Pattern‐sensitive Epilepsy: Electroclinical Characteristics, Natural History, and Delineation of the Epileptic Syndrome

Abstract

Purpose: To elucidate the electroclinical features and long-term outcome of patients with pattern-sensitive epilepsy. Methods: We reviewed the clinical and electroencephalo-graphic (EEG) findings of 73 (43 female and 30 male) patients in whom pattern-sensitive epilepsy was diagnosed at Mayo Clinic (Rochester, Minnesota, U.S.A.) from 1950 through 1999. We contacted patients and their relatives by letter or telephone to obtain the latest seizure and quality-of-life outcomes. Results: The median age at onset of seizures was 12.8 years (range, 0.6-32.9 years). Most patients had absence, myoclonic, or generalized tonic-clonic seizures. Interictal epileptiform discharges in the EEG were detected in 61 (83.6%) patients and were generalized in 54 (74%). Paroxysmal epileptiform discharges in the EEG elicited with standard patterns were all generalized in two thirds of patients but were restricted to the posterior head region in one-third. Eight (11%) patients did not exhibit photosen-sitivity. Television was the most common precipitant [30 patients (41%)]. Twenty-nine patients gave a clear history of one or more seizures precipitated while viewing environmental patterns such as window screens, garments, tablecloths, and ceiling tiles; the rest of the patients admitted that they preferred to avoid looking at patterned objects because these objects made them uncomfortable. The electroclinical features suggested juvenile myoclonic epilepsy in 14 patients, progressive myoclonus epilepsy in three, progressive familial cerebellar ataxia with myoclonus in two, and severe myoclonic epilepsy of infancy in one. During a median follow-up period of 15.7 years, 25 (45.5%) of 55 patients who were followed up for ≥5 years achieved complete seizure remission. The median age at remission was 24.4 years. The absence of progressive neurologic disease was correlated significantly with remission; a family history of seizures showed a trend in favor of remission. More than two thirds of the patients did not consider the seizures an impediment to their family life or to educational and occupational achievements. Conclusions: Although pattern sensitivity as a trait occurs in various epileptic syndromes, pattern-sensitive epilepsy is a readily distinguishable subtype of the visually provoked reflex epilepsies. In our opinion, the location and extent of the excitable region or regions within the visual cortex concerned with different attributes of visual function dictate susceptibility to a specific trigger (intermittent light, pattern, or color) or closely related multiple triggers and the resultant electroclinical phenomenon.

Pattern sensitivity: a missed part of the diagnosis

“…Our findings agree with Harding and Harding12 and Radhakrishnan et al4 who reported that 10% to 20% of people sensitive to pattern stimuli may be unresponsive to the conventional frequency range of intermittent photic stimulation.…”

“…However, the diagnosis of pattern sensitivity in a photosensitive patient is of clinical importance as it shows the additional range of visual stimuli to which the patient is vulnerable. Seizures in pattern-sensitive patients may be induced while viewing environmental patterns such as window screens, tablecloths, ceiling tiles, escalator steps, striped wallpaper, and clothing 1,4. Absences, often associated with eye blinking, facial contractions, and myoclonic jerks of the upper extremities, are the seizure types typically evoked by the pattern exposure 3,5.…”

Do reflex seizures and spontaneous seizures form a continuum? – Triggering factors and possible common mechanisms

“…However according to recent studies, photogenic ictiogenesis is likely to involve multiple cortical and subcortical regions beyond occipital and frontoparietal cortices that are primarily associated with vision [87,88]. The location and size of the hyperexcitable region involved may determine type and number of specific triggers that elicit a seizure [89] and establish the seizure phenotype. Albeit the causal interpretation of involved network hierarchy is arduous, a thorough investigation of the neural firing properties has started by tracking aberrant neural cortical excitability with EEG [90], MEG [84], fMRI [91] and transcranial magnetic stimulation (TMS) [83].…”

Increasing the Yield of EEG

“…Recently, Radhakrishnan et al (2005) reviewed the clinical and EEG findings of 73 patients in whom pattern sensitive epilepsy was diagnosed. This was the first study that assembled a sizable number of patients with pattern sensitivity epilepsy on the basis of their principle attributes, which was pattern induced epileptiform abnormalities in EEG and seizures.…”