Clinical and electromyographic examinations of Parkinsonian tremor

Investigation of Phase Shifts Using AUC Diagrams: Application to Differential Diagnosis of Parkinson's Disease and Essential Tremor

This study was motivated by the well-known problem of the differential diagnosis of Parkinson's disease and essential tremor using the phase shift between the tremor signals in the antagonist muscles of patients. Different phase shifts are typical for different diseases; however, it remains unclear how this parameter can be used for clinical diagnosis. Neurophysiological papers have reported different estimations of the accuracy of this parameter, which varies from insufficient to 100%. To address this issue, we developed special types of area under the ROC curve (AUC) diagrams and used them to analyze the phase shift. Different phase estimations, including the Hilbert instantaneous phase and the cross-wavelet spectrum mean phase, were applied. The results of the investigation of the clinical data revealed several regularities with opposite directions in the phase shift of the electromyographic signals in patients with Parkinson's disease and essential tremor. The detected regularities provide insights into the contradictory results reported in the literature. Moreover, the developed AUC diagrams show the potential for the investigation of neurodegenerative diseases related to the hyperkinetic movements of the extremities and the creation of high-accuracy methods of clinical diagnosis.

Re-emergent Tremor in Parkinson's Disease: The Role of the Motor Cortex

BACKGROUND

Parkinson's disease patients may show a tremor that appears after a variable delay while the arms are kept outstretched (re-emergent tremor). The objectives of this study were to investigate re-emergent tremor pathophysiology by studying the role of the primary motor cortex in this tremor and making a comparison with rest tremor.

METHODS

We enrolled 10 Parkinson's disease patients with both re-emergent and rest tremor. Tremor was assessed by spectral analysis, corticomuscular coherence and tremor-resetting produced by transcranial magnetic stimulation over the primary motor cortex. We also recorded transcranial magnetic stimulation-evoked potentials generated by motor cortex stimulation during rest tremor, tremor suppression during wrist extension, and re-emergent tremor. Spectral analysis, corticomuscular coherence, and tremor resetting were compared between re-emergent tremor and rest tremor.

RESULTS

Re-emergent tremor showed significant corticomuscular coherence, causal relation between motor cortex activity and tremor muscle and tremor resetting. The P60 component of transcranial magnetic stimulation-evoked potentials reduced in amplitude during tremor suppression, recovered before re-emergent tremor, was facilitated at re-emergent tremor onset, and returned to values similar to those of rest tremor during re-emergent tremor. Compared with rest tremor, re-emergent tremor showed similar corticomuscular coherence and tremor resetting, but slightly higher frequency.

CONCLUSIONS

Re-emergent tremor is causally related with the activity of the primary motor cortex, which is likely a convergence node in the network that generates re-emergent tremor. Re-emergent tremor and rest tremor share common pathophysiological mechanisms in which the motor cortex plays a crucial role. © 2020 International Parkinson and Movement Disorder Society.

Latency of re-emergent tremor in Parkinson's disease is influenced by levodopa

INTRODUCTION

Re-emergent tremor (RET) is a common form of postural tremor observed in Parkinson's disease (PD) patients. Recent studies have shown that administration of levodopa decreases RET amplitude. However, drug effects on tremor pause duration are less clear.

METHODS

We performed a prospective observational study in PD patients with RET, subjected to acute levodopa challenge. Tremor activity was measured during OFF and ON states both clinically, as well as by using accelerometers taped to the back of both hands. Correlation between RET amplitude and pause duration, as well with MDS-UPDRS scores were investigated. The slope of gradual increase of postural tremor after the pause was also measured in the OFF and ON states.

RESULTS

Significant inverse correlation between tremor amplitude and RET pause duration was observed in OFF (rs = -0.474, p = 0.030) and ON (rs = -0.569, p = 0.006) states. Levodopa reduced tremor amplitude (26%, p = 0.004) dampening slope gradient (22%, p = 0.029). Tremor pause duration also showed inverse correlation with postural tremor amplitude measured by MDS-UPDRS in OFF (rs = -0.311, p = 0.048) and ON (rs = -0.503, p = 0.020) states, as well as with total MDS-UPDRS Part III score (rs = -0.295, p = 0.009). Finally, accelerometric analysis proved to be more sensitive than visual inspection for detecting tremor pauses.

