• neurinoma
• sleep behaviour disorder

REM sleep behaviour disorder (RBD) is a type of parasomnia described by Schenck et al.^{1, 2} It is manifested by vigorous body movements, vocalisation, and sometimes injurious behaviour occurring during vivid and violent dreams. Polysomnographic recordings show abnormal abolition of the generalised muscle atonia that occurs during REM sleep, and concurrent bursts of muscle twitching in the absence of epileptic activity.¹ There is experimental evidence^{3, 4} that the area of the brain stem, and especially the pontine tegmentum, is involved in the pathogenesis of the disorder.⁴ We report a patient who presented with RBD and was diagnosed and treated for a brain stem neurinoma.

The patient is a 59 year old man, an ex-sailor, who was referred to our clinic because of vivid dreams accompanied by violent behaviour during sleep. He described dreams during which he was trying to defend himself while he was threatened by strangers or attacked by animals. Enacting his dreams, he swore at his “enemies,” and punched and kicked his bed partner. He had repeatedly injured himself crashing into objects or falling out of bed. This aberrant behaviour had been recurring nightly over a period of six years. One year before the onset of his sleep disturbance, he had noticed impaired hearing on the left, which gradually progressed to almost complete left sided deafness.

On admission, neurological examination was unremarkable except for deafness on the left side. Routine laboratory work up—including a full blood count, electrolytes, immunoglobulins, ANA, ds-DNA, and renal, hepatic, and thyroid tests—was normal. Blood glucose was 7.65 mmol/l and serum VDRL was 2+. Brain stem auditory evoked potentials showed a mild delay of waves III–V on the left compared with the right (2.35 ms and 1.96 ms, respectively). The electroencephalogram, including 24 hour EEG monitoring, was within normal limits. Psychiatric and neuropsychological evaluations did not reveal any major psychopathology. Magnetic resonance imaging (MRI) of the brain revealed a 2.3 cm tumour in the left pontocerebellar angle compatible with a neurinoma (fig 1). Cerebrospinal fluid examination showed four white blood cells, an increased protein of 78 mg/dl (normal range 15–45), FTA-Abs 4+, FTA-Abs IgM negative, IgG 4+, VDRL negative, and TPHA positive in a dilution of 1:640. Because the patient had never been treated for syphilis, which presumably had been latent for an unknown period of time, 30 million units of a penicillin G were given daily intravenously for 10 days. A polysomnogram coupled with videotape recording was performed through the night for eight hours to evaluate the patient's sleep disorder. This showed lack of muscle atonia during most REM periods and bursts of muscle twitching of the arms and legs recorded electromyographically, in the absence of epileptic activity. These polysomnographic findings, along with the videotaped body movements, were considered pathognomonic of RBD.

The RBD was initially treated symptomatically with 1 mg clonazepam at bedtime. This resulted in a remarkable clinical improvement, beginning on the third day of treatment. About three weeks later, the tumour was surgically removed and the diagnosis of neurinoma was confirmed histologically. Following surgery, RBD manifestations completely disappeared. Subsequently, clonazepam was gradually discontinued over a one month period. At a six month follow up, the patient reported no aberrant behaviour during sleep.

The syndrome of RBD can be idiopathic or it can be a symptom of various neurological diseases. It usually affects middle aged men.² Cases of symptomatic RBD are most often associated with Parkinson's disease, multiple system atrophy, primary dementia, olivopontocerebellar degeneration, and Lewy body dementia.^{2, 5} In some of these conditions, RBD may precede other symptoms by years. To our knowledge, there has only been one previous mention of RBD being associated with tumours of the brain stem.² Our patient had a neurinoma of the left pontocerebellar angle which obviously caused his typical RBD episodes by interfering with the brain stem neuronal circuitry. As this circuitry extends bilaterally, the lesion must have affected the pontine region on both sides to cause RBD, perhaps through local oedema.

An unexpected finding in our patient was his latent syphilis, which raised the possibility of an alternative cause for RBD. Syphilis could have affected the brain stem network involved in the pathogenesis of RBD. However, we ruled out this possibility for the following reasons: first, the patient did not present with active infection, as indicated by the relevant serological and CSF findings (negative FTA-Abs IgM antibodies); second, he did not have any obvious residual clinical signs or symptoms of CNS syphilis; third, his RBD had remained relatively stable over the previous six years; moreover, the development of the tumour obviously preceded the occurrence of the abnormal sleep behaviour by at least a year, as evidenced by the presence of impaired hearing since that time; and finally, the complete remission of RBD following surgical removal of the neurinoma and the absence of any relapse during a six month follow up provides direct evidence for the aetiological association between the two conditions.

In conclusion, RBD may be symptomatic of an underlying brain stem tumour. Thus clinicians should consider the possibility of structural brain stem lesions whenever aberrant behaviour during sleep is present, even in the absence of other prominent neurological signs. A polysomnographic recording in conjunction with brain imaging studies should be performed to investigate the possibility of the coexistence of a brain tumour and RBD. Should that be the case, neurosurgical treatment is clearly indicated.

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Figure 1

A neurinoma of the left pontocerebellar angle, 2.3 cm in diameter, shown on magnetic resonance imaging of the brain (T2 weighted image).