Pattern sensitivity: a missed part of the diagnosis

Pattern sensitivity can be diagnosed by presenting a series of visual patterns to the subject in the electroencephalography (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 1-year period, identifying the cause of referral, diagnosis, and the characteristics of pattern-sensitive patients.

All patients aged 4 years and older who were referred for routine EEG during a 12-month period and had no motor or visual impairment were enrolled in the study. Intermittent photic stimulation and pattern sensitivity were tested for each case. Pattern sensitivity was tested by scanning three different rhythmically moving patterns at reading distance with the patient seated in an illuminated room. A pattern evoking a paroxysmal response was reintroduced after exposure to a blank white card to confirm the findings.

Two hundred twenty-eight patients were studied; twelve patients (5.26%) had pattern sensitivity and their ages ranged from 5 to 12 years. Eight of these patients (66.7%) were referred for seizure disorders, 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. Five patients (41.6%) had positive family history for epilepsy, three (25%) for migraine, and two (16.6%) for migraine and epilepsy. Two patients (16.6%) had pattern sensitivity without photosensitivity. Pattern stimulation provoked epileptiform discharges in eight patients (66.6%), focal discharges in one, and unilateral build-up of posterior discharge in three.

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 of a consistent association between photosensitivity and pattern sensitivity; it also raises questions about the incidence of pattern sensitivity among children who do not suffer from epilepsy and in particular those with migraine, headache and scholastic difficulties. Further studies are therefore needed to clarify the phenotypic spectrum of this EEG trait.