Can vestibular caloric stimulation be used to treat Dejerine-Roussy Syndrome?

Dejerine-Roussy Syndrome (thalamic pain syndrome) is characterised by the development of chronic, severe pain in the contralateral half of the body after a thalamic stroke. It is often largely refractory to treatment. In this paper we draw together a number of disparate pieces of knowledge to propose a novel therapy for this condition. There is already substantial evidence from neurological disease that the brain's left hemisphere serves to "smooth over" discrepancies in sensory input in order to impose order and maintain the existing view of the world around us. Conversely the right hemisphere acts on discrepant sensory input to cause a re-evaluation of one's world view. Based on this, it was proposed by Harris that pain is an organism's response to discrepancy. It is already known that cold water vestibular caloric irrigation of the ear leads to activation of a number of areas in the contralateral hemisphere - including the insular cortex. Indeed it is known that - presumably because it also activates the right parietal lobe - this technique can be used to treat anosognosia, somatoparaphrenia and neglect. In addition to being activated by vestibular stimulation, it has been shown that the posterior insula has a somatotopic map of the body for painful stimuli. We speculate that phylogenetically, close anatomical proximity between the pain and vestibular areas of the brain makes sense; as it would allow modulation of otherwise disabling chronic pain, when the organism makes a sudden movement to avoid a predator. Given Harris's theory we propose that post stroke thalamic pain may represent a pathological amplification of the thalamic posterior insular response to pain due to discrepant sensory input. Based on all the above we go on to hypothesise that cold vestibular caloric stimulation will be effective in treating Dejerine-Roussy Syndrome and we present provisional evidence from two patients which supports this conclusion. If our hypothesis is correct this will be the first time in clinical neurology that a chronic disorder, long considered refractory to treatment, is relieved by a simple non-invasive procedure.