Oculopalatal tremor (OPT) is an acquired syndrome characterized by continuous rhythmic movements of the soft palate and pendular nystagmus. It is also called oculopalatal myoclonus. When only palatal movements occur without ocular symptoms, it is referred to as palatal myoclonus.
The lesion site is a brainstem lesion affecting the Guillain-Mollaret triangle (dentato-rubro-olivary pathway), and the most common trigger is a cerebrovascular accident in the posterior circulation. It is a rare disease even among brainstem infarction patients; in a retrospective review of 82 cases by Jang et al., the mean age at diagnosis was 54 years, with a male predominance.
As for the underlying diseases, brainstem vascular lesions account for about 80%, and other causes include demyelinating diseases, infections, CNS inflammation, iatrogenic injury, and tumors.
Tonnu et al. (2022) reported a 58-year-old female case of palatal myoclonus and OPT due to hypertrophic olivary degeneration (HOD) caused by a Streptococcus intermedius brain abscess 2). Even after the brain abscess resolved, PT/OPT persisted, and this was the first reported case of S. intermedius as an infectious cause of HOD.
QHow rare is oculopalatal tremor?
A
It is a rare disease even among brainstem infarction patients. The largest report to date is a retrospective review of 82 cases by Jang et al., and the number of cases is too small to conduct large-scale clinical trials.
Palatal tremor: Rhythmic movement of the soft palate due to regular contraction of the levator veli palatini muscle. Usually persists during sleep.
Nystagmus: Synchronous or asynchronous pendular nystagmus. It may be convergent, vertical, or a combination. Oscillations are typically 1–3 Hz.
Waveform: Smooth sinusoidal oscillations. Elliptical waveforms are seen in OPT and seesaw nystagmus, suggesting lesions in the interstitial nucleus of Cajal or the midbrain tegmentum 1).
Changes during sleep: Nystagmus may disappear during sleep, but palatal movements persist.
Skew deviation: Vertical deviation may occur because the VOR pathway is near the Guillain-Mollaret triangle.
Affected sites: The palate is most commonly affected. Other sites include the eyes, facial muscles, pharynx, tongue, larynx, diaphragm, eustachian tube opening, and rarely the neck, trunk, and limbs.
There are two clinical types of OPT: lateral and midline.
Initially, the lateral type was associated with unilateral IONH and the central type with bilateral IONH. However, later studies did not show a sufficient correlation.
QDo palatal movements and nystagmus always occur simultaneously?
A
Palatal tremor and nystagmus can be either synchronous or asynchronous. When only rhythmic palatal movements occur without nystagmus, it is called “palatal myoclonus” and is distinguished from OPT.
Brainstem vascular lesions: The most common cause, accounting for about 80% of cases. Infarction or hemorrhage in the posterior circulation disrupts the dentatorubrothalamic tract.
Infections: Brain abscess (e.g., S. intermedius, Toxoplasma, Listeria) 2).
CNS inflammation: Autoimmune diseases.
Iatrogenic injury: Surgery on the brainstem or cerebellum.
Trauma: Traumatic injury to the brainstem or cerebellum.
Tumor: Brainstem tumor.
Vascular malformation: Among causes of HOD, cavernous hemangioma is considered the most common 2).
Onset timing ranges from 3 weeks to 49 months after the initial injury, but typically occurs within 6 to 8 months (median 10 months) 2). Familial diseases causing inferior olivary nucleus degeneration (such as Alexander disease, POLG mutations, SCA20, etc.) can also be causes.
MRI findings are important as an aid to diagnosis.
T2 hyperintensity: Unilateral or bilateral hyperintensity appears in the inferior olivary nucleus of the upper medulla oblongata. Also referred to as the “pimento sign.”
Timing of appearance: It begins to be observed several months after the initial injury.
Natural course: T2-FLAIR hyperintensity at 1 month → hypertrophy of the olive at 6 months → resolution in 3–4 years2).
DTI: Diffusion tensor imaging can visualize fiber tract disruption and is useful for understanding the anatomy of HOD2).
Normal MRI: Rarely, MRI may be normal.
Histologically, hypertrophic vacuolated neurons and hypertrophic astrocytes are observed.
OPT is included in the broad category of myoclonus (repetitive rhythmic movements at 1–4 Hz at rest). Differentiation from the following conditions is important.
Acquired pendular nystagmus due to multiple sclerosis: Slightly faster at 3–5 Hz, without orofacial movements. Caused by lesions in the paramedian pathways 1). It differs from OPT in that the abnormal rhythm originates from IONH as a pacemaker and is accompanied by palatal movements.
Oculomasticatory myorhythmia: Convergence-divergence or vertical nystagmus accompanied by rhythmic contractions of facial and masticatory muscles. Often seen secondary to Whipple disease 1).
Epilepsia partialis continua: Focal slow rhythmic tremor. Can be differentiated by EMG (short burst duration) and EEG (jerky synchronous potentials).
Holmes tremor: Resting, postural, and kinetic tremor belonging to the same category of myorhythmia.
Hypomagnesemia: Can present with acute reversible cerebellar ataxia and pendular nystagmus. A reversible metabolic cause that improves within hours with Mg supplementation should be ruled out 3).
Gabapentin: Moderate efficacy has been reported for acquired pendular nystagmus1).
Memantine: A mechanism involving reduction of synchronized firing at the inferior olive level via NMDA receptor blockade has been proposed1).
Baclofen: Listed as one of the therapeutic agents for acquired pendular nystagmus1).
Anticholinergics (trihexyphenidyl, scopolamine): Moderate efficacy, but therapeutic effect is limited by anticholinergic side effects such as confusion and drowsiness.
Medications for palatal myoclonus: Carbamazepine, lamotrigine, and sodium valproate have been reported2).
There is no solid evidence that these drugs are effective for palatal tremor.
Retrobulbar botulinum toxin injection: May provide temporary relief in certain situations. However, it carries risks of retrobulbar hemorrhage, extraocular muscle palsy, and ptosis.
Botulinum toxin injection into the palate: Reported as a symptomatic treatment for palatal myoclonus2).
OPT usually follows a refractory course. PT/OPT progressively worsens over 5–24 months after onset, and improvement or complete resolution is rare2). Persistent oscillopsia can cause severe impairment in daily life.
QCan oculopalatal tremor be completely cured with treatment?
A
Currently, there is no curative treatment. Both pharmacotherapy and surgical interventions are highly resistant to treatment, and spontaneous remission is rare. This is a refractory disease that can cause severe functional impairment due to persistent oscillopsia.
The core of the pathophysiology of oculopalatal tremor lies in the disruption of the Guillain-Mollaret triangle. This circuit consists of the following pathways:
Cerebellar dentate nucleus → superior cerebellar peduncle (decussation) → contralateral red nucleus → central tegmental tract (ipsilateral descending) → ipsilateral inferior olive
The laterality of IONH is determined by the site of damage within this triangle.
Dentate nucleus lesion
Lesion site: Cerebellar dentate nucleus
IONH appearance: Hypertrophic degeneration occurs in the contralateral inferior olive.
Mechanism: The ascending pathway from the dentate nucleus to the red nucleus is disrupted, leading to loss of inhibitory input to the contralateral olive.
Central Tegmental Tract Injury
Injury site: Central tegmental tract
IONH appearance: Hypertrophic degeneration occurs in the ipsilateral inferior olive.
Mechanism: The descending pathway from the red nucleus to the olive is disrupted, blocking input to the ipsilateral olive.
Mechanism of Inferior Olivary Nucleus Hypertrophy (IONH)
Within the damaged inferior olive, abnormal soma-somatic gap junctions and electrical coupling form between neurons. This generates irregular and abrupt signals, which are ultimately modified via climbing fibers to the cerebellum and manifest as smooth, rhythmic pendular nystagmus.
NMDA receptors are involved in synchronized firing at the inferior olive level, and memantine blockade of NMDA receptors is thought to reduce this firing. It is also believed that denervation hypersensitivity causes the inferior olive to generate rhythmic impulses that are transmitted to the extraocular and palatal muscles1).
QWhy does the olive nucleus hypertrophy despite nerve damage?
A
Normal axonal injury leads to atrophy, but IONH is a pseudohypertrophy. Denervation of the dentato-olivary pathway releases tonic inhibition on olivary neurons, resulting in persistent synchronized oscillations. This abnormal neural activity is thought to cause hypertrophy of neurons and astrocytes2).
7. Latest Research and Future Perspectives (Research-stage Reports)
Tonnu et al. (2022) successfully used diffusion tensor imaging (DTI) to visualize the disruption of the central tegmental tract and superior cerebellar peduncle in 3D in a case of HOD 2). Precise delineation of the lesion site within the GMT using DTI is rare, and it is expected to serve as an anatomical basis for future neuromodulation therapy.
Polanco et al. (2024) reported a case of a 64-year-old man with severe hypomagnesemia (Mg <0.5 mg/dL) who presented with horizontal pendular nystagmus and cerebellar ataxia 3). Intravenous Mg (22.5 g on the first day, followed by an additional 13.5 g over 15 days) led to resolution of nystagmus within hours. This report highlights the importance of ruling out reversible metabolic causes in the differential diagnosis of OPT.
Due to the rarity of OPT, large-scale clinical trials have not been conducted at this time, and the level of evidence for treatment is low. The development of new therapies, including neuromodulation, is a future challenge.
Gurnani B, et al. Nystagmus: A Comprehensive Review of Pathophysiology, Classification, Diagnosis, and Management. Clin Ophthalmol. 2025;19:1617-1645.
Tonnu A, Hunt R, Zervos T, et al. Hypertrophic olivary degeneration and palatal myoclonus from a Streptococcus intermedius infection of the brain: illustrative case. J Neurosurg Case Lessons. 2022;3(24):CASE2265.
Polanco M, Rivera M, Manrique L, et al. Horizontal Pendular Nystagmus and Ataxia Secondary to Severe Hypomagnesemia. Tremor Other Hyperkinet Mov. 2024;14(1):38.
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