Mismatch negativity and late auditory evoked potentials in comatose patients

The purpose of this study was to assess the patterns of mismatch negativity (MMN) and N100 component in comatose patients and to evaluate their prognostic value vis-à-vis return of consciousness.

MMN and auditory (early, middle-latency and late) evoked potentials were recorded in 52 normals and in 128 comatose patients (comas due to neurosurgical and neurological problems). At the time of recording, all patients scored lower than 8 on the Glasgow scale.

Visually detected N100 and MMN were confirmed by cross-correlation of sub-averages. The MMN was present in 33/128 patients and the N100 component in 84/128. The amplitudes of MMN and N100 waves detected in comatose patients were statistically different from those of normal subjects. By 3 months after the onset of coma, 95 patients had returned to consciousness, most of them with moderate to severe disability. A ratio of 30/33 patients with MMN and 70/84 with N100 had regained consciousness. The presence of a MMN together with a N100 component was more specific (90.9%) than the presence of a N100 component irrespective of MMN (57.6%) in terms of predicting return to consciousness, but its sensitivity was lower (respectively 31.6% for MMN and 73.7% for N100). The mean period that elapsed between the recording of evoked potentials and a return to consciousness was 6.3+/-4 days. MLAEPs were also highly specific, but BAEPs were not.

MMN and auditory evoked potentials provide a reliable assessment of the functional status of comatose patients. When present, MMN and the N100 differ from those found in normal subjects in terms of latencies and amplitudes. As a predictor of return of consciousness MMN had high specificity and low sensitivity, whereas the N100 had high sensitivity and low specificity. This study demonstrates that the recording of MMN and the auditory N100 can be a very useful aid in the assessment of coma and in predicting whether or not a patient will regain consciousness.