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Caloric vestibular stimulation is a common clinical procedure, routinely employed during testing of vestibulocochlear nerve function. The procedure involves stimulation of vestibular afferents by the application of cooled water to the tympanic membrane. Vestibular afferents are distributed widely to areas of the diencephalon and cortex, including areas believed to be involved in the regulation of mood. In accordance with these observations, imaging studies have shown widespread though largely contralateral hemispheric activation following the procedure.1
Caloric vestibular stimulation has been associated with a rapid but short lived improvement in stroke induced functional deficits,2 but the effect of the procedure on psychiatric symptomatology has not been reported. In the case described here, an improvement in manic symptoms was observed after caloric vestibular stimulation in a 29 year old woman with a 10 year history of bipolar affective disorder. The patient was admitted to an acute psychiatric ward with several weeks of increasingly elevated and irritable mood. Her symptoms fulfilled DSM-IV criteria for a manic episode. Resistance to therapeutic drug use and intolerance of side effects had limited effective management of her condition. Previous episodes of mania had often responded to ECT. At the time of admission her treatment regimen included olanzapine and carbimazole. Carbimazole had been started following the identification of abnormal thyroid function tests on routine testing.
The patient did not respond to increases in antipsychotic drugs or to a course of right unilateral ECT given three times a week. She withdrew consent for ECT when no improvement was noted after five treatments. At this point, a review of published reports suggested that left caloric vestibular stimulation might reduce the severity of the manic symptoms through modulation of mood related neural circuits. A trial was proposed and informed consent obtained. The severity of the patient’s manic symptoms was measured using the Young mania rating scale (YMRS).3 The severity of her symptoms before caloric vestibular stimulation was felt by staff to represent her general level of symptoms during the past two months.
Otological examination before the caloric stimulation revealed an intact tympanic membrane and a clear external auditory canal. A flexible tube (14 gauge) was attached to a 50 ml syringe and introduced into the left auditory canal to a depth of 2 cm; 50 ml of cold water (4°C) were then introduced into the canal over a period of two to three minutes. Run off was collected in a kidney dish. The procedure was repeated after 72 hours.
The YMRS was applied by nursing staff involved in the patient’s care at the following times: before vestibular stimulation, and at 10 minutes, 20 minutes, 60 minutes, 6 hours, 24 hours, and 48 hours after the procedure.
The procedure was well tolerated; the patient described minimal local discomfort and a sense of vertigo. Horizontal nystagmus occurred towards the right. Within two minutes of termination of the procedure the patient described a slowing of thoughts and speech and a lowered mood. She remained on the examination couch until all sensation of vertigo had passed (approximately 10 minutes). During this period she was calm, cooperative, and appropriate in behaviour. There was an obvious reduction in speed and volume of speech and a reduction in spontaneous laughter and movement. These observations corresponded to a reduction in YMRS score of 32 (pre-stimulation) to 10 (post-stimulation).
Upon returning to the ward, she remained appropriate in her behaviour and interactions with staff and other patients. The patient described a lasting lowering of mood and slowing of thoughts and quickly became embarrassed when reminded of some of the behaviours she had shown before stimulation. Staff noted a gradual increase in her manic symptoms from approximately 24 hours post-stimulation, and after 72 hours her YMRS score was similar to that observed before the procedure (fig 1). The vestibular stimulation was readministered, and a dramatic and sustained partial reduction in symptoms again occurred, followed by a slow return towards baseline.
This case describes an impressive and relatively sustained improvement in manic symptoms following left caloric vestibular stimulation. It is possible that the power of suggestion, or a “placebo” effect, contributed to the observed effect. Care was taken not to relay to the patient a sense of expectation of an improvement in mood, and extra contact with staff following the procedure was minimised. It is unlikely that the immediate improvement in symptoms reflected a change in behaviour secondary to adverse effects of the procedure. Vertigo was the only side effect experienced by the patient, and all sense of vertigo had resolved within 10 minutes of the procedure. The use of the YMRS provided a standard for comparison of the severity of her symptoms before and after stimulation and served to illustrate a marked reduction in manic symptoms.
Caloric vestibular stimulation represents a novel approach to the treatment of mania. It is possible that it exerts its effect on mood through stimulation of mood related neural circuits. Following caloric vestibular stimulation, functional magnetic resonance imaging shows widespread, mainly contralateral activation of diencephalic and cortical regions which include the basal ganglia, insula, cingulate gyrus, prefrontal, and parieto-temporal areas.1 These areas have also been implicated in disorders of mood, and some laterality of mood is suggested by neuroimaging and lesion studies that link depression to left cerebral impairment and mania to right cerebral impairment.45 Thus impulses transmitted by vestibular afferents in response to caloric vestibular stimulation may reach previously underactive neural pathways, so restoring a balance to previously imbalanced mood circuits.
Transient resolution of stroke induced deficits has been documented following caloric vestibular stimulation.2 These effects have lasted only minutes, and patients who have responded to the procedure have shown a reduced response to subsequent stimulations. The sustained response observed in this case may have been because neuronal hypofunctioning was present in the absence of overt neuronal damage as occurs following stroke.
This case report, which requires replication, describes a sustained reduction in manic symptoms following left caloric vestibular stimulation; this may have occurred through the activation of previously hypofunctioning neural circuits. Whether the observed improvement in symptoms corresponds to a normalisation of cerebral perfusion, as illustrated by positron emission tomography and functional magnetic resonance imaging, remains to be seen. Further research in the area may yield an alternative treatment for mood disorders, and provide an avenue for clarification of the neural pathways involved in the regulation of mood.
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