eMedicine Specialties > Neurology > Seizures and Epilepsy

Reflex Epilepsy

Joseph F Hulihan, MD, Vice President, Medical Affairs, Ortho-McNeil Janssen Scientific Affairs, LLC
Contributor Information and Disclosures

Updated: Aug 27, 2007

Introduction

Background:

Reflex epilepsy is a condition in which seizures can be provoked habitually by an external stimulus or, less commonly, internal mental processes. Individuals with reflex epilepsy may have seizures exclusively in response to specific stimuli and not suffer spontaneous seizures; alternatively, reflex seizures may coexist with spontaneously occurring seizures. Reflex seizures are epileptic rather than psychogenic in nature, often manifesting epileptiform EEG changes. Reflex epilepsies may manifest as either focal-onset or primary generalized seizures.

Photosensitive epilepsy is the most common type of reflex epilepsy; seizures occur when an individual is exposed to visual stimuli, usually flashes of light of a particular frequency. In other reflex epilepsies, seizures may be provoked by auditory, olfactory, or vestibular stimuli. Reflex seizures also may occur in response to more elaborate stimuli or mental processes. Examples of these include reading epilepsy, musicogenic epilepsy, or seizures induced by cognitive processes, such as mathematical calculation.

For excellent patient education resources, visit eMedicine's Brain and Nervous System Center. Also, see eMedicine's patient education article Epilepsy.

Pathophysiology:

The immediate factors that provoke any given seizure are complex, and the occurrence of seizures in someone with epilepsy is rarely predictable. Some associations between factors that result in a general tendency for an increase or decrease in the likelihood of seizures are known, such as sleep deprivation, systemic illness, or epileptogenic drugs, but usually no immediate trigger is recognized. In contrast, reflex seizures are predictable in response to a specific stimulus.

As part of the routine EEG recording, repetitive light stimulation (photic stimulation) is administered to determine whether characteristic EEG patterns can be elicited. Production of epileptiform discharges or clinical seizures in response to photic stimulation is termed photosensitivity , and is seen in approximately 25% of patients with primary generalized epilepsy.

Animal models of genetic reflex epilepsy have been described. These include the baboon, Papio papio, in which generalized convulsions can be induced by visual stimulation. Audiogenic seizures characterize genetic reflex epilepsies in predisposed strains of mice, rats, and birds.

Reflex seizures may also be the result of acquired cerebral lesions. Photosensitivity may be induced after production of focal cortical or subcortical lesions in experimental animals. In addition, focal structural or electrographic abnormalities have been described in humans with reflex epilepsy. A child with seizures induced by bathing in hot water was found to have a left parietal malformation on brain MRI as well as epileptiform EEG discharges in that region. EEG and cerebral SPECT in a patient with musicogenic epilepsy demonstrated a right temporal focus.

Wieser has proposed a pathophysiologic model to explain the mechanism by which the triggers for reflex seizures interact with pools of susceptible neurons to generate epileptogenic brain activity or clinical seizures in susceptible individuals.

In recent years, investigators have defined some of the genetic aspects of reflex epilepsies in humans. Photosensitivity is known to be influenced by familial factors, and linkage analyses have identified potential loci for genes causing this susceptibility. In addition, children with chromosomal abnormalities have been shown to maybe have an increased tendency to photosensitivity. 

The genetics of other forms of reflex epilepsy have also been investigated. Some patients with autosomal dominant temporal lobe epilepsy — a rare, inherited form of localization-related epilepsy — may have seizures provoked by speech or other auditory stimuli. This epilepsy syndrome is associated with mutations in the gene LGI1. The inheritance and phenotypic characteristics in a family with generalized epilepsy and language-induced seizures have also been described.

Sex:

Seizures resulting from photosensitivity are more common in females; however, sex predilection of less common reflex epilepsies is uncertain.

Age:

Photosensitive epilepsy, like the majority of generalized epilepsies, generally manifests in childhood or adolescence. Other less common reflex epilepsies also tend to be described in patients of this age group.

Clinical

History:

If a history of seizures in response to specific stimuli is reported, the physician must elicit as many details as possible about the nature of the provoking stimuli. In addition, a detailed description from the patient and family members of seizure symptoms is important. Determination of whether the seizure has features suggestive of focal or generalized onset guides subsequent diagnosis and treatment.

Causes:

• Visually induced seizures may result from flickering light, removal of visual fixation or light intensity, complex visual patterns, viewing particular objects, or other visual stimuli.
  • Seizures occurring in photosensitive epilepsy are the most common type of visually induced seizures. In susceptible patients, seizures or epileptiform EEG discharges may be produced by photic stimulation during EEG recording. Seizures may also be provoked by flickering or flashing lights in the environment. Features of visual stimuli related to their epileptogenicity include flash frequency, luminance, and color of the stimulus. When clinical seizures occur, they are most often generalized seizures, either absence or myoclonic seizures that can progress to generalized tonic-clonic seizures. Alternatively, complex partial or other seizure types may occur.
  • In pattern-sensitive epilepsies, seizures are produced by particular visual patterns. These triggers may consist of circles, stripes, or other patterns, usually of high contrast. Oscillating or moving patterns are more highly epileptogenic. One case evaluated by the author is illustrative: an infant boy experienced myoclonic seizures and associated EEG discharges only when looking at a particular red hound's-tooth–pattern dress worn by his mother. In addition, the pattern needed to be slowly moved from side to side across the visual field. The pattern did not elicit the seizures when held stationary, nor did other patterns, including the same hound's-tooth pattern in black and white.
  • Seizures may be produced in some individuals by a reduction in light intensity (scotosensitive seizures) or by removal of visual fixation (fixation-off seizures). More complex visual stimuli, such as seeing particular objects, also may be a cause of reflex seizures.
  • Television and electronic screen games have been well-publicized causes of reflex seizures, particularly the mass occurrence of seizures resulting from an animated cartoon program in Japan. Epileptogenicity of such stimuli may relate to flicker frequency of the screen and distance from the viewing screen, as well as the particular visual images. European television has a lower flicker frequency than North American television (50 vs 60 cycles/second) and is therefore more epileptogenic. Photosensitivity is a causative factor for the epileptogenicity of electronic games in susceptible individuals. However, the cognitive processes involved in playing these games may also contribute to the provoked seizures. Many patients who experience their first seizure while playing electronic screen games are found to be photosensitive.
• Somatosensory stimuli, including light touch, tapping, or immersion in hot water, have been reported to be associated with reflex seizures.
  • Touch- or tap-evoked generalized seizures may occur in neurologically normal infants younger than 1 year. Seizures evoked by touch may occur as part of another condition of infancy or childhood, referred to as startle epilepsy or reflex myoclonic epilepsy. These also are primary generalized seizures. Less commonly, partial-onset seizures evoked by touch may occur, referable to a seizure focus in the sensorimotor cortex.
  • Hot water epilepsy was first described in 1945 and is more common in India than in Europe, Japan, or North America.
• Auditory stimuli are less common precipitants of reflex seizures.
  • Sounds may produce seizures in cases of startle epilepsy.
  • Audiogenic seizures have been described in many animal species and occur in commonly employed rat and mouse models of genetically determined epilepsy.
  • In humans, musicogenic epilepsy is the term for a condition in which seizures are produced by tones or music. Music-induced seizures occur as a localization-related, rather than generalized, type of seizure. The type of stimuli producing such seizures varies, and spontaneous seizures may occur in these patients.
• Reflex seizures of nonketotic hyperglycemia warrant particular mention, since these are the reflex seizures most likely to be seen by general neurologists, internists, or other medical specialists in the hospital setting. These focal, movement-induced seizures occur during nonketotic hyperglycemia and resolve with normalization of the metabolic disturbance.
• Some of the most unusual and intriguing disorders in neurology are the reflex epilepsies in which seizures are provoked by complex actions or mental processes. Examples of these include the following:
  • Primary reading epilepsy: In individuals with this condition, reading induces seizures. Jaw jerks typically occur, associated with epileptiform EEG patterns. Episodes may progress to generalized tonic-clonic seizures. Spontaneous seizures may occur, and the likelihood of seizure occurrence may increase with duration of reading or with complexity of the material being read. Processing of language within the cortex is likely to be the physiologic basis for seizure generation.
  • Seizures induced by thinking: Cognitive processes have been reported to induce seizures in susceptible persons. Initially described during the performance of mathematical calculations, the seizures also may be produced by processing spatial information or by other forms of decision making. Reflex seizures have been described as a result of playing chess or checkers, also likely due to the cognitive processes involved in playing these games.
  • Eating epilepsy: Seizures induced by eating do not comprise a specific epilepsy syndrome. Rather, eating-induced seizures occur in individuals with symptomatic localization-related epilepsy, for example, temporal lobe epilepsy. The precise causative stimulus varies. Seizures may occur at the sight or smell of food, at the beginning of eating a meal, or postprandially.
• Other complex activities that have been described as provocative factors for reflex seizures include micturition, toothbrushing, walking, and answering the telephone.

Differentials

Workup

Imaging Studies:

• Performance of neuroimaging and selection of imaging modalities should be guided by the electroclinical features of the seizures.
• Since some types of reflex seizures can occur in the context of symptomatic, localization-related epilepsy, perform brain MRI as in the evaluation of other focal epilepsies.

Other Tests:

• EEG is a critical test in the evaluation of subjects with presumed reflex epilepsy. The routine EEG should be expanded to encompass potential stimuli that evoke the patient's habitual seizures. Such testing can be performed under video monitoring if detailed characterization of clinical seizure type is needed or in cases requiring differential diagnosis or presurgical monitoring.
  • Photic stimulation is standard in the performance of EEG recordings. Stroboscopic light (photic stimulation) at various frequencies is presented to the patient. A photoparoxysmal response most often is elicited at stimulation frequencies of 15-18 cycles/second. Responses to photic stimulation include (1) photic driving, a photomyoclonic response in which myoclonic jerks are elicited synchronously with light flashes or (2) a photoconvulsive response in which clinical seizures are provoked by the light stimulus.
  • Pattern-sensitive epilepsies can be investigated in the EEG laboratory by presenting a series of visual patterns to the subject. Alternating or oscillating, black and white, and linear patterns are more highly epileptogenic than static patterns.
  • More individualized testing, often encompassing the use of detailed neuropsychological evaluation under EEG monitoring, can be employed to investigate seizures induced by thinking or other complex activities.

Treatment

Medical Care: Therapy of reflex seizures involves limiting exposure to the provoking stimulus, as well as standard epilepsy medications. Treatment with specialized lenses has shown promise for limiting seizures in patients with photosensitive epilepsy. 

Medication

When choosing antiepileptic medications, considerations are similar to those in other types of epilepsy. Electroclinical seizure type, prior treatment history, patient age, comorbidities and medication adverse effects are primary considerations.

The reader is referred to the eMedicine articles on the appropriate seizure type for a full discussion of preferred medications.

Keywords

stimulus-sensitive epilepsies, audiogenic epilepsy, eating epilepsy, hot water epilepsy, photosensitive epilepsy, photosensitivity, reflex seizures, startle epilepsy, strobe light seizures, reflex epilepsy

References

• Absence Seizures
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• Tic disorders
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• Brain and Nervous System Center
• Epilepsy Overview
• Epilepsy Causes
• Epilepsy Symptoms
• Epilepsy Treatment