Introduction

Palatal myoclonus, also referred to as palatal tremor, is a rare movement disorder characterised by rhythmic, involuntary contractions of the soft palate. When the condition is accompanied by synchronous ocular movements, it is termed oculopalatal myoclonus (OPM). The disorder is conventionally divided into two major categories: essential palatal myoclonus (EPM) and symptomatic palatal myoclonus (SPM). The distinction is clinically important because the two forms differ in aetiology, associated symptoms, and response to treatment.

This article reviews illustrative cases of palatal myoclonus, highlighting the typical presentations, underlying pathophysiological mechanisms, and management strategies that clinicians encounter in practice.

Case 1: Essential Palatal Myoclonus Presenting with Ear Click

Presentation

A 34-year-old individual presented with a persistent clicking sound in the left ear that had been present for two years. The clicking was audible to the examiner and occurred at a rate of approximately 120 beats per minute. The patient reported that the noise was distracting, interfered with sleep, and caused significant anxiety. There was no history of neurological disease, stroke, or head trauma. Neurological examination was otherwise entirely normal, with no cerebellar signs, no nystagmus, and no limb myoclonus.

Clinical Findings

Close inspection of the oral cavity revealed rhythmic contractions of the tensor veli palatini muscle, which opened the Eustachian tube with each contraction. This accounted for the audible click. Magnetic resonance imaging (MRI) of the brain, including thin-section imaging through the brainstem, was unremarkable. There was no evidence of hypertrophic olivary degeneration or structural lesions in the Guillain-Mollaret triangle.

Diagnosis and Management

The diagnosis of essential palatal myoclonus was made on the basis of the isolated ear click, normal neurological examination, and absent radiological abnormalities. The patient was initially managed with reassurance and explanation of the benign nature of the condition. However, because the symptom remained intrusive, a trial of a gamma-aminobutyric acidergic agent was initiated. The clicking reduced in intensity, and the patient reported improved quality of life. Injections of botulinum toxin into the tensor veli palatini were discussed as a second-line option if oral therapy proved insufficient.

Case 2: Symptomatic Palatal Myoclonus Following Brainstem Infarction

Presentation

A 58-year-old individual with a history of hypertension and diabetes developed sudden vertigo, dysarthria, and gait ataxia. Imaging confirmed an acute infarction involving the right cerebellar hemisphere and the dorsolateral brainstem. In the weeks following the stroke, the patient developed a progressive rhythmic movement of the soft palate, associated with oscillopsia, or the subjective sensation that the visual world was bouncing. Examination demonstrated synchronous contractions of the palate and both eyes, consistent with oculopalatal myoclonus.

Clinical Findings

The palatal movements in this case involved the levator veli palatini, a muscle supplied by the vagus nerve via the nucleus ambiguus. The eye movements were vertical oscillations with a frequency matching the palatal contractions. Serial MRI performed three months after the stroke revealed signal change and enlargement of the inferior olivary nucleus in the medulla, a finding known as hypertrophic olivary degeneration. This radiological abnormality is the hallmark of symptomatic palatal myoclonus and reflects trans-synaptic degeneration within the Guillain-Mollaret triangle.

Diagnosis and Management

The diagnosis of symptomatic palatal myoclonus was confirmed by the combination of the characteristic clinical picture, the preceding brainstem stroke, and the evolution of hypertrophic olivary degeneration on imaging. Treatment focused on the underlying vascular risk factors to prevent further strokes. The palatal tremor itself was managed symptomatically. Pharmacological therapy with a gamma-aminobutyric acidergic agent produced only modest benefit. Trials of other agents, including anticholinergics and serotoninergic drugs, were also only partially effective. The oscillopsia was particularly disabling, and the patient was referred for consideration of botulinum toxin injections into the palatal muscles. This intervention provided partial relief of the oscillopsia, although careful dosing was required to avoid dysphagia.

Case 3: Oculopalatal Myoclonus Associated with Hypertrophic Olivary Degeneration

Presentation

A 45-year-old individual presented with a six-month history of progressive clumsiness, slurred speech, and involuntary eye movements. The patient had been treated for a cavernous malformation in the brainstem several years earlier. Over time, the patient developed rhythmic palatal movements and disabling vertical oscillations of both eyes. The eye movements worsened with attempted fixation, and the patient found reading and walking particularly difficult because of the constant motion of the visual scene.

