Palatal tremor secondary to a dolichoectatic basilar artery
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/neuroindia.NI_983_16
Source of Support: None, Conflict of Interest: None
Among the rhythmic hyperkinesias, palatal tremor (PT) is one of the rare movement disorders, which was first described by Politzer in 1878. In the literature, PT has been described by various eponyms such as ‘cephalic murmur', ‘chorea of the soft palate', and ‘rhythmic myoclonus'. Even today, many authors use the term ‘palatal myoclonus'.
The unique phenomenology of the PT overlaps with, but does not strictly adhere to, the classic concept of either tremor or myoclonus. Authors opposed to the definition of palatal tremor draw attention to the fact that tremors associated with a specific condition tend to have a relatively constant and characteristic frequency; however, the frequency of palatal tremor reported in different individuals is not only highly variable, it also tends to vary in the same individual., Proponents of the term ‘palatal myoclonus’ cite cases where the movements respond to the drugs influencing either the gamma-aminobutyric acid [GABA] pathway (for example, valproate), or the serotonin pathway (for example, sumatriptan). Both these neurotransmitter pathways are implicated in the causation of various forms of myoclonus. Furthermore, unlike other tremors, PT is also known to be present in sleep in 50% of the cases. Many patients with early stages of the tremor can exert some control over their tremor and suppress it by performing various ‘tricks', which are not a usual feature in tremor disorders, and are more reminiscent of dystonia.,,, Indeed, a patient was described who had dystonic signs in addition to the presence of PT; however, the author described this association as being an exception rather than a rule. Although the classification system of PTs remains imperfect, considering that the disorder meets all the criteria of a tremor (i.e., a rhythmic, ongoing movement of at least one functional region, in this case, the soft palate), theFirst International Congress of Movement Disorders in 1990 reclassified it as a tremor.
Schenk recognized two types of PTs that were subsequently named the "essential palatal tremor"(EPT) and the "symptomatic palatal tremor"(SPT) [Table 1]. Based on their review of palatal tremor patients, Deuschl et al., (reporting on 287 cases; 77 with EPT and 210 with SPT) and Zadikoff et al., (reporting on 103 cases with EPT) observed that the patients with EPT usually have objective ear clicks as their typical complaint, which tends to be rare in the symptomatic form. The eye and extremity muscles are never involved in EPT. SPT patients tend to be unaware of their palatal movements but often present with signs and symptoms suggestive of brainstem or cerebellar dysfunction. The jerk frequency is lower in essential than in symptomatic palatal tremor, and patients with EPT are younger and have a balanced gender distribution compared with a male preponderance in the symptomatic form.,
We are reporting the case of a patient who had PTs secondary to a dolichoectatic basilar artery. To the best of our knowledge, this type of presentation has not been previously described.
A 65-year-old male patient, who was hypertensive and a smoker presented with a one-year history of progressive gait imbalance, easy forgetfulness, and slowness. Examination revealed a mini-mental scale score of 21/30 (despite the patient having the educational qualification of a postgraduate student). He also had bilateral pyramidal and extrapyramidal signs with subtle cerebellar signs on the right side. The oral examination revealed a constant rhythmic movement of the soft palate that was predominant on the posterior part on both the sides [Video 1]. He was not aware of the movements and also denied having ever heard a click. Based on the typical movements, a diagnosis of PTs was made and he was further investigated. A recent magnetic resonance imaging (MRI) [Figure 1]a-[Figure 1]d] of the brain showed multiple T2 white matter hyperintense lesions, especially in the area of the pons suggestive of chronic infarcts. In addition, the imaging revealed a hyperintense signal intensity in the region of the inferior olive, suggestive of olivary hypertrophy. Also noted was a very tortuous and dilated basilar artery that was deviated from its usual midline position. As discussed further, the most common vascular manifestation of the dolichoectasia of the basilar artery is a pontine infarct. Moreover, the underlying etiology in most SPT patients is brainstem infarct. We, therefore, ascribed the patient's SPT to the development of a pontine infarct secondary to dolichoectasia. Thus, the case represents one of the rare movement disorders (SPT) that was caused by an equally rare vascular anomaly (dolicobasilar ectasia).
