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Photosensitive epilepsies and pathophysiologic mechanisms of the photoparoxysmal response

From the National Epilepsy Center, Shizuoka Higashi Hospital, Shizuoka, Japan.

Address correspondence and reprint requests to Dr. Y. Takahashi, Department of Pediatrics, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8076, Japan.

OBJECTIVE: To identify the pathophysiologic mechanisms of the photoparoxysmal response (PPR) in various photosensitive epilepsy syndromes, and to discuss the relation between these pathophysiologic mechanisms and the classification of epilepsies and epileptic syndromes.

BACKGROUND: The authors found two types of pathophysiologic mechanisms of PPRs (wavelength-dependent PPRs and quantity-of-light–dependent PPRs) in patients with idiopathic generalized epilepsy and hereditary dentatorubral-pallidoluysian atrophy.

METHODS: Intermittent photic stimulation with wavelength-specific optical filters was performed in photosensitive epileptic patients: six patients had severe myoclonic epilepsy in infancy (SMEI), eight had localization-related epilepsy (LRE), and seven had symptomatic generalized epilepsy (SGE).

RESULTS: Four of the six photosensitive SMEI patients had quantity-of-light–dependent PPRs. Five of the eight photosensitive LRE patients had wavelength-dependent PPRs. Four of the seven photosensitive SGE patients had wavelength-dependent PPRs, and two had quantity-of-light–dependent PPRs.

CONCLUSIONS: The type of pathophysiologic mechanism for eliciting PPRs by low-luminance photic stimulation was closely related to the classification of the epilepsy syndrome.

Key words: Photoparoxysmal response—Severe myoclonic epilepsy in infancy—Localization-related epilepsy—Wavelength dependency.

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