Actigraphy assessments of circadian sleep-wake cycles in the Vegetative and Minimally Conscious States
1 Brain and Mind Institute, University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7, Canada
2 Coma Science Group: Department of Neurology and Cyclotron Research Centre, University Hospital and University of Liège, Allée du 6 août n° 8, Sart Tilman B30 - 4000, Belgium
3 Cognition and Brain Sciences Unit, Medical Research Council, 15 Chaucer Road, Cambridge, CB2 7EF, UK
BMC Medicine 2013, 11:18 doi:10.1186/1741-7015-11-18
See related commentary here http://www.biomedcentral.com/1741-7015/11/19Published: 24 January 2013
The Vegetative and Minimally Conscious States (VS; MCS) are characterized by absent or highly disordered signs of awareness alongside preserved sleep-wake cycles. According to international diagnostic guidelines, sleep-wake cycles are assessed by means of observations of variable periods of eye-opening and eye-closure. However, there is little empirical evidence for true circadian sleep-wake cycling in these patients, and there have been no large-scale investigations of the validity of this diagnostic criterion.
We measured the circadian sleep-wake rhythms of 55 VS and MCS patients by means of wrist actigraphy, an indirect method that is highly correlated with polysomnographic estimates of sleeping/waking.
Contrary to the diagnostic guidelines, a significant proportion of patients did not exhibit statistically reliable sleep-wake cycles. The circadian rhythms of VS patients were significantly more impaired than those of MCS patients, as were the circadian rhythms of patients with non-traumatic injuries relative to those with traumatic injuries. The reliability of the circadian rhythms were significantly predicted by the patients' levels of visual and motor functioning, consistent with the putative biological generators of these rhythms.
The high variability across diagnoses and etiologies highlights the need for improved guidelines for the assessment of sleep-wake cycles in VS and MCS, and advocates the use of actigraphy as an inexpensive and non-invasive alternative.