Tabish A. Saifee

Moving toward "laboratory-supported" criteria for psychogenic tremor.

A confident clinical diagnosis of psychogenic tremor is often possible, but, in some cases, a “laboratory‐supported” level of certainty would aid in early positive diagnosis. Various electrophysiological tests have been suggested to identify patients with psychogenic tremor, but their diagnostic reliability has never been assessed “head to head” nor compared to forms of organic tremor other than essential tremor or PD. We compared baseline tremor characteristics (e.g., frequency and amplitude) as well as electrophysiological tests previously reported to distinguish psychogenic and organic tremor in a cohort of 13 patients with psychogenic tremor and 25 patients with organic tremor, the latter including PD, essential‐, dystonic‐, and neuropathic tremors. We assessed between‐group differences and calculated sensitivity and specificity for each test. A number of tests, including entrainment or frequency changes with tapping, pause of tremor during contralateral ballistic movements, increase in tremor amplitude with loading, presence of coherence, and tonic coactivation at tremor onset, revealed significant differences on a group level, but there was no single test with adequate sensitivity and specificity for separating the groups (33%–77% and 84%–100%, respectively). However, a combination of electrophysiological tests was able to distinguish psychogenic and organic tremor with excellent sensitivity and specificity. A laboratory‐supported level of diagnostic certainty in psychogenic tremor is likely to require a battery of electrophysiological tests to provide sufficient specificity and sensitivity. Our data suggest such a battery that, if supported in a prospective study, may form the basis of laboratory‐supported criteria for the diagnosis of psychogenic tremor.

Believing is perceiving: mismatch between self-report and actigraphy in psychogenic tremor

We assessed the duration and severity of tremor in a real-life ambulatory setting in patients with psychogenic and organic tremor by actigraphy, and compared this with self-reports of tremor over the same period. Ten participants with psychogenic tremor and eight with organic tremor, diagnosed using standardized clinical criteria, were studied. In an explicit design, participants were asked to wear a small actigraph capable of continuously monitoring tremor duration and intensity for 5 days while keeping a diary of their estimates of tremor duration during the same period. Eight patients with psychogenic tremor and all patients with organic tremor completed the study. Psychogenic patients reported significantly more of the waking day with tremor compared with patients with organic tremor (83.5 ± 14.0% of the waking day versus 58.0 ± 19.0% of the waking day; P < 0.01), despite having almost no tremor recorded by actigraphy (3.9 ± 3.7% of the waking day versus 24.8 ± 7.7% of the waking day; P = 0.001). Patients with organic tremor reported 28% more tremor than actigraphy recordings, whereas patients with psychogenic tremor reported 65% more tremor than actigraphy. These data demonstrate that patients with psychogenic tremor fail to accurately perceive that they do not have tremor most of the day. The explicit study design we employed does not support the hypothesis that these patients are malingering. We discuss how these data can be understood within models of active inference in the brain to provide a neurobiological framework for understanding the mechanism of psychogenic tremor.

Physical precipitating factors in functional movement disorders

BACKGROUND A traditional explanation for functional (psychogenic) neurological symptoms, including functional movement disorders (FMD), is that psychological stressors lead to unconsciously produced physical symptoms. However, psychological stressors can be identified in only a proportion of patients. Patients commonly reported a physical event at onset of functional symptoms. In this study, we aim to systematically describe physical events and surrounding circumstances which occur at the onset of FMD and discuss their potential role in generation of functional symptoms. METHODS We recruited 50 consecutive patients from a specialized functional movement disorders clinic. Semi-structured interviews provided a retrospective account of the circumstances in the 3 months prior to onset of the FMD. Questionnaires to assess mood disturbance and life events were also completed. RESULTS Eleven males and 39 females were recruited. Forty (80%) patients reported a physical event shortly preceding the onset of the FMD. The FMD occurred after an injury in 11 patients and after an infection in 9. Neurological disorders (n=8), pain (n=4), drug reactions (n=3), surgery (n=3) and vasovagal syncope (n=2) also preceded the onset of the functional motor symptom. 38% of patients fulfilled criteria for a panic attack in association with the physical event. CONCLUSIONS In our cohort, physical events precede the onset of functional symptoms in most patients with FMD. Although historically neglected in favour of pure psychological explanation, they may play an important role in symptoms development by providing initial sensory data, which along with psychological factors such as panic, might drive subsequent FMD.

