OPTIC GLIOMAS IN NEUROFIBROMATOSIS TYPE-1 - ROLE OF VISUAL-EVOKED POTENTIALS

Optic gliomas occur in 15% of patients with neurofibromatosis type 1 ( NF 1) and are a significant cause of morbidity. Of these tumors, 20-30 % become symptomatic, usually before age 10 years. Previous studies ha ve suggested that visual evoked potentials (VEPs) are a sensitive meth od for the detection of asymptomatic optic gliomas. Because routine ne uroimaging of children with NF 1 is currently not recommended, the rol e of pattern-shift VEPs (PS VEPs) as a screening test for optic glioma s was evaluated. PS VEPs were performed on 10 children with NF 1 and o ptic gliomas and 20 children with NF 1 and normal visual pathways (as defined on MRI). PS VEPs had 90% sensitivity for detecting optic gliom as, with an increase in sensitivity to 100% when hemifield stimulation was used. The specificity of the test was 60%. Four of 20 children wi thout optic gliomas had thickened optic nerves on computed tomography which represented dural ectasia with normal visual pathways on MRI; PS VEPs were normal in these patients. The efficacy of PS VEPs as a rout ine screen for optic gliomas is limited by the age at which children w ill cooperate with the test procedure and the high incidence of false- positive results; however, VEPs do provide a useful adjunct to routine clinical ophthalmologic assessment in the detection of optic gliomas in children with NF 1. Abnormal test results provide a stronger indica tion for neuroimaging. The early detection of optic gliomas allows for close monitoring of tumor progression and earlier intervention prior to significant visual loss.