The utility of the electroencephalogram in the evaluation of patients presenting with headache: a review of the literature.

Electroencephalography has traditionally been considered a useful adjunct to the clinical evaluation of headache. We performed a literature review to determine whether evidence supports the routine use of the electroencephalogram (EEG) for patients with headache. After excluding case reports, case series in which subjects were selected because of abnormal EEGs, abstracts with insufficient information for analysis, and reviews without original data, we found 40 articles describing EEG findings in headache patients. These articles dated from 1941 to 1994. We compared these articles against six criteria established to determine the validity of data evaluating the utility of a diagnostic test. These criteria were (1) a comparison against established diagnostic criteria, (2) the use of appropriately matched controls, (3) a study setting that minimizes biases, (4) a blinded interpretation of the EEGs, (5) a sensible interpretation of the abnormalities observed, and (6) the replicability of the techniques used. One article met all six literature criteria, three articles met five criteria, 11 met four, nine met three, seven met two, seven met one, and two met none. The only abnormality consistently reported in headache patients, as opposed to controls, in studies of relatively nonflawed design was a prominent photic driving response at high flash (the "H-response"). The H-response was less effective than clinical criteria in distinguishing patients with headaches from individuals without headaches and in distinguishing migraine from other headache types. Studies did not show that the EEG is an effective screen for structural causes of headache, nor does the EEG effectively identify headache subgroups with different prognoses.(ABSTRACT TRUNCATED AT 250 WORDS)