Symptomatic Palatal Tremor Research Articles

The ‘essentials’ of essential palatal tremor: a reappraisal of the nosology

Essential palatal tremor (EPT) is an uncommon disorder, distinct from symptomatic palatal tremor (SPT), but characterized by superficially similar rhythmic movements of the soft palate. While the pathophysiology of SPT has been relatively well defined, this is not the case in EPT. Based on an analysis of 103 published cases, we reviewed EPT in the context of other movement disorders with similar features and outline possible pathophysiological mechanisms. Phenomenologically it remains best classified as a tremor. Four major causes, including a central generator, peripheral/mechanical, voluntary/special skill and psychogenic, appear to account for the majority of cases of EPT, although there is considerable overlap in the pathogenic mechanisms underlying these categories. Among the cases reviewed, a large proportion fit into the latter two categories, although there are others where multiple mechanisms are likely at play. Based on our reappraisal, we suggest a change in designation to 'isolated palatal tremor', with primary and secondary subtypes. This retains the distinction from SPT and emphasizes the non-uniform, heterogeneous nature of the disorder.

Generation of symptomatic palatal tremor is not correlated with inferior olivary hypertrophy.

Although the generation of symptomatic palatal tremor (SPT) is thought to derive from the abnormal activity of hypertrophic inferior olivary neurones, the actual mechanism of SPT has not yet been elucidated. We therefore investigated the relationship between SPT and the pathological process of inferior olivary hypertrophy (IOH). We examined 16 autopsied subjects with cerebrovascular lesions of the dentate-olivary tracts. We analysed the size of the olives, the number of olivary neurones, synaptic, axonal and astrocytic changes in the olives and the clinical course in the subjects. SPT was observed in eight patients, in seven of whom it appeared 1-2 months after interruption of the afferents then progressed to reach a peak approximately 1-2 years from the onset. SPT persisted for the rest of the subjects' lives without decreasing in severity. Neuronal hypertrophic change began 20-30 days after the onset of the causative lesions and reached maximum size, accompanied by prominent astrocytosis and synaptic and axonal remodelling, 6-7 months later. The number of olivary neurones decreased to <10% of that in controls in patients who survived >6 years. Despite the persistence of SPT, both the myelin and the axons of efferent fibres from olivary neurones were severely degenerated in patients who survived several years. Therefore, the appearance of SPT may depend on the hyperactivity of olivary neurones released from inhibitory inputs until the peak of both IOH and SPT. However, the persistence of peak intensity and distribution of established SPT is probably due to both the disturbance of natural rhythmicity in the body and the lack of feedback from the abnormal movement resulting from the dysfunction of the olive.

The pathophysiology of tremor.

Tremor is defined as rhythmic oscillatory activity of body parts. Four physiological basic mechanisms for such oscillatory activity have been described: mechanical oscillations; oscillations based on reflexes; oscillations due to central neuronal pacemakers; and oscillations because of disturbed feedforward or feedback loops. New methodological approaches with animal models, positron emission tomography, and mathematical analysis of electromyographic and electroencephalographic signals have provided new insights into the mechanisms underlying specific forms of tremor. Physiological tremor is due to mechanical and central components. Psychogenic tremor is considered to depend on a clonus mechanism and is thus believed to be mediated by reflex mechanisms. Symptomatic palatal tremor is most likely due to rhythmic activity of the inferior olive, and there is much evidence that essential tremor is also generated within the olivocerebellar circuits. Orthostatic tremor is likely to originate in hitherto unidentified brainstem nuclei. Rest tremor of Parkinson's disease is probably generated in the basal ganglia loop, and dystonic tremor may also originate within the basal ganglia. Cerebellar tremor is at least in part caused by a disturbance of the cerebellar feedforward control of voluntary movements, and Holmes' tremor is due to the combination of the mechanisms producing parkinsonian and cerebellar tremor. Neuropathic tremor is believed to be caused by abnormally functioning reflex pathways and a wide variety of causes underlies toxic and drug-induced tremors. The understanding of the pathophysiology of tremor has made significant progress but many hypotheses are not yet based on sufficient data. Modern neurology needs to develop and test such hypotheses, because this is the only way to develop rational medical and surgical therapies.

Modulation of symptomatic palatal tremor by magnetic stimulation of the motor cortex

Objectives: Magnetic stimulation of the motor cortex can be used to determine the involvement of the cortex in rhythmic movement disorders. Symptomatic palatal tremor (SPT) is thought to come from a pacemaker that is relatively resistant to internal and external stimulation. In this study, we investigated the effect of magnetic stimulation of motor cortex on SPT. Methods: Five male patients, aged 67–79 years, with SPT after brain stem infarction or hemorrhage, all had a synchronous mouth angle twitch with the palatal movement. Electromyographic activity was recorded with a monopolar needle electrode from orbicularis oris. In experiment 1, transcranial magnetic stimulation (TMS) was delivered at 200% motor threshold (MT) to reset SPT. In experiment 2, the effect of TMS intensities was studied at 80–240% MT in two SPT patients. To determine the influence of the TMS, we used the resetting index (RI). Results: TMS reset the tremor in all 5 SPT patients at 200% MT with RIs of 0.86–0.96. The latency of the tremor reappearance after TMS was longer than the pre-stimulus tremor interval, and the intervals between the subsequent tremor bursts were also prolonged. The degree of tremor resetting was closely correlated with the magnetic stimulus intensity and the latency of the tremor reappearance after TMS. Conclusions: Stimulation of the motor cortex may modulate the generator of SPT.

