EEG Frequency Analysis in Conversion and Somatoform Disorder

Patients with "hysterical" neurologic symptoms have long puzzled neurologists and psychiatrists. "Hysteria" has recently been subdivided into conversion and somatoform disorder. We applied computerized EEG frequency analysis to 10 patients with diagnosed conversion disorder, 10 somatoform disorder patients, and 10 control subjects. One minute EEG samples composed of 4 sec epochs were recorded from left frontal (F7-C3), right frontal (F8-C4), left posterior (T5-01) and right posterior (T6-02) derivations. Spectral power was calculated for 4 bands (0.25-4HZ, 4.25-8Hz, 8.25-13Hz, and 13.25-30Hz), and for the full frequency range. Low (0.25-8Hz) and high (8.25-30Hz) frequency bands were compared to determine high/low power ratios on the left and right (PHLL) and (PHLR), ratios of left/right front (PLRF) and posterior (PLRP) power, mean alpha frequency deviation frontally (FLRF) and posteriorly (FLRP), and mobility of left and right frontal power (MOLF and MORF). No significant differences were found between conversion disorder patients and controls in PHLL, PHLR, PLRP, and MORF. PLRF, FLRF and MOLF differed significantly between patients and controls. Power and frequency ratios of right frontal mobilities suggested a decrease in high frequency power, reduction in mean alpha frequency, and lower predominant frequency in the right frontal area in somatoform disorder patients as compared to controls, but significance was not reached. Somatoform and conversion disorder patients differed significantly in these spectral measures. These observations suggest that the two "hysterical" disorders may have distinct pathophysiology, and may be due to eventually identifiable cerebral dysfunction in some cases.