CONCLUSION

Our results suggest RET pause duration is amplitude related, since levodopa-induced amplitude decrease led to pause prolongation, associated with decreased tremor intensity and slope gradient dampening.

Re-emergent tremor in Parkinson's disease

INTRODUCTION

Re-emergent tremor (RET) is a postural tremor that appears after a variable delay in patients with Parkinson's disease (PD). The aim of the present study was to evaluate the occurrence and the clinical characteristics of RET in a population of patients with PD.

METHODS

We consecutively assessed 210 patients with PD. We collected the patients' demographic and clinical data. RET was clinically characterized in terms of latency, severity and body side affected. We also investigated a possible relationship with motor and non-motor symptoms and differences in the clinical features in patients with and without RET.

RESULTS

RET was present in 42/210 patients. The mean latency of RET was 9.20 ± 6.8 seconds. Mean severity was 2.4 ± 1.9. RET was unilateral in 21 patients. Patients with RET had less severe speech, posture and gait disorders and upper limb and global bradykinesia than patients without RET. Similar findings were observed when we compared patients with RET with patients with tremor at rest associated with action tremor, patients with isolated action tremor and patients with no tremor. By contrast, patients with RET tremor did not clinically differ from those with isolated tremor at rest.

CONCLUSION

Our results suggest that patients with RET and patients with isolated tremor at rest represent the same clinical subtype, whereas patients with action tremor (whether isolated or associated with tremor at rest) might belong to a distinct subtype that is clinically worse. Patients with RET represents a benign subtype of PD, even within the tremor-dominant phenotype.

Re-emergent tremor in Parkinson's disease: A clinical and electromyographic study

BACKGROUND

Re-emergent tremor (ReT) in Parkinson's disease (PD) is the tremor that re-emerges after a variable period of latency while maintaining posture. The phenomenology and electrophysiological aspects of ReT have not been well characterized. The aims of this study were to characterize ReT clinically and electrophysiologically.

METHODS

Sixty three patients with tremor dominant PD were recruited and subjected to clinical and electrophysiological evaluations. Group 1 consisted of 26 patients with rest tremor (RT) and ReT and group 2 consisted of 37 patients with RT and postural tremor (PT). The presence of silent period of ReT was determined clinically and confirmed electrophysiologically.

RESULTS

The duration of illness was significantly shorter in patients with ReT as compared to patients without ReT (5.2±4.4years vs 7.4±4.5years, p=0.03). ReT was similar to RT in terms of both frequency (4.8±0.7Hz vs 4.7±0.6Hz, p=0.1) and pattern of contraction. The frequency of RT was not significantly different in the 2 groups (p=0.5). The mean duration of silent period was 8.1±8.7s.

CONCLUSIONS

A significantly shorter duration of illness was found in patients with ReT as compared to patients without ReT. ReT is similar to RT in terms of frequency and pattern of contraction. However, the presence of silent period may imply additional pathophysiological mechanisms.

Action tremor in Parkinson's disease: frequency and relationship to motor and non-motor signs

BACKGROUND AND PURPOSE

Action tremor may occur in patients with Parkinson's disease and cause misdiagnosis with other movement disorders such as essential tremor and dystonia. Data on the frequency of action tremor in Parkinson's disease and on the relationships with other motor and non-motor signs are limited.

METHODS

A cross-sectional study of 237 patients with Parkinson's disease staging 1-2 on the Hoehn-Yahr scale was conducted. Data on action tremor and other motor and non-motor signs were collected using the Unified Parkinson's Disease Rating Scale part III and the Non-Motor Symptoms Scale.