Rest and other types of tremor in adult-onset primary dystonia

Introduction Knowledge regarding tremor prevalence and phenomenology in patients with adult-onset primary dystonia is limited. Dystonic tremor is presumably under-reported, and we aimed to assess the prevalence and the clinical correlates of tremor in patients with adult-onset primary dystonia. Methods We enrolled 473 consecutive patients with different types of adult-onset primary dystonia. They were assessed for presence of head tremor and arm tremor (rest, postural and kinetic). Results A total of 262 patients (55.4%) were tremulous: 196 patients presented head tremor, 140 patients presented arm tremor and 98 of them had a combination of head and arm tremor. Of the 140 patients with arm tremor, all presented postural tremor, 103 patients (73.6%) presented also a kinetic component, whereas 57 patients (40.7%) had rest tremor. Rest tremor was unilateral/asymmetric in up to 92.9% of them. Patients with segmental and multifocal dystonia were more likely tremulous than patients with focal dystonia. Dystonic symptoms involving the neck were more frequently observed in patients with head tremor, whereas dystonic symptoms involving the arms were more frequently observed in patients with arm tremor. Discussion Here we show that tremor is a common feature of patients with adult-onset primary dystonia. It may involve different body segments, with the head being the most commonly affected site. Arm tremor is also frequent (postural>kinetic>rest), occurring in up to one-third of cases. There is a suggestion of a stronger tendency for spread of dystonic features in patients with associated tremor. Dystonic tremor is under-reported and this underscores the importance of careful clinical examination when assessing tremulous patients without overt dystonia.

Failure of explicit movement control in patients with functional motor symptoms

Functional neurological symptoms are one of the most common conditions observed in neurological practice, but understanding of their underlying neurobiology is poor. Historic psychological models, based on the concept of conversion of emotional trauma into physical symptoms, have not been implemented neurobiologically, and are not generally supported by epidemiological studies. In contrast, there are robust clinical procedures that positively distinguish between organic and functional motor signs that rely primarily on distracting attention away from movement or accessing it covertly. We aimed to investigate the neurobiological principles underpinning these techniques and implications for understanding functional symptoms. We assessed 11 patients with functional motor symptoms and 11 healthy controls in three experimental set‐ups, where voluntary movements were made either with full explicit control or could additionally be influenced automatically by factors of which participants were much less aware (one‐back reaching, visuomotor transformation, and precued reaction time with variable predictive value of the precue). Patients specifically failed in those tasks where preplanning of movement could occur and under conditions of increasing certainty regarding the movement to be performed. However, they implicitly learned to adapt to a visuomotor transformation as well as healthy controls. We propose that when the movement to be performed can be preplanned or is highly predicted, patients with functional motor symptoms shift to an explicit attentive mode of processing that impairs kinematics of movement control, but movement becomes normal when such processes cannot be employed (e.g., during unexpected movement or implicit motor adaptation).

Psychogenic palatal tremor may be underrecognized: Reappraisal of a large series of cases

Palatal tremor is characterized by rhythmic movements of the soft palate and can be essential or symptomatic. Some patients can have palatal movements as a special skill or due to palatal tics. Psychogenic palatal tremor is recognized but rarely reported in the literature.

