Echographic and electrophysiologic examinations in endocrine orbitopathy

Endocrine orbitopathy (EO) is the most frequent cause of compressive optic neuropathy (CON). The posterior thickening of the superior rectus, the medial rectus and the superior oblique muscles causes such optic nerve compression. The increased apical compression of the optic nerve results in Graves-related optic neuropathy The aim of this study was to correlate the echographic measurements of the medial rectus thickness with visual evoked potentials (VEP) in 17 patients with EO. Eleven patients suffered from long-standing EO, six patients had acute EO. Each patient had a visual acuity of 20/20 in both eyes. Medial rectus thickness was evaluated in the frontal section using contact A/B-mode echography performed with an Ultrascan Digital B instrument with a 10 MHz probe. The VEPs were evoked by pattern reversal stimulation and they were monopolarly recorded over the Oz site. The VEPs were abnormal when the thickness of the medial rectus muscle was increased in cases of long-standing EO. The echographic and electrophysiological data were not correlated in cases of acute EO. We suggest VEPs be recorded when a thickened medial rectus is detected by ultrasound in patients with EO, because VEPs can reveal the presence of dysthyroid optic neuropathy (DON).