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

Abstract

Objective: This study aimed to identify early clinical, magnetic resonance imaging (MRI), and electroencephalographic (EEG) characteristics of neuronal ceroid lipofuscinosis type 2 (CLN2) disease to enable early diagnosis, thus providing the key to early treatment, and optimized care and outcomes.

Methods: Retrospective clinical chart review of a series of patients diagnosed with CLN2 disease from 2005 to 2015 at a single center in Italy. Clinical, MRI, and EEG findings were reviewed.

Results: A total of 14 patients were included. For the whole group, median (range) age at disease onset was 3.0 (2.0-3.8) years. Epilepsy was the most commonly reported presenting symptom (in 50% [seven of 14] of patients), occurring at the age of 3.2 (2.6-3.8) years. First seizure was myoclonic in 36% (five of 14) of patients, followed by generalized tonic-clonic in 29% (4 of 14), atonic in 22% (three of 14), and focal with motor signs in 14% (two of 14). All patients walked independently at the age of 12.0 (11.0-18.0) months, but delayed speech or regression of acquired verbal skills was present in 100% of patients at 3 years. EEGs revealed a photoparoxysmal response (PPR) on intermittent photic stimulation in 93% (13 of 14) of patients. PPR was present from the first EEG, which was performed at 3.6 (3.1-4.0) years, in 43% (six of 14) of patients; it was documented at low (1-3 Hz) stimulation frequencies in 69% (nine of 13) and took the form of a flash-per-flash response in 69% (nine of 13). First brain MRI at the age of 3.8 (3.0-5.1) years revealed cerebellar atrophy in 100% (14 of 14) of patients and alteration of the periventricular white matter signal in the posterior hemispheric region in 79% (11 of 14).

Significance: Early photosensitivity (typically PPR at low stimulation frequencies of 1-3 Hz) is a hallmark of CLN2 disease. This diagnosis should be considered in a child presenting with any type of seizure, and particularly if it is accompanied by delayed speech and/or ataxia or MRI abnormalities (posterior white matter signal alteration or cerebellar atrophy).

Keywords: CLN2; Intermittent photic stimulation; Late infantile neuronal ceroid lipofuscinosis; Neuronal ceroid lipofuscinosis; Photoparoxysmal response.