The term ‘dolichoectasia’ is derived from the combinations of the Greek words ‘dolichos,’ meaning ‘abnormally long,’ and ‘ectasis,’ meaning ‘to extend or dilate.’ It, thus, refers to an elongated, tortuous, and sometimes aneurysmal, blood vessel. The Italian anatomist, Giovanni Morgagni, first described these elongated and dilated arteries in 1761. Although anterior circulation may be affected, the posterior circulation arteries are particularly susceptible to dolichoectasia, and consequently the brainstem structures, especially the cranial nerves, seem to be the structures most susceptible to the compression effects of the ectasia., Dolichoectasia tends to be associated with hypertension, old age, and other cardiovascular risk factors.,, Patients may present with cerebral infarction, intracerebral hemorrhage, or transient ischemic attacks as a part of the vascular sequel of ectasia.
Smoker et al., established the criteria for assessing dolichoectasia in basilar arteries that were based on computed tomographic angiography (CTA) findings. However, a noncontrast MRI has been shown to be as accurate as a CTA in correctly identifying the dolichoectasia. Its only drawback is that it slightly underestimates the basilar artery diameter.
Nishizaki et al., in their study that included 23 patients having a dolichoectatic basilar artery, reported pontine infarction to be the most common presentation, followed equally by symptoms suggestive of vertebrobasilar insufficiency and facial spasm. A dolichoectatic basilar artery was incidentally detected in 2 patients; however, not even a single patient having palatal tremors was detected in this large series. Thus, our case probably represents the first reported case of dolichoectatic basilar artery that resulted in the development of an SPT.
SPT, as described earlier, is associated with hypertrophy of the inferior olivary nucleus in the brainstem. This inferior olive is a part of the Guillain-Mollaret triangle (which is a component of the dentato-rubro-olivary network).
This triangle is composed of the contralateral dentate nucleus, ipsilateral red nucleus, and the ipsilateral inferior olivary nucleus. The study of this neuroanatomical pathway has evolved from the first descriptions of the inferior olivary enlargement, emphasized through the seminal work performed by Guillain and Mollaret, who described the functional triangle in 1931.
The triangle is completed by the decussating fibers originating from the inferior olivary nucleus, forming the largest component of the inferior cerebellar peduncle (corpus restiform), and terminating on the dentate nucleus.
The inferior olive has an intrinsic slow, rhythmic, and spontaneous activity. Despite being considered a complete functional triangle, SPT and hypertrophy of the inferior olive only occur with lesions involving the first two limbs of the triangle and not with interruption of the olivodentate fibers. This is because the olivary deafferentation is thought to trigger the hypertrophic degenerative changes. Oppenheim was the first to provide postmortem evidence for the presence of inferior olivary enlargement in cases of SPT; however, with the availability of MRI, an antemortem diagnosis can be made. Functional MRI in a 41-year old patient with stimulus-sensitive EPT demonstrated peak neuronal activation in the putamen bilaterally without any activation of the structures of the Guillain–Mollaret triangle. The authors ascribed this EPT to be due to the release of the basal ganglia (in this case, the putamen) from an inhibitory effect of the Guillain–Mollaret triangle. A recent case report described a 35-year old man with PT after a left middle cerebral artery ischemic stroke, without any evidence of brainstem infarction. The authors hypothesized that the onset of PT was either the result of epileptiform activity arising from the left frontal motor cortex or due to diaschisis (a sudden loss [or change] of function in a portion of the brain connected to a distant, but damaged, brain area), where the cortical infarction temporarily produced dysfunction of its subcortical connections within the dentato-rubro-olivary pathway.
SPT does not bother the patient and is, therefore, not specifically treated. Attention is, therefore, directed toward the underlying cause. Specific therapies for addressing basilar artery dolichoectasia do not currently exist. Thus, if a patient with this condition presents with stroke, the current evaluation and management options available to the treating physician are those routinely used for patients with ischemic or hemorrhagic stroke. When a dolichoectatic basilar artery is found by utilizing a CT or MR scan, it may be wise to treat these patients with platelet anti-aggregation therapy to prevent a brainstem or cerebral infarction, even in the absence of clinical evidence of ischemia. For asymptomatic patients, conservative management is preferred, although clip reconstruction has sometimes been attempted. Successful treatment of symptomatic patients has been reported with numerous other techniques including microvascular decompression with vessel repositioning, surgical reduction of the basilar artery diameter, and dolichoectasia vessel bypass and exclusion.,, In patients with dolichoectasia of the basilar artery, the benefits of surgery remain to be established, and cases of progression, despite surgery, have been reported.
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