Follow-up studies of somatosensory evoked potentials and auditory brainstem evoked potentials in patients with post-coma unawareness (PCU) of traumatic brain injury

Abstract

Some patients who suffer severe traumatic brain injury (TBI) fail to recover higher brain functions in spite of giving the appearance of sleep-wake cycles. Such a state is called post-coma unawareness (PCU) and varies in type and degree. Patients may remain in this state for months or even years. This study focused on the follow-up of upper-limb somatosensory evoked potential (USEP) measurements and auditory brainstem responses (ABR), with an emphasis on dynamic changes, in 10 patients with PCU resulting from TBI. The prognostic value of USEP and ABR was evaluated. Results showed that the presence of ABR in PCU patients had no prognostic value, because ABRs were found both in patients who recovered and those who did not, even a year after the trauma. The presence of normal ABR in PCU patients may suggest that the brainstem has been spared in the pathoanatomy of the PCU condition, with the significant damage occurring above this level, in cortical and subcortical (that is, hemispheral) areas. USEP was graded using the new system of Houlden [1] for ‘acute’ comatose patients. It was found that USEP measurements had some prognostic value in PCU patients. Most of the patients who remained in the PCU state had grade 2 or less initially, whereas most of the patients who later recovered or achieved at least a ‘reduced life’ state were grade 4 or more. On initial testing (when all patients were still in the PCU state), defined cortical potential (mainly in the slope of the building NI potential) was seen in only some of the patients who later recovered. No dynamic changes or signs of improvement were seen in any of the patients who did not recover (that is, who remained in the PCU state). On the other hand, dynamic changes in evoked potential (amplitude, latency and shortened latency) were found in all patients who got well and, although not homogeneous, the changes involved all the elements of normal patterns and showed a trend towards improvement. Patients who remained comatose showed no change or reduction in Houlden's grade, whereas all patients who recovered showed no change or elevation. (In one of the latter patients, the grade increased from 2 to 5.) In some patients who recovered, morphological changes in cortical potentials were seen, mainly in NI slopes.