Clinical correlates of frontal intermittent rhythmic delta activity (FIRDA)

Objectives To investigate the clinical correlates of frontal intermittent rhythmic delta activity (FIRDA). Methods we prospectively assessed all EEG studies recorded in our center over 3 months for the presence of frontal intermittent rhythmic delta activity (FIRDA). The FIRDA group was compared with a randomly selected control group from among EEGs recorded during the same period. Comparisons among FIRDA and non-FIRDA groups were performed using uni- and multi-variate analyses. Results We found 36 patients with FIRDA among 559 EEG recordings (6%); the control group consisted of 80 subjects. While epilepsy was more frequent in the control group, structural brain lesions and encephalopathy were independently associated with the occurrence of FIRDA, but we could not identify any specific etiology. Asymmetric FIRDA was associated with an underlying brain lesion. Occasionally, FIRDA was recorded in otherwise healthy subjects during hyperventilation. Conclusion FIRDA appears more common than previously reported, and is associated with a wide range of lesions and encephalopathic conditions. Significance FIRDA occurrence should prompt investigations for toxic-metabolic disturbances and for structural lesions (particularly if asymmetric), but does not suggest an epileptic predilection.