The Differential Diagnostic Value Of Near Response In Patients With Prolonged Disorders Of Consciousness

Background: Behavioral assessment is the current gold standard of differential diagnosis in prolonged Disorders of Consciousness(pDOC),i.e.Minimally Conscious State(MCS,a state with impaired and fluctuated consciousness)and Unresponsive Wakefulness State(UWS,a state with no consciousness).Behavioral assessment relies on examiner's subjective inference of patients' voluntary movement which may reduce its diagnostic accuracy.The pupillary response of near response(NR)is a classic smooth muscle behavior which occurs in response to a near stimulus.Previous studies suggest NR may have a relationship with voluntray attention which is a conscious activity.Objective: The aim of this study was to investigate whether voluntary attention was necessary to NR and the differential diagnostic value of NR in pDOC patients.Methods: The investigation of the relationship between NR and voluntary attention was conducted by using two commands,i.e.Command A: watch the stimulus;Command B: keep looking forward but do nothing,to manipulate healthy subjects' voluntary attention in the NR assessment.In pDOC patients,only Command A was used.We performed repeated Coma Recovery Scale Revised(CRS-R)in one week to determine the baseline states of consciousness of pDOC patients.The diagnostic accuracy of NR was measured by using the baseline conscious states as the criterion.Resting state electroencephalography was recorded in patients to improve the reliability of the diagnostic results.Global relative alpha power was chosen as the target EEG characteristic.Results: 20 healthy subjects and 20 pDOC patients(4 EMCS,8 MCS and 8 UWS)were recruited in this study.Note that we also included patients with Emergence from Minimally Conscious State(EMCS,a state with relative high consciousness level and severe disability)as pDOC patients due to their closed relationship with pDOC.All healthy subjects showed NR under Command A,whereas no one showed NR under Command B(p ? 0.05).Eleven(11/12,92%)MCS/EMCS patients and 3(3/8,38%)UWS patients showed NR.The sensitivity and specificity of NR in differentiating conscious patients(MCS/EMCS)from UWS was calculated as 92% and 63% respectively.The global relative alpha power of UWS patients with positive NR(0.1558 ± 0.01)was significantly higher than UWS patients with negative NR(0.1165 ± 0.02)(p = 0.036).The difference of global relative alpha power between UWS patients with positive NR and MCS/EMCS patients(0.1558 ± 0.02)was not significant(p = 0.734).Conclusion: Our results suggest voluntary attention is necessary for the occurrence of NR and NR is a promising tool of differential diagnosis in pDOC patients.