‘Jumping to conclusions’ bias in functional movement disorders

Background Patients with functional neurological disorders often report adverse physical events close to the onset of functional symptoms. However, the mechanism via which a triggering event may set off a functional condition is lacking. One possibility is that patients make abnormal inferences about novel information provided by physical triggering events. In this study, the authors aimed to specifically investigate whether patients with functional movement disorders have abnormalities in probabilistic reasoning. Methods The authors used a well-studied probabilistic reasoning paradigm, ‘the bead task’, in 18 patients with functional movement disorders and 18 healthy agematched controls. The authors assessed the number of beads that participants needed to reach a decision and changes in the certainty of their decisions when confronted with confirmatory or contradictory evidence. Findings Patients with functional movement disorders requested on average significantly fewer beads before reaching a decision than controls (3 vs 6 beads). When confronted with potentially disconfirmatory evidence, patients showed a significantly greater reduction in confidence in their estimates than controls. 40% of patients reached a decision after one or two beads whereas no controls showed this bias. Interpretation Patients with functional movement disorders requested less information to form a decision and were more likely to change their probability estimates in the direction suggested by the new evidence. These findings may have relevance to the manner with which patients with functional neurological disorders process novel sensory data occurring during physical triggering events commonly reported at onset of symptoms.

Functional (psychogenic) symptoms in Parkinson's disease

It has been reported that patients who have Parkinsons disease have a high prevalence of somatisation (functional neurological symptoms) compared with patients who have other neurodegenerative conditions. Numerous explanations have been advanced for this phenomenon. Here, with illustrative cases, we discuss this topic, including its clinical importance, and suggest a link between the pathophysiology of Parkinsons disease and the proposed propensity to develop functional symptoms.

Cerebellar transcranial direct current stimulation does not alter motor surround inhibition.

Motor surround inhibition (mSI) is one mechanism by which the central nervous system individuates finger movements, and yet the neuroanatomical substrate of this phenomenon is currently unknown. In this study, we examined the role of the cerebellum in the generation of mSI, using transcranial direct current stimulation of the cerebellum (cDC). We also examined intrasubject and intersubject variability of mSI. Twelve subjects completed a three session cross over study in which mSI was measured before and after (0 and 20 minutes) sham, anodal and cathodal cDC. mSI of the surround muscle (adductor digiti minimi) at the onset of flexion of the index finger was consistently observed. Anodal and cathodal cDC did not modulate the magnitude of mSI. For individual subjects (across the three sessions), the intrasubject coefficient of variation was 27%. Between subjects, the intersubject coefficient of variation was 47%. mSI was a stable effect in individual subjects across multiple sessions. This is an important observation and contrasts with other neurophysiological paradigms such as paired associative stimulation response, which exhibit great variability. In addition, we have quantified intrasubject variability of mSI, which will allow future therapeutic studies that attempt to modulate mSI to be adequately powered. We have not found evidence that the cerebellum contributes to the neuroanatomical network needed for the generation of mSI. Understanding the mechanisms of mSI remains a challenge but is important for disorders in which it is deficient such as Parkinsons disease and focal hand dystonia.

Cerebellar brain inhibition is decreased in active and surround muscles at the onset of voluntary movement

Highly selective activation of the desired muscles for each movement and inhibition of adjacent muscles is attributed to surround inhibition (SI) which differentially modulates corticospinal excitability in active and surrounding muscles. Cerebellar brain inhibition (CBI) is another inhibitory neuronal network which is known to be active at rest and during tonic muscle contraction. The way in which CBI may be modulated at movement onset and its relationship with SI has not previously been investigated. We assessed motor evoked potential (MEP) size and CBI in first dorsal interosseus (FDI) and abductor digiti minimi (ADM) muscles at rest and during a simple motor task where FDI was an active muscle and ADM was not involved in the movement (surround muscle). At onset of movement, MEP size in ADM was significantly suppressed, confirming the existence of SI. In contrast, CBI in both muscles was found to be significantly decreased at the onset of the movement. This was confirmed even after adjustments for changes in MEP size occurring due to onset of muscle activity in FDI and the effects of SI in ADM. Our findings fail to functionally link SI with CBI, but they do indicate a non-topographically specific modulation of CBI in association with initiation of voluntary movement.