RESULTS

Action tremor was found in 46% of patients and was associated with both severity of rest tremor (adjusted odds ratio 3.0, P < 0.001) and severity of rigidity (adjusted odds ratio 1.5, P = 0.004). No association was found between action tremor and severity of bradykinesia (adjusted odds ratio 0.97, P = 0.4) or axial symptoms (adjusted odds ratio 0.9, P = 0.3). Moreover, patients who had action tremor reported a significant lower mean number of non-motor symptoms than those who had not (2.1 ± 1.3 vs. 2.4 ± 1.3; P = 0.04).

CONCLUSIONS

Action tremor is a relatively frequent motor sign in patients with Parkinson's disease staging 1-2 on the Hoehn-Yahr scale. Action tremor correlates with rest tremor and rigidity and may be associated with a lower burden of non-motor symptoms. These findings suggest a contribution of non-dopaminergic mechanisms to action tremor pathophysiology.

Electrophysiologic characteristics of tremor in Parkinson's disease and essential tremor

Tremor in essential tremor (ET) and Parkinson's disease (PD) usually present specific electrophysiologic profiles, however amplitude and frequency may have wide variations.

OBJECTIVE

To present the electrophysiologic findings in PD and ET.

METHOD

Patients were assessed at rest, with posture and action. Seventeen patients with ET and 62 with PD were included. PD cases were clustered into three groups: predominant rest tremor; tremor with similar intensity at rest, posture and during kinetic task; and predominant kinetic tremor.

RESULTS

Patients with PD presented tremors with average frequency of 5.29±1.18 Hz at rest, 5.79±1.39 Hz with posture and 6.48±1.34 Hz with the kinetic task. Tremor in ET presented with an average frequency of 5.97±1.1 Hz at rest, 6.18±1 Hz with posture and 6.53±1.2 Hz with kinetic task. Seven (41.2%) also showed rest tremor.

CONCLUSION

The tremor analysis alone using the methodology described here, is not sufficient to differentiate tremor in ET and PD.

Distinguishing essential tremor from Parkinson's disease: bedside tests and laboratory evaluations

Distinguishing essential tremor from Parkinson's disease can be challenging, both in the early stages of these diseases and as these diseases progress. Various tremor types (rest, postural, kinetic and intention) may be seen in both essential tremor and Parkinson's disease. Furthermore, with time, the two diseases may coexist within a single patient. Detailed clinical examination with attention to specific features of tremor (frequency, amplitude, pattern and distribution) and associated neurological findings may help distinguish patients with the two diseases. Laboratory testing may provide information that further aids in differentiating the two diseases. These tests include accelerometry and surface electromyography, spiral analysis, dopamine transporter imaging, olfactory testing and, eventually, postmortem histopathology. These tests have limitations and their diagnostic utility requires additional study.

Cortical correlates of the basic and first harmonic frequency of Parkinsonian tremor

OBJECTIVE

It has been hypothesized that the basic and first harmonic frequency of Parkinsonian tremor are somewhat independent oscillations the biological basis of which remains unclear.

METHODS

We recorded 64-channel EEG in parallel with EMG of the forearm muscles most affected by rest tremor in 21 PD patients. EMG power spectrum, corticomuscular coherence spectra and EEG power spectra for each EEG electrode were calculated. The dynamics of the coherence and relative EMG and EEG power at the basic (tremor) frequency were calculated by a sliding, overlapping window analysis. Corticomuscular delays and direction of interaction were analysed by the maximizing coherence method for narrow band signals.

RESULTS

The contralateral EEG electrodes with maximal coherence were different for the basic and first harmonic frequency. The dynamical coherence curves showed non-parallel time courses for the two frequencies. The mean EEG-EMG and EMG-EEG delays were all around 15-20ms but significantly longer for the first harmonic than for the basic frequency.

CONCLUSIONS

Our data indicate different cortical representations and corticomuscular interaction of the basic and first harmonic frequencies of Parkinsonian tremor.

SIGNIFICANCE

Separate central generators seem to contribute to the tremor via different pathways. Further studies on this complex tremor network are warranted.