Brief potentially ictal rhythmic discharges (BIRDs) are a unique EEG pattern that shares some characteristics with seizures but does not fulfill the full criteria required for seizure classification. These discharges are important because of their potential to evolve into a full seizure and their association with poor clinical outcomes, particularly in critically ill patients.

Characteristics of BIRDs

  • Duration: BIRDs last for less than 10 seconds, which is why they don't meet the duration criteria for a seizure (typically ≥10 seconds).
  • Evolution: These discharges exhibit a rhythmic, evolving pattern that mimics ictal (seizure-like) activity. They can be seen as rhythmic spikes or sharp waves that increase in frequency or amplitude during the event.
  • Location: The discharges can localize to one specific area of the brain or spread to neighboring regions. For example, left temporal BIRDs can spread into the left parasagittal or subtemporal regions, indicating potential involvement of wider cortical networks.
  • Pattern: The discharges may have a spike-wave pattern or rhythmic bursts of high-frequency activity. While the discharges are often rhythmic, they can be quite variable in their frequency and morphology.

Clinical Significance

  • Association with Seizures: Although BIRDs themselves do not meet the clinical criteria for seizures, they are highly predictive of seizure onset. Studies show that more than 90% of patients with BIRDs will go on to experience a full seizure, typically within hours to days.
  • Critical Illness: BIRDs are commonly seen in critically ill patients, particularly those with acute neurological insults, such as:
    • Brain tumors: New, developing tumors can create cortical irritability that leads to BIRDs.
    • Strokes: Areas of the brain affected by ischemia or infarction may exhibit BIRDs as a sign of impending seizure activity.
    • NMDA receptor encephalitis: This autoimmune condition, which targets NMDA receptors in the brain, is often associated with BIRDs.
    • Neonates: In premature infants or those with brain injury, BIRDs can be seen as part of the neurological instability.
  • Severe Outcome: The presence of BIRDs is associated with poor outcomes, including a high risk of progression to status epilepticus or long-term seizure activity. This makes BIRDs an important marker for immediate intervention.

Diagnosis and Treatment

  • Identification on EEG: Identifying BIRDs involves recognizing the evolving, rhythmic discharges on EEG that are shorter than 10 seconds but still exhibit seizure-like patterns. These discharges can involve the temporal lobes or other regions of the cortex, and their spread to surrounding regions can help with localization.
  • Management: Although BIRDs are not classified as seizures, they warrant prompt treatment due to their high likelihood of evolving into a full seizure. Treatment typically involves:
    • Antiepileptic drugs (AEDs): Given the high risk of progression to seizures, AEDs are administered as a prophylactic measure. First-line AEDs such as levetiracetam, valproate, or phenytoin may be used, depending on the clinical scenario and patient characteristics.
    • Monitoring: In critically ill patients, continuous EEG monitoring is often necessary to detect any further evolution of BIRDs into seizures and to assess the effectiveness of treatment.
    • Treat underlying cause: If BIRDs are associated with an acute neurological event, such as a tumor or stroke, addressing the underlying cause (e.g., surgical intervention, thrombolytics for stroke) is also important for improving patient outcomes.

Conclusion

While BIRDs do not meet the strict clinical criteria for seizures, they are a significant EEG finding that should not be ignored. Their high predictive value for the development of seizures and their association with poor outcomes make them an important marker for early intervention. Prompt recognition and treatment of BIRDs can help prevent seizures and improve patient prognosis, especially in critically ill individuals.