REM behaviour disorder preceding palatal tremor

1. Introduction 

We present a case of idiopathic REM behaviour disorder (RBD) that preceded the development of palatal tremor and ataxia by 2 years. This association has not been previously described. The syndrome of palatal tremor with ataxia (PAPT) is considered by some authors as a distinct neurodegenerative disease. In our case the combination of RBD, cerebellar and extrapyramidal dysfunction guided our diagnostic thought towards multiple system atrophy (MSA). After a 6-year follow-up, however, there were no signs of autonomic dysfunction, making the diagnosis of MSA unlikely. The case is accompanied by two video sequences; the first displays the RBD and the second the palatal tremor.

2. Case description 

A 63-year-old man was referred for abnormal behaviour during sleep over the past 2 years. He was a non smoker with a body mass index of 23, drank alcohol occasionally, took no medication and had no other past medical history. His sleep history was free of excessive daytime sleepiness, restless legs or other sleep disorders. Physical examination was unremarkable with no signs of neurological dysfunction. The behaviour was compatible with RBD consisting of vocalization and violent limb movements always accompanied by a nightmare. He had thrown himself out of bed multiple times and once tried to strangle his wife. The patient underwent a full night video-polysomnography (VPSG) that revealed periodic leg movements (PLMs) with an index of 36 events/h, mild obstructive apnoea–hypopnoea (OSA) with an apnoea–hypopnoea index (AHI) of 8 events/h, and highly disrupted REM periods with REM sleep without atonia (Fig. 1) and violent behaviour recorded on video (Video 1). His haemoglobin and ferritin levels were normal and he was commenced on 0.75mg clonazepam each night which adequately controlled his behaviour.

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Fig. 1. Night polysomnography, 30s epoch. Montage: EOG (left-A2, right-A1), EEG (F3-A2, F4-A1, C3-A2, C4-A1, O1-A2, O2-A1), EMG (chin), LEGS (right+left leg in one bipolar channel), ECG, pulse, SpO2, nasal pressure, flow CU (nasal cannula), thorax abdomen (inductive plethysmography), snore CU, position. Movement artefacts and loss of muscle atonia during REM sleep.

Two years later the patient gradually developed diplopia and a mild gait disturbance. Neurological examination revealed nystagmus, diplopia, slurred speech and bilateral arm and leg dysmetria. He walked with a wide-based gait and could not heel-toe walk. There were no signs of pyramidal, sensory or autonomic disturbance. Investigations for cerebellar degeneration (vitamin-E, anti-Yo, anti-Hu, anti-Ri, chest and abdomen CT, cerebrospinal fluid, MRI of the brain) were negative. At the same time the patient complained of a re-emergence of his RBD. A further increase of clonazepam increased his unsteadiness. He commenced on ropinirole 4mg/day and his RBD improved almost instantaneously. On follow-up examination 3-months later a 1–2Hz palatal tremor was noticed (Video 2) without presence of ear clicks or other new symptoms. A new MRI of the brain was again unremarkable. For the next 6years the patient exhibited only mild deterioration of his balance and in addition developed mild rigidity affecting his limbs with no other signs of Parkinsonism. A new VPSG revealed severe PLMs with index of 141.5, mild OSA (AHI 11.5), respiratory related arousals (9/h) and violent behaviour during REM sleep (Fig. 2). In addition to ropinirole the patient received melatonin 3mg/day resulting in mild improvement of his RBD.

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Fig. 2. Night polysomnography, 30s epoch. Montage: EOG (left-A2, right-A1), EEG (F3-A2, F4-A1, C3-A2, C4-A1, O1-A2, O2-A1), EMG (chin), LEGS (right+left leg in one bipolar channel), ECG, pulse, SpO2, nasal pressure, flow CU (nasal cannula), thorax abdomen (inductive plethysmography), snore CU, position. The patient moves during REM and finally falls out of bed.

3. Video sequences 

Video 1:Abnormal behaviour during REM sleep. The patient punches, kicks and finally falls out of bed.

Video 2:An almost rhythmic, 1–2Hz oscillation of the posterior soft palate characteristic of symptomatic palatal tremor. However, some of the movements are clearly myoclonic in nature and the term palatal myoclonus probably better describes the movement disorder in this case.

4. Discussion 

Palatal tremor (syn. palatal myoclonus) is a rare movement disorder subdivided into essential (EPT) and symptomatic (SPT) forms [1]. EPT is a syndrome of unknown aetiology in which there is typically isolated rhythmic movements of the anterior soft palate often associated with ear clicks which can be heard by the patient [1]. SPT is characterized by rhythmic oscillation of the posterior soft palate accompanied by other signs and symptoms mainly of brainstem origin. Definable aetiologies for SPT most commonly include monophasic structural lesions such as stroke, trauma, demyelination and posterior fossa tumors [2]. However, up to 17% of all SPT cases emerge in the spectrum of a neurodegenerative process [2]. In these cases there are prominent signs and symptoms of cerebellar and/or brainstem dysfunction, and they form a heterogeneous syndrome, the so called “syndrome of progressive ataxia and palatal tremor” that is considered by some authors a distinct neurodegenerative disorder [2], [3]. In all reported cases of PAPT there is no information regarding sleep related disorders. In the case we present, the appearance of idiopathic RBD 2 years prior to PAPT emergence turns the diagnosis towards a synoucleinopathy [4]. The combination of idiopathic RBD, followed by cerebellar and extrapyramidal dysfunction, can be encountered in MSA. The MRI of the brain was negative both times but was performed early in the course of the disease. The VPSG both times reveals REM sleep without atonia accompanied by aggressive behaviour, PLMs and mild OSA – a combination that is prevalent in MSA [5]. However, the absence of autonomic dysfunction after 6-year follow-up is against the diagnosis of MSA.

The authors report no possible conflicts of interest or sources of financial support.