Unique Characteristics of the Photoparoxysmal Response in Patients With Neuronal Ceroid Lipofuscinosis Type 2

Abstract

Photoparoxysmal responses in patients with neuronal ceroid lipofuscinosis type 2 have features which are distinguishing from photoparoxysmal responses seen in other epilepsies.

Photosensitivity is an early marker of neuronal ceroid lipofuscinosis type 2 disease

“…17,18 In the large series of 34 patients with CLN2 disease studied by Jadav et al, 17 for example, only two patients were reported to have PPR at 9 and 15 Hz, but it is unclear how IPS was performed and whether this was carried out in all patients. 13,15 A reduction in the size of evoked discharges is reported to occur at frequencies of 4 Hz or higher, and PPR is sometimes accompanied by muscle twitches in the limbs and/or face. 4 Another study conducted in 18 patients with CLN2 disease using standardized EEG reported a large polyspike response to a single flash of light (evoked by IPS) in all patients in whom this test was performed, 13 but again it is unclear how many patients underwent IPS.…”

“…Ambient lighting was minimized (to approximately 50 lux), but was sufficient to facilitate observation of the patient while controlling ocular fixation on the center of the lamp and to note any subtle clinical ictal phenomena. Separate trains of flashes of 5-s duration were used at the following frequencies: 1,2,6,8,10,12,13,14,15,16,17,18,19,20,25,30,40,50, and 60 Hz. Flash trains were separated by a pause of at least 7 s. IPS was used to assess the lowest (starting at, and increasing from 1 Hz) and highest (starting at, and decreasing from 60 Hz) frequencies evoking a generalized PPR.…”

“…Separate trains of flashes of 5-s duration were used at the following frequencies: 1, 2, 6,8,10,12,13,14,15,16,17,18,19,20,25,30,40,50, and 60 Hz. The international 10-20 system of electrode placement was used to record EEGs.…”

“…10 Early attempts to improve the diagnosis of CLN2 disease suggested that electroencephalography (EEG) might represent a sensitive diagnostic approach, [11][12][13] but this approach was abandoned with the appearance of specific molecular and enzymatic diagnostic methods. 15 Although a PPR is most commonly reported at low IPS frequencies in CLN2 disease, it has also been reported at middle and high frequencies. One EEG feature known to indicate an NCL diagnosis is a photoparoxysmal response (PPR), a paroxysmal spike-wave response, to intermittent photic stimulation (IPS), which involves flashing light on and off for a set duration at escalating frequencies.…”

“…The PPR is generally seen in the patient's initial EEG; the spike-wave response is time locked to the photic stimuli, and the response occurs at low-frequency IPS (1-3 Hz). 15 Although a PPR is most commonly reported at low IPS frequencies in CLN2 disease, it has also been reported at middle and high frequencies. 16 It would be beneficial if PPR features could be used as a marker for NCLs, as EEGs are performed for all patients who present with seizures, whereas other tests (e.g., visual evoked potential, electroretinography, and electron microscopy) are not performed unless NCLs are suspected.…”