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

Background. - The finding of abnormalities on electroencephalogram (EEG) during the course of aseptic meningitis is often considered to be indicative of parenchymal brain involvement, even in absence of clinical signs of encephalitis. Objective. - To investigate if patients with aseptic nonherpetic meningitis who have abnormal EEG recordings during the acute stage of the disease differ in clinical characteristics or cerebrospinal fluid findings from patients with aseptic meningitis and normal EEG recordings. Methods. - The EEG records of 82 patients with aseptic meningitis were reviewed. A comparative group consisted of 41 age-matched patients with severe headaches without evidence of meningeal inflammation. Results. - Significantly more patients with aseptic meningitis (28%) demonstrated abnormalities on EEG than controls (12%) (P= .048). Patients with aseptic meningitis and abnormal EEG findings (n = 23) did not differ in age, duration of symptoms, clinical course, cerebrospinal fluid cell count, or protein level from those with normal EEG findings (n = 59). However, all patients with aseptic meningitis who were confused (n = 5) also revealed EEG abnormalities (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, patients with common migraine (n = 9) showed abnormalities on EEG (P= .06) more frequently. Conclusions. - The finding of an abnormal EEG in patients with aseptic meningitis, clear mental state and absence of focal neurological signs should not be used as proof of encephalitis. Because pathological examination is usually not performed, it remains unclear if EEG abnormalities in patients with aseptic meningitis indicate a silent parenchymal inflammation, or reflect an infectious encephalopathy.