Electroencephalographic abnormalities in aseptic meningitis and noninfectious headache. A comparative study

Background.-The finding of abnormalities on electroencephalogram (EEC) duri ng the course of aseptic meningitis is often considered to be indicative of parenchymal brain involvement, even in absence of clinical signs of enceph alitis. Objective.-To investigate if patients with aseptic nonherpetic meningitis w ho have abnormal EEG recordings during the acute stage of the disease diffe r in clinical characteristics or cerebrospinal fluid findings from patients with aseptic meningitis and normal EEC recordings. Methods.-The EEG records of 82 patients with aseptic meningitis were review ed, A. comparative group consisted of 41 age-matched patients with severe h eadaches without evidence of meningeal inflammation. Results.-Significantly more patients with aseptic meningitis (28%) demonstr ated abnormalities on EEG than controls (12%) (P=.048), Patients with asept ic meningitis and abnormal EEG findings (n = 23) did not differ in age, dur ation of symptoms, clinical course, cerebrospinal fluid cell count, or prot ein level from those with normal EEG findings (n = 59), However, all patien ts with aseptic meningitis who were confused (n = 5) also revealed EEG abno rmalities (P<.00012). Patients with headache with normal EEG recordings did not differ from those with abnormal EEGs in age, sex, or duration of symptoms. Nevertheless, pat ients with common migraine (n = 9) showed abnormalities on EEG (P=.06) more frequently. Conclusions.-The finding of an abnormal EEG in patients with aseptic mening itis, clear mental state and absence of focal neurological signs should not be used as proof of encephalitis, Because pathological examination is usua lly not performed, it remains unclear if EEG abnormalities in patients with aseptic meningitis indicate a silent parenchymal inflammation, or reflect an infectious encephalopathy.