The influence of racial and environmental factors on EEG photoparoxysmal responses in Zimbabwe.

OBJECTIVE: This study examined the influences of environmental and racial factors on the incidence of EEG photoparoxysmal responses (PPRs) to intermittent photic stimulation (IPS) in a multi-racial population exposed to seasonal variations in sunshine intensity. MATERIALS AND METHODS: The records of patients referred for EEG examination in Harare, Zimbabwe were screened for the presence of PPRs to IPS. The age, sex and racial classification of patients manifesting PPRs were studied. The relationship between sunshine duration and intensity and the frequency of PPRs was also studied. RESULTS: EEG records of 16,496 patients referred for EEG examination were studied. Of these, 136 patients (0.8%) showed PPRs to photic stimulation. The highest age-specific PPR (2.0%) occurred in the 16-20 year age group. The race-specific PPRs were 1.5% for white patients, 1.18% for Asian patients, 0.36% for colored patients and 0.09% for black patients (chi3[2] = 95.21, P = 0.001). The incidence of PPRs did not show any significant variation with the mean monthly sunshine duration (P = 0.8254) or with the mean monthly sunlight radiation (P = 0.2631). CONCLUSION: The findings of this study support a role for genetic rather than environmental factors in the relative rarity of PPRs in black Zimbabweans.