LLRs. Possible effects of postural instability on the trapezius LLRs were our primary interest.

Mean amplitudes of LLR thenar and LLR trapezius showed some differences on the right and left sides in our individuals. However, these differences were not statistically significant. Slight clinical asymmetry in the patients with PD may explain partly this difference.

The trapezius as an axial muscle has an important role in postural adjustments.[10] LLRs obtained from the trapezius have recently been evaluated in various studies.[1],[9],[11] It has been observed that the trapezius muscle has some features which are different from the LLRs obtained from distal extremity muscles. These reflex responses can be influenced by postural changes.[1]

According to our results, cerebellar abnormalities had more impact on the trapezius LLRs than postural instability due to PD. LLRs obtained from distal muscles have been evaluated in a few studies in patients with cerebellar disorders. Claus et al. studied distal LLRs in patients with cerebellar dysfunction. Their patient group was not homogeneous, and patients with Friedreich's disease and focal cerebellar lesions were also included. In the cerebellar atrophy group in that study, some patients also had pyramidal dysfunction. They demonstrated an increase in the amplitudes of the third component of thenar LLR in patients with cerebellar atrophy.[12] However, later components of the reflex responses were not analyzed because it is recorded very rarely.

Disturbance in the coordination between different joints and extremities due to cerebellar dysfunction may be a reason for the missing trapezius LLRs in these patients. Our findings suggested that cerebellar connections may have a role in the generation of trapezius LLRs. The evaluation of trapezius LLR in patients with partial cerebellar involvement such as isolated hemispheric lesions or midline lesions may give additional information regarding the neural substrate of this reflex.

On the other hand, postural instability also had similar but less severe effects on trapezius LLR. This finding may be partly explained by subclinical cerebellar involvement in patients with PD.[13] However, loss of trapezius LLR was mainly observed in patients with postural instability, and degeneration of multiple neural substrates has been observed in PD. Therefore, we suggest that the analysis of trapezius LLRs in PD may give some information regarding the involvement of postural mechanisms.

The pathogenesis of postural instability is not exactly known. However, pedunculopontine nucleus cholinergic neuronal loss may have a role in the postural instability observed in PD.[14] On the other hand, this nucleus has connections with cerebellum and has a role in the integration of sensory inputs. Therefore, its involvement may be a reason for dysfunction in the sensorimotor integration and frequent loss in trapezius LLRs.

LLRs obtained from hand muscles have been studied many times previously in patients with PD.[2],[15],[16],[17] Enhanced amplitude and shortened latency of the second component of this reflex (LLR2) have also been observed previously.[18] In some studies, it was concluded that the main abnormality was increased excitability in the first component in patients with PD.[2] In our study, the LLR2 component was accepted as the most prominent waveform after HR. In some subjects with PD, the first component (LLR1) can be the more prominent waveform. In this condition, certain determination of LLR2 may be difficult, and LLR1 can be erroneously taken as LLR2. This is a limitation of our study.

The exact pathophysiological mechanism causing this finding has not yet been clarified.[16],[17],[19],[20] Increased excitability of the Group II reflex pathway may be responsible for this reflex alteration.[21],[22] Pasquereau and Turner concluded that segmental spinal circuits can be responsible for exaggeration of the long latency stretch reflex.[23] On the other hand, some studies suggest that an excessive corticospinal output and increased excitability of the primary motor cortex has been observed in PD.[24],[25],[26],[27],[28],[29]

In our patients, abnormalities in trapezius LLRs showed some discrepancies from those obtained from thenar LLRs as mentioned above. These differences between the behaviors of the reflexes suggested that the neural substrate or the generator of LLRs obtained from the trapezius is different from LLRs obtained from the distal hand muscle.

Continuation of stable muscle contraction of the trapezius can be more difficult in patients with ataxia and PD. This condition may cause a potential limitation in the evaluation of these reflex responses. Therefore, monitoring of stable voluntary muscle activity was an important issue. Voluntary activity was monitored in this study by visual and auditory feedback during electrophysiological recordings. In addition, tremor dominant patients were not included in the study.


  Conclusion Top


LLRs obtained from the trapezius muscle may reflect the physiology of central postural organization. Cerebellar connections may have a major role in the generation of this reflex. The analysis of this reflex in patients with partial cerebellar involvement may give additional information regarding its neural generator.

Acknowledgment

The authors would like to thank Mevlut Türe for statistical analysis and Alec Rylands for English revision in the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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