Action palatal tremor in a patient with primary intestinal lymphoma

We report the case of a 59-year-old man with primary intestinal T-cell non-Hodgkin's lymphoma who developed abnormal facial twitching synchronous with small palatal movements induced by attempts at speaking or swallowing. At rest, the electromyogram (EMG) showed no spontaneous muscular activity. Phonation triggered trains of synchronous, rhythmic EMG bursts at a frequency of 3-4 Hz lasting 10-20 s, with an average burst of 150 ms, which simultaneously involved palatal, facial, and neck muscles bilaterally with left-sided predominance. An enhanced blink reflex recovery curve was observed after stimulation of either side. Backaveraging electroencephalographic study revealed no activity that was time locked with the jerks. Axial T2-weighted magnetic resonance imaging showed an increased signal intensity and bilateral enlargement of the inferior olives. No antineuronal-specific antibodies were found in the blood or in the cerebrospinal fluid. All of these clinical findings were consistent with a symptomatic palatal tremor (PT). Because it was triggered by activation of cranial muscles, we termed this movement disorder action PT. To our knowledge, this is the first report of symptomatic PT displaying these features.

Symptomatic and essential palatal tremor. 3. Abnormal motor learning.

Palatal tremor is divided into symptomatic palatal tremor (SPT) and essential palatal tremor (EPT) on the basis of clinical features. The inferior olive seems to be abnormal in SPT, but not EPT. Because the inferior olive is likely to be involved in several types of motor learning, it is hypothesised that motor learning would be abnormal in patients with SPT, but not those with EPT. In six patients with SPT and four patients with EPT, two motor learning paradigms were studied--the classical conditioning of an acoustically elicited eyeblink with electrical supraorbital nerve shock and a test of adaptation of ballistic arm movements to a change of the gain. Classical conditioning was impaired unilaterally or bilaterally in the patients with SPT, depending on whether they had unilateral or bilateral abnormalities of the inferior olives, except for the two least affected patients. All but one of the patients with EPT had normal conditioning. On the adaptation test of arm movements, most of the patients with SPT had impaired learning of the arm contralateral to the hypertrophied inferior olive, regardless of whether the abnormality was unilateral or bilateral, but all patients with EPT had normal results. In SPT pseudohypertrophy of the inferior olive leads to defective cerebellar function, whereas in EPT the inferior olive functions normally.

Symptomatic and essential palatal tremor. 1. Clinical, physiological and MRI analysis.

Palatal tremor (brief, rhythmic involuntary movements of the soft palate) apparently comprises two different nosological entities: essential palatal tremor (EPT) and symptomatic palatal tremor (SPT). The site of the abnormality in EPT is unknown, whereas SPT is believed to arise from a lesion of the brainstem or cerebellum (within the Guillain-Mollaret triangle). The clinical and physiological properties of these conditions were studied in four patients with EPT and six patients with SPT. Patients with EPT had normal cerebellar function, but those with SPT had clinical signs of cerebellar dysfunction. The palatal movements were consistent with activation of the tensor veli palatini muscle in EPT and of the levator veli palatini muscle in SPT. During sleep, EPT stopped, whereas SPT continued with only slight variations in the tremor rate. The cycle of palatal tremor could not be reset by stimulation of trigeminal afferents in either EPT or SPT patients, and Valsalva's manoeuvre did not consistently affect the rhythm of the tremor in either group. The palatal tremor cycle exerted remote effects on the tonic electromyographic activity of the upper and lower extremities only in patients with SPT. These effects were present only on the side of the cerebellar signs (opposite the side with the enlarged inferior olive) in patients with a unilateral syndrome. Essential palatal tremor patients had only polysynaptic brainstem reflex abnormalities, whereas SPT patients had abnormalities of monosynaptic, oligosynaptic and polysynaptic brainstem reflexes. Magnetic resonance imaging showed no evidence of structural abnormalities in EPT patients, but SPT patients had a hyperdense signal of the ventral upper medulla (the region of the inferior olive) on T2-weighted images. These observations support the hypothesis that EPT and SPT are two different diseases. In SPT, cerebellar dysfunction ipsilateral to the palatal tremor may be due, in part, to abnormal function of the contralateral hypertrophic inferior olive. The proposed basis of SPT is a disturbance of electrotonic coupling between the cells of the inferior olive induced by a lesion of the dentato-olivary pathway. Similar mechanisms could be responsible for postural tremors in general. The pathophysiological basis of EPT remains unknown.

Symptomatic and essential palatal tremor. 2. Differences of palatal movements.

Palatal tremor, a rhythmic movement disorder of the soft palate, may be described as two separate entities: symptomatic palatal tremor (SPT) and essential palatal tremor (EPT). The symptomatic form is associated with brain stem or cerebellar disease, whereas the essential form has no known etiology. A cardinal symptom of EPT is the presence of ear clicks, which do not occur in SPT. Visual observation of the movements in the two disorders suggests that the difference in symptoms is due to the activation of different palatal muscles, the levator veli palatini in SPT and the tensor veli palatini in EPT. Electromyographic recording from the levator veli palatini muscle showed abnormal bursting activity time locked to the palatal movements in patients with SPT, but not in those with EPT. Because the two palatal muscles are innervated by different cranial nerves, SPT and EPT are likely to have separate origins.

Termination of spinal afferents to inferior olive in cat.

Termination of spinal afferents to inferior olive in cat.