Clinical Findings

Neurological examination showed palatal tremor, ocular myoclonus, and signs of cerebellar dysfunction, including dysmetria and ataxic gait. Brain MRI demonstrated a characteristic lesion in the region of the Guillain-Mollaret triangle, with marked hypertrophic degeneration of the inferior olivary nucleus. The imaging features were consistent with a remote insult to the dentato-olivary pathway, in this case related to the prior cavernous malformation and its treatment.

Diagnosis and Management

The diagnosis of oculopalatal myoclonus secondary to hypertrophic olivary degeneration was established. The patient was treated with a combination of medications, including a gamma-aminobutyric acidergic agent and a serotonin precursor. Partial improvement in the amplitude of the ocular oscillations was observed, but the palatal tremor persisted. The patient experienced significant disability from the oscillopsia and was offered botulinum toxin injection into the submental or palatal muscles. The procedure resulted in reduced palatal contractions, but the ocular oscillations remained largely unchanged. Long-term follow-up focused on symptomatic support, fall prevention, and adaptation strategies for the visual disturbance.

Pathophysiology and the Guillain-Mollaret Triangle

The final common pathway for symptomatic palatal myoclonus involves a circuit known as the Guillain-Mollaret triangle. This triangle connects the dentate nucleus of the cerebellum, the red nucleus of the midbrain, and the inferior olivary nucleus of the medulla. Damage to this circuit, whether from stroke, trauma, infection, demyelination, or neoplasm, can lead to a characteristic pattern of trans-synaptic degeneration in the inferior olive. The degenerated olive becomes enlarged and shows signal change on MRI, a finding referred to as hypertrophic olivary degeneration.

Symptomatic palatal myoclonus typically begins weeks to months after the initial insult and is often permanent. The palatal movements in this form are caused by contraction of the levator veli palatini, which is innervated by the vagus nerve. In contrast, essential palatal myoclonus involves the tensor veli palatini, which is innervated by the trigeminal nerve. This distinction in muscle involvement explains why essential palatal myoclonus is more likely to produce an audible ear click, as the tensor veli palatini opens the Eustachian tube.

Clinical Features and Diagnostic Workup

The diagnosis of palatal myoclonus is primarily clinical. Observation of the rhythmic palatal movements and, when present, synchronous ocular oscillations is sufficient to establish the diagnosis. However, a careful history and examination are required to distinguish the essential from the symptomatic form.

• Essential palatal myoclonus: Isolated ear click, normal neurological examination, no brainstem pathology on imaging, and no associated ocular myoclonus.
• Symptomatic palatal myoclonus: Palatal tremor due to levator veli palatini contraction, frequently accompanied by ocular myoclonus, cerebellar signs, or other brainstem features, with an identifiable lesion in the Guillain-Mollaret triangle.

Magnetic resonance imaging is the most valuable investigation. The demonstration of hypertrophic olivary degeneration on MRI strongly supports the symptomatic form. In essential palatal myoclonus, imaging is typically normal. Additional investigations, such as electrophysiological studies, may be used to characterise the myoclonus but are not essential for diagnosis.

Treatment Considerations

Treatment of palatal myoclonus is symptomatic. Essential palatal myoclonus with a bothersome ear click may be treated with oral medications, including gamma-aminobutyric acidergic agents, anticholinergics, or sodium channel blockers. When oral therapy fails, botulinum toxin injection into the tensor veli palatini is highly effective and is often considered the treatment of choice for the ear click.

Symptomatic palatal myoclonus is generally more refractory to treatment. The underlying cause should be managed appropriately, such as vascular risk factor control in patients with stroke. Oral medications may reduce the amplitude of the movements, but complete suppression is uncommon. Botulinum toxin injections into the levator veli palatini can reduce palatal tremor, but careful monitoring is required to avoid dysphagia and nasal regurgitation. Ocular oscillations associated with oculopalatal myoclonus are particularly difficult to treat and may require a multidisciplinary approach involving a neurologist and an ophthalmologist.

Summary

Palatal myoclonus is an uncommon but distinctive movement disorder with two clinically and pathophysiologically distinct forms. Essential palatal myoclonus presents with an isolated ear click, a normal neurological examination, and normal imaging, while symptomatic palatal myoclonus arises from structural damage to the Guillain-Mollaret triangle and is frequently associated with hypertrophic olivary degeneration and oculopalatal myoclonus. Accurate diagnosis depends on careful clinical observation and targeted imaging. Management is symptomatic, with botulinum toxin offering a valuable option for the disabling symptoms of both forms, particularly the audible ear click of essential palatal myoclonus and the troublesome oscillopsia of the symptomatic form.