What characterizes infantile spasms on an EEG?

Infantile spasms, also known as West syndrome, are characterized by specific electroencephalographic patterns. The distinguishing feature on the EEG during these spasms is the presence of electrodecremental events, which are seen as a sudden, transient loss of electrical activity that corresponds with the spasms occurring in the infant. This activity manifests as a notable attenuation or slowing of the background rhythm, often accompanied by bursts of voltage changes.

Electrodecremental events are significant indicators of the underlying pathology in infantile spasms and demonstrate how the brain's electrical activity changes during the spasms. This feature helps differentiate infantile spasms from other seizure types and is essential for accurate diagnosis and management.

The other choices, such as focal sharp waves, FIRDA (frontal intermittent rhythmic delta activity), and subclinical spike waves do not predominantly characterize infantile spasms on an EEG. While these may be seen in other types of seizures or neurological conditions, they lack the distinct pattern associated with the electrodecremental events that are characteristic of infantile spasms.