The study of visual evoked potentials in patients with thyroid-associated ophthalmopathy identifies asymptomatic optic nerve involvement

In the present study we have recorded visual evoked cortical po- tentials (VECP) in 88 patients affected by autoimmune thyroid dis- ease and thyroid-associated ophthalmopathy (TAO) without clinical signs of optic neuropathy. At the time of ophthalmological examina- tion, 37 of these patients were hyperthyroid, 41 were euthyroid, and 8 were hypothyroid; 2 were not assessed. Twenty-nine normal sub- jects served as controls. We performed pattern reversal visual stim- ulation and recorded the amplitude and latency of the cortical electric response at 100 ms (P100 wave). There were no differences in the mean P100 amplitude of TAO patients and normal subjects. The mean P100 latency in patients was 105.6 0.5 ms, significantly higher than that in normal subjects (102.0 0.5 ms; P 0.00003). Latency in euthyroid patients did not differ from that in either hypo- or hyper- thyroid patients. The VECP test was positive (latency, 110.0 ms) in21 (23.8%) TAO patients. In patients with proptosis greater than 21 mm, latency was 106.7 0.7 ms, significantly higher than that in patients with normal Hertel measurements (104.3 0.6 ms; P 0.01). Latency was not increased in patients with acute inflammatory signs compared to those with inactive eye disease and in patients with altered extrinsic motility. In patients with an abnormal visual field study, the mean latency was 110.3 1.5 ms, significantly higher than that in patients with a normal visual field (104.7 0.4; by t test, P 0.000003). In conclusion, we observed a prolongation of the latency of the evoked cortical response in patients with TAO without subjective visual complaints and without optic nerve compression. We believe that the study of VECP in TAO is complementary to the study of the visual field in identifying early optic nerve dysfunction in the absence of decreased visual acuity.