The dynamics of neuronal dysfunction and recovery following severe head injury assessed with serial multimodality evoked potentials

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✓ Serial studies of visual, auditory, and somatosensory evoked potentials (EP's) obtained from 139 severely head-injured patients up to 1 year after trauma were analyzed to ascertain whether or not EP's can be used to monitor neurological recovery or deterioration following secondary insults. The EP data were analyzed using a grading system of abnormality developed previously, and patients were grouped by the most severe EP abnormality found in any modality during an early study (mean Day 3). The findings showed differential recovery trends depending on the severity of EP abnormality obtained on the initial study and presence of secondary insult. If EP's were normal early after injury, they remained so for up to 1 year, and these patients did well clinically. The EP's that were absent did not improve, and the patients had poor outcomes. Secondary insults did not affect the EP's or the outcomes of patients in these two groups. When EP's that were initially mildly abnormal became normal or remained no worse than mildly abnormal, patients had favorable outcomes in spite of complications. In contrast, deterioration of EP's with secondary insult indicated poor patient outcome. Severe EP abnormalities which improved over time led to favorable outcomes. However, persistence or deterioration of severe abnormalities indicated a poor outcome. Changes in EP's over time were better indicators of outcome than the presence or absence of complications. The results suggest that EP's may be used to assess neural recovery and the consequences of secondary insults to the brain. Four case reports are included to exemplify results.

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Address for Ms. Hyatt: University of Virginia Medical School, Charlottesville, Virginia.

Address reprint requests to: Pauline G. Newlon, M.S., Division of Neurosurgery, Box 631, MCV Station, Medical College of Virginia, Richmond, Virginia 23298.

© AANS, except where prohibited by US copyright law.

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Figures

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    Left: Incidence of change in evoked potential grades comparing responses recorded initially (mean Day 3) and serially up to 1 year after trauma. Graphs are grouped data (MEP) and individual modalities. Colors indicate grade of abnormality observed in the early study. Stars indicate impossibilities (such as, normal potentials cannot improve). Numbers above the bars are the actual numbers of patients in each group. MEP = multimodality evoked potential; SER = somatosensory cortical evoked response; VER = visual cortical evoked response; BAER = brain-stem auditory evoked response. Right: Individual MEP results recorded at four time intervals after injury. Colored roman numerals and connecting lines denote the MEP grade group determined by the initial study. Grade I and IV MEP's do not change over time, whereas Grades II and III show both improvement and decline. The majority of Grade II responses improve to Grade I, although rates of recovery differ. A small percentage of patients in this group show neuroelectric deterioration. In the Grade III group, equal numbers of responses recover and deteriorate.

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    Case 1. Recordings from a patient who suffered a mass lesion and cardiac failure secondary to head injury. Evoked potentials (EP's) obtained from one side only are illustrated in this and all subsequent figures when responses were similar bilaterally. On Day 3 after injury, responses were, at worst, mildly abnormal and consistent with recovery. The brain-stem auditory evoked response (BAER, not shown) was Grade I. Following development of a mass lesion and a hypotensive episode (Day 6), cortical EP's had deteriorated in complexity. Brain-stem function remained normal (BAER, Day 6). By Day 9, after a period of prolonged uncontrollable hypotension, no activity could be recorded from any modality.

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    Case 2. On Day 1, the presence of the second positive wave in the left hemisphere (not apparent on the right) is important. The appearance of this wave on the left indicates integrity of primary cortical function. However, by Day 5 the right hemisphere already shows evidence of the return of primary cortical function, although diminished in amplitude. Note the differences in recovery rate of the two hemispheres. The more severely compromised right hemisphere, the side from which the mass lesion was removed, takes a matter of months to recover fully whereas the left side approaches normal within 2 weeks after injury.

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    Case 2. The auditory brain-stem response recorded on Day 1 only is shown, but this response was normal on each occasion. The visual evoked response was initially mildly abnormal, but showed increasing complexity upon repeated evaluation.

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    Case 3. Serial recordings obtained from a patient with sustained elevated ICP. The early study (Day 1) showed mildly abnormal cortical (somatosensory and visual evoked response and normal brain-stem auditory (BAER) function. Follow-up studies revealed transient cortical compromise at Day 111 which recovered to some extent later (Day 246). However, the BAER from serial studies on Days 14, 111 (not shown), and 246 indicated significant compromise of brain-stem function.

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    Case 4. A Day 2 study revealed mild to moderate cortical dysfunction and normal brain-stem transmission (BAER, Grade I). A good to moderate outcome was expected. Additional studies performed on Days 13 and 83 showed cortical neuroelectric improvement with the reappearance of longer latency components, even though the patient had developed serious complications and was neurologically unchanged. Brain-stem function remained normal. He eventually recovered and on Day 289, his evoked potentials were entirely normal.

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