This study examined the differences in cognitive evoked potentials in post-traumatic headache patients. The patients were 50 people with mild head injury (MHI) and headache who had: "loss of consciousness not greater than 30 minutes or no loss of consciousness; post-traumatic amnesia not exceeding 48 hours; no structural abnormalities on CT or MRI; and, Glasgow Coma Scale score of 13 or greater without subsequent deterioration." The MHI patients were matched with 20 neurologically healthy controls.
The researchers then performed EEGs on all subjects, looking specifically at P300 and N100 evoked potential amplitudes. These tests are used to measure cognitive abilities, and can detect abnormalities in dementia, cerebral dysfunction, and alterations in attention and concentration.
The study reported that "eight patients had abnormal N100 and 27 patients had abnormal P300 latencies or amplitudes." In all, 78% of the patients had abnormal test results; none of the controls had abnormalities. "Loss of consciousness [after the injury] or presence of headache and/or depression at the time of testing did not appear related to abnormalities on cognitive-evoked potentials. Medication within 24 hours of the study did not influence results."
The authors do not suggest that all cases of headache after MHI are related to brain injury. In fact, of the patients with no abnormalities on EEG tests, 90% had headaches. The study suggests that many patients with post-traumatic headache may have brain injury, but not all.
"There is still considerable controversy surrounding the post-traumatic syndrome. The general public, insurance adjusters, and even some physicians doubt the legitimacy of post-traumatic symptoms, particularly cognitive difficulties, after a seemingly 'minor' head injury. If there is a normal neurologic examination, normal head scan, and no history of actual head trauma or loss of consciousness, the questions become more pervasive. Add the complications of legal involvement and skepticism reigns, even in light of recent studies, which show little actual effect of litigation on post-traumatic symptoms or outcome."
"In summary, many patients sustaining MHI suffer from significant difficulties with concentration, memory, and/or thinking. The ability to concentrate and remember important details is often a major factor in determining an individual's ability to function in society. Sometimes these symptoms may be overlooked or disbelieved because of a 'minor' injury, no car damage, low velocity impact, and so forth. There also may be a prejudice against these patients because of legal proceedings or physician and attorney bias. Cognitive deficits may only be evident when an individual is under a great deal of stress, overtired, or trying to do more than one thing at a time. We have found that many patients are only aware of cognitive difficulty under these circumstances or when attempting to return to work or increase their activity level. These difficulties may be compounded when patients are evaluated with head imaging studies (CT or MRI) that are 'normal.' Unfortunately, a 'normal' imaging study is often considered to mean normal function."
The authors state that EEG tests of cognitive-evoked potentials "can be clinically useful in assessing and detecting cognitive dysfunction in patients sustaining mild head injury and reporting difficulties with concentration and/or memory."
Packard RC, Ham LP. Evaluation of cognitive evoked potentials in post-traumatic headache cases with cognitive dysfunction. Headache Quarterly, Current Treatment and Research 1996;7(3):218-224.