Abstracts

Rationale: Pattern sensitivity can be diagnosed by presenting series of visual patterns to the subject in the EEG laboratory; however, testing for pattern sensitivity is not routinely done during EEG recording. This work aimed to highlight the incidence of pattern sensitivity among patients referred for routine EEG recording during a one year period, identifying the cause of referral, diagnosis, and demographic characteristics of pattern sensitive patients. Methods: All patients four years old and above, who had no motor or visual impairment, referred for routine EEG during 12 months period and whose parents agreed to be enrolled in the study were included. EEG was recorded using 21-channel Stellate Harmonie Digital EEG. Intermittent photic stimulation and pattern sensitivity were tested for each case. Pattern sensitivity was tested by scanning three different rhythmically moving patterns (figure 1) at reading distance with the patient seated in illuminated room. Pattern evoking a paroxysmal response was reintroduced after exposure to a blank white card to confirm the findings. Results: Two hundred twenty eight patients were studied, their ages ranged from four to twelve years. Twelve patients (5.26 %) had pattern sensitivity, their ages ranged from 5 to 12 years (median 8.9 years), 8 were females and 5 were males with a female to male ratio 1.6: 1. Nine (75%) were referred for seizure disorder; 2 had idiopathic photosensitive epilepsy, 2 had juvenile myoclonic epilepsy, 3 had childhood absence epilepsy and 1 had eyelid myoclonia with absences. Two were referred with the diagnosis of migraine, one with headache and poor scholastic performance and one with recurrent attacks of dizziness for investigation. Seven of the twelve patients (58.3%) had a previous EEG done without testing for pattern sensitivity. Eight patients (66.6%) were born to consanguineous parents; five (41.6%) had positive family history for epilepsy, three (25%) for migraine and two (16.6%) for migraine and epilepsy. Two of the three patients with childhood absence epilepsy were twins. Epileptiform discharges provoked by pattern stimulation were generalized in eight (66.6%) and were in the form of building up posterior discharge that was unilateral in one patient and was then generalized in three. Two patients (16.6%) had pattern sensitivity without photosensitivity. Three patients had ictal clinical phenomena during pattern stimulation, a brief absence with eye blinking in two and with facial twitching in one. Seven reported subjective symptoms as nausea, dizziness, articulation difficulty and headache during pattern stimulation. Conclusions: Diagnosis of pattern sensitivity is often missed as it is not routinely tested for during EEG recording. The result of the study challenges the concept about the consistent association between photosensitivity and pattern sensitivity, it also raises the question about the incidence of pattern sensitivity among children who do not suffer from epilepsy and in particular those with headache/ migraine, dyslexia and scholastic difficulties; further studies are therefore needed to clarify the phenotypic spectrum of this EEG trait.