Rationale:
The taxonomy of the epilepsies has at times been controversial, but many patients can be easily typed into focal epilepsy, in which seizures are conceptualized to consistently arise from lateralized regional networks, vs. generalized epilepsy in which seizures arise in broad, bilaterally mostly synchronous networks. While the critical circuitry of all generalized seizure types remains unclear, thalamocortical network hyperexcitability often appears to be a critical network component. Patients with reticulothalamocortical epilepsies commonly have spike- or polyspike-wave runs at specific frequencies while those with focal epilepsy commonly have ictal patterns that evolve in frequency and morphology. Most prolonged ictal patterns have the potential for excitotoxicity if untreated, while absence and myoclonic-absence seizures seemingly do not. While focal EEG patterns with a spike wave appearance have been reported, we question if focal reticulothalamocortical seizures are possible.
Methods:
We did a frequency analysis of prolonged epileptiform runs in a difficult to classify case of a right-handed female in her forties with clinical seizure onset post-partum, consisting of unilateral eyelid and facial twitching for 2-20 minutes, sometimes minor confusion as well as a single convulsion. Events seemingly resolved until recurrence during and after a second pregnancy. The only potential risk factor identified was HELLP syndrome during the third trimester of the first (but not second) pregnancy. EEGs revealed many hours of long runs of temporal and diffuse spikes and spike wave patterns as described below, despite being clinically seizure free on levetiracetam 2500 mg twice daily and lamotrigine twice daily. MRI and neuropsychological testing were normal, although FDG PET revealed slight bitemporal hypometabolism.
Results:
In a 48-hour ambulatory EEG, electrographic seizure-like patterns lasted a total of approximately 24 hours (see features in Figure 1), without clinical seizures. The frequency bands of these patterns generally ranged between 3-4.5 Hz. Persyst spectral power analyses also illuminated prominent components at 6-9 Hz that are likely supraharmonic frequencies. Power of the 3-9Hz band in time series was therefore contrasted to a control frequency range of 0-1 Hz, as the latter was not a marker of epileptiform discharges. During seizure-like periods and compared to the control, the 3-9 Hz range generally had significantly higher power and without evolution, which was consistent throughout these periods (Figure 2).
Conclusions:
The true nature of the epileptogenic network remains uncertain, however, the lack of clinical and radiographic excitotoxicity despite hours-long runs of ictal-appearing temporal discharges in combination with generalized spike and polyspike wave patterns raises the hypothesis of a unique epileptiform generator with some similarity to absence and myoclonic-absence seizures that often activates only regionally. Continued surveillance of her mesial temporal structures, memory, mood as well as genetic testing may further illuminate this case.
Funding: None