Given that November is National Epilepsy Awareness Month, it seemed fitting to explore some of the less common, but still interesting seizure types. Of the 1 in 10 people who experience a seizure during their lifetime, 1 in 26 will develop epilepsy. This paper reviews some of the syndromes known as reflex seizures. Even those who’ve been in the EEG field a while may not be aware of these less-known seizure syndromes. This is a very brief overview of Chapter 13: Reflex Seizures and Reflex Epilepsies, from the book The Epilepsies: Seizures, Syndromes and Management, written by CP Panayiotopoulos, MD, PhD, FRCP.
Reflex seizures occur at a prevalence of 4-7% amongst patients with epilepsy, and are determined by their specific precipitating stimulus and the clinical/EEG response. The stimuli may be simple (such as a flash of light) or complex (such as reading or arithmetic).
Perhaps one of the more sensationalized reflex seizures is VGS – Video-game induced seizures. About 2/3 of VGS are accounted to patients with idiopathic occipital lobe epilepsy, but the seizure-provoking mechanism is unknown. Interestingly, these patients are generally not photosensitive in the EEG laboratory, but have spontaneous occipital spikes in their resting EEG.
Pattern-sensitive epilepsy (striped clothes, wallpaper or furnishings, venetian blinds, A/C grills and radiators) refers to seizures induced by patterns, but is not a particular epileptic syndrome. This type of seizure is closely related to photosensitivity (the seizure or abnormality that can arise in response to intermittent photic stimulation).
FOS – fixation-off sensitivity is elicited by elimination of central vision and fixation (producing high-amplitude occipital or generalized paroxysmal discharges). FOS is often suggested in the routine EEG by abnormalities that consistently occur only when the eyes are closed. Scotosensitive abnormalities are seizures that are elicited by the complete absence of retinal stimulation by light. Pure scotosensitive patients are rare.
Startle-induced seizures are elicited by a sudden and unexpected stimulus, typically a sudden noise. Habituation to repetitive stimulation does occur. I remember the first time I had a patient with a startle-induced response; the noise was accidental but the response from the patient (on her EEG) was memorable! Startle-induced seizures tend to be more common in patients with Down’s syndrome, but also are seen in patients with localized or diffuse static brain pathology, typically occurring within the first 2 years of life.
Among the more complex Reflex Epilepsies are Thinking-induced seizures – these occur in response to high cognitive functions, such as mathematical calculations, drawing, chess, or working a Rubik’s cube. Typically, these occur in the context of idiopathic generalized epilepsy, and most patients may also suffer from spontaneous seizures. These have been demonstrated neuropsychologically to right parietal cortical dysfunction.
Reading Epilepsy is another fascinating syndrome, typically manifested by myoclonic jerks of the jaw while reading, with a typical age of onset of 10-19 years. If the patient continues to read after the initial manifestations, this may lead to a spread to trunk and limb muscles. Reading epilepsy may be an inherited syndrome. Diagnostically, it is rare to find any abnormalities aside from the EEG in this type of syndrome, and the interictal EEG is usually normal.
For a more exhaustive discussion about these and other reflex epilepsies, please check out the book!
Panayiotopoulos CP. The Epilepsies: Seizures, Syndromes and Management. Oxfordshire (UK): Bladon Medical Publishing; 2005. Chapter 13, Reflex Seizures and Reflex Epilepsies. Available from: https://www.ncbi.nlm.nih.gov/books/NBK2596/
Written by: Cheryll Poissant, REEGT/EPT, MI/OP