Electrophysiological evaluation of psychogenic movement disorders

doi:10.1016/j.parkreldis.2015.09.016

Parkinsonism & Related Disorders

Volume 22, Supplement 1, January 2016, Pages S153-S158

https://doi.org/10.1016/j.parkreldis.2015.09.016 Get rights and content

Highlights

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Psychogenic movement disorders (PMD) commonly include tremor, myoclonus and dystonia.
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Diagnosis of PMD is often a challenge to neurologist and psychiatrist.
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Electrophysiology can be an useful tool to support a clinical diagnosis of PMD.
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Electrophysiology includes accelerometry, multichannel surface EMG, Jerk-locked-back averaging, etc.
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Electrophysiology may be less useful in long standing PMD and patients with mixed organic and functional movement disorders.

Abstract

Psychogenic movement disorders (PMD) include a group of neurological symptoms which cannot be explained by any organic syndrome. The diagnosis of PMD is challenging for both neurologist and psychiatrist. Electrophysiological examination is a useful tool to evaluate and support a diagnosis PMD. It includes a set of tests which are chosen appropriate to the clinical setting that provides objective criteria for the diagnosis of PMD. The various tests available include accelerometry, surface electromyography, electroencephalography, jerk locked back averaging and pre-movement potentials, somatosensory evoked potentials, transcranial magnetic stimulation (TMS) etc. Electrophysiologically psychogenic tremors display features of variability, entrainability, coactivation, distractibility and increase in the amplitude and frequency on mass loading. Movement related cortical potentials such as Bereitschaftspotential is seen in psychogenic myoclonus. Presence of triphasic contraction of muscles and absence of co-contraction suggests psychogenic myoclonus. Latency of C-reflex is longer in psychogenic myoclonus as compared to organic myoclonus. The role of TMS to differentiate psychogenic from organic dystonia is still not clear. In conclusion, electrophysiological tests are most useful for tremor, followed by jerks and least for dystonia. In patients with long-standing PMD or those with mixed pathology, electrophysiological tests may not be very useful.

Introduction

Psychogenic movement disorders (PMD) include a group of neurological symptoms which cannot be explained by any organic disorder and have an underlying psychological or psychiatric basis in majority of the patients [1]. The most common psychogenic movement disorders seen in specialist clinic are tremor, myoclonus and dystonia [2]. The clinical features which point to a diagnosis of PMD include abrupt onset, deliberate slowness of movements, bizarre or difficult to classify movements, changing characteristics of movements, presence of multiple movement disorders, excessive startle response, paroxysmal movement disorders, motor manifestations incongruous with the organic pathology and functional disability out of proportion to examination findings. These abnormal movements are variable, distractible, changing to suggestions and can be entrained [3]. The diagnosis of PMD is challenging for both the neurologist and psychiatrist. Electrophysiological examination is a useful tool to evaluate and support a diagnosis PMD. It includes a set of tests which are chosen appropriate to the clinical setting that provides objective criteria for the diagnosis of PMD [4] [Table 1]. The clinical classification of Fahn and Williams is most widely used for the diagnosis of PMD [5]. The diagnostic criteria were revised and electrophysiological criteria were included to increase the diagnostic accuracy [2].

The present review focuses on the electrophysiological methods and its role in the diagnosis of PMD.

Section snippets

Psychogenic tremor

Psychogenic tremor is often highly variable both in frequency and amplitude [6]. It tends to be present at rest, posture and during action. It can be difficult to distinguish from organic tremors such as exaggerated physiological tremors, essential tremors, parkinsonian tremors and dystonic tremors. Surface electromyography (EMG) from different muscles and accelerometry are useful electrophysiological tests to differentiate psychogenic from organic tremors. Among the two, accelerometry is best

Psychogenic myoclonus

Psychogenic myoclonus can present spontaneously or can be produced by action or by reflex. It may be difficult for the human eye to judge the latency of reflex myoclonus in which case electrophysiology is helpful. Electrophysiologically the psychogenic myoclonus is assessed by surface EMG, conventional EEG, Jerk-Locked-Back-Averaging (JLBA), somato-sensory evoked potentials (SEP), and C-reflex studies [2], [4].

Psychogenic dystonia

Psychogenic dystonia is a much less understood condition [3]. Clinically it is often difficult to decide whether a patient has psychogenic or organic dystonia. It is also difficult to perform electrophysiological tests in these patients as the muscles are not relaxed. The electrophysiological tests for psychogenic dystonias consist of multichannel surface EMG recording of the involved muscle groups and transcranial magnetic stimulation (TMS).

Psychogenic parkinsonism

Psychogenic parkinsonism is uncommon and like true parkinsonism, these patients can present in two forms – tremor predominant and akinetic–rigid form [26]. Electrophysiological studies have shown variability in frequency and amplitudes of tremors, positive entrainment and paradoxical increase in the tremor amplitude on mass loading in patients with psychogenic parkinsonism [2], [11].

Psychogenic gait disorder

Psychogenic gait disorders can manifest in different types that includes slow gait, cautious gait, bizarre gait which is difficult to classify, dystonic gait, buckling at knee, astasia-abasia [27]. Majority of these patients do not fall. Although psychogenic gait is relatively common electrophysiological studies are sparse. Patients misdiagnosed as psychogenic tremors of lower limbs on evaluation show fast rhythmic activity (14–18) Hz characteristic of orthostatic tremor [4].

Psychogenic tics

Tics are usually preceded by premonitory sensations in the form of tingling, muscle tension within the body part. These premonitory sensations are relieved by the appearance of the tic.

In one study, EEG changes in patients with simple tics were compared to the EEG changes in the same patients when they voluntarily mimicked their tics. A pre-movement potential was observed about 500 ms prior to the EMG activity when patients performed the tics voluntarily, whereas it was absent when the tics

Psychogenic palatal tremor

Palatal tremor or myoclonus refers to a group of disorders with abnormal rhythmic contractions of soft palate. Palatal myoclonus is classified into two types, essential and symptomatic.

It is believed that some patients with essential palatal tremors may have psychogenic basis.

In a study involving 10 essential palatal tremor, 7 were identified as psychogenic. These patients showed features of variability, distractibility and entrainability [29]. In addition most patients had ear clicking,

Limitations

In patients with bilateral psychogenic tremors it is difficult to demonstrate distractibility, entrainability. Also these patients may be able to maintain tremors in both limbs of different frequencies that suggest other mechanisms involved in the generation of tremors. The electrophysiological findings in patients with organic or psychogenic propriospinal myoclonus may be similar and may be difficult to differentiate [17], [21]. Presence of BP suggests psychogenic myoclonus, however it may

Conclusions

In conclusion, PMD is an important clinical problem and requires extensive and repeated evaluations. Electrophysiological testing may be helpful in characterizing the PMDs thereby preventing misdiagnosis of both organic and psychogenic movement disorders, and starting early and appropriate management [Fig. 2]. However it should be mentioned that organic and psychogenic movement disorders may co-exist where the role of electrophysiology may not be that clear.

Financial disclosure/conflict of interest

None of the authors have any financial disclosure to make or have any conflict of interest.

Source of funding

Nil.

Acknowledgment

Nil.

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