FIRDA (frontal intermittent rhythmic delta activity)

• Frontal
• Intermittent: In cycles, so not continuous
• Rhythmic: Repetition of a waveform with relatively uniform morphology and duration, without an interval between consecutive waveforms.
• Delta: Delta waves
• Activity

• The FIRDA can be more specified with the prevalence, duration, frequency, amplitude, stimulus-induced (SI), Evolving OR Fluctuating (both terms refer to changes in either frequency, location or morphology).
• If a more ictal appearance it can be categorized as FIRDA+:
  • +F: superimposed fast activity.
  • +S: superimposed sharp waves or spikes, or sharply contoured.
  • +FS: superimposed fast activity and sharp waves or spikes, or sharply contoured.

Clinical relevance:

• Often due to global cerebral dysfunction (e.g. metabolic-, toxic- encephalopathy, traumatic)
• FIRDA is rarely due to a subcortical dysfunction/lesion (e.g. lewy body dementia) or elevated intracranial pressure.
• A small amount of FIRDA, especially when it is restricted to drowsiness, can be a normal in elderly or children.

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FIRDA in a 70 year old male (source)

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Notes