From the Guidelines
OIRDA on an EEG refers to Occipital Intermittent Rhythmic Delta Activity, which is a pattern characterized by bursts of rhythmic delta waves that appear predominantly in the occipital regions of the brain. This pattern is most commonly seen in children and adolescents with absence epilepsy, though it can occasionally be observed in other epilepsy syndromes as well. According to the American Clinical Neurophysiology Society definitions used in the discussion by the task force 1, rhythmic and periodic EEG patterns that do not meet criteria for electrographic seizures are of unclear significance in patients who are comatose after cardiac arrest. The ictal-interictal continuum, which includes patterns such as OIRDA, is considered to be possible seizure or status epilepticus even without fulfilling strict electrographic criteria 1. Some key points to consider when interpreting OIRDA on an EEG include:
- The presence of OIRDA may indicate cortical hyperexcitability in the occipital regions, which may reflect underlying thalamocortical network dysfunction that contributes to the generation of absence seizures.
- The clinical significance of OIRDA is still unclear, and its treatment is largely based on clinical correlation and the presence of other epileptiform abnormalities.
- The use of antiseizure medications, such as ethosuximide, valproic acid, or lamotrigine, may be considered in patients with OIRDA, especially if they exhibit clinical absence seizures 1. It is essential to note that the treatment of OIRDA should be individualized and based on the patient's specific clinical presentation and EEG findings, as the current evidence is limited, and the optimal treatment approach is still uncertain 1.
From the Research
OIRDA Meaning on EEG
- OIRDA stands for Occipital Intermittent Rhythmic Delta Activity, a pattern seen on electroencephalograms (EEGs) 2, 3, 4, 5.
- It is characterized by a symmetric sinusoidal occipital-maximal activity, often associated with childhood idiopathic generalized epilepsies 2.
- OIRDA can be lateralized or maximal on the hemispheric side ipsilateral to the more defining epileptiform discharges in focal epilepsies 2.
- It may exhibit a notched morphology due to the intermixed sharp wave activities, although the sharp waves are not occurring repetitively 2.
- OIRDA is highly correlated with epilepsy, particularly in children, and is rarely associated with acute encephalopathy 4, 5.
Clinical Correlation
- Studies have shown that OIRDA is present almost exclusively in children and is associated with epilepsy, including generalized tonic-clonic seizures and absence seizures 5.
- The presence of OIRDA may suggest a cortical origin of the activity, as opposed to a subcortical generator in patients with primary generalized absence epilepsy 2.
- OIRDA can be induced by eye closure, and its presence may provoke clinicians to delve further into a diagnostic workup 3.
EEG Features
- OIRDA is typically characterized by a high-amplitude, saw-toothed pattern with a mean frequency of 2.89 +/- 0.50 Hz 5.
- It is often reactive to eye opening and can be generalized or lateralized 5.
- The incidence of epilepsy in patients with OIRDA is significantly higher than in control subjects, particularly in those with generalized tonic-clonic seizures and absence seizures 5.