Predicting dysthyroid optic neuropathy using computed tomography volumetric analyses of orbital structures

OBJECTIVE: To evaluate the ability of orbital apex crowding volume measurements calculated with multidetector-computed tomography to detect dysthyroid optic neuropathy. METHODS: Ninety-three patients with Graves' orbitopathy were studied prospectively. All of the patients underwent a complete neuro-ophthalmic examination and computed tomography scanning. Volumetric measurements were calculated from axial and coronal contiguous sections using a dedicated workstation. Orbital fat and muscle volume were estimated on the basis of their attenuation values (in Hounsfield units) using measurements from the anterior orbital rim to the optic foramen. Two indexes of orbital muscle crowding were calculated: i) the volumetric crowding index, which is the ratio between soft tissue (mainly extraocular muscles) and orbital fat volume and is based on axial scans of the entire orbit; and ii) the volumetric orbital apex crowding index, which is the ratio between the extraocular muscles and orbital fat volume and is based on coronal scans of the orbital apex. Two groups of orbits (with and without dysthyroid optic neuropathy) were compared. RESULTS: One hundred and two orbits of 61 patients with Graves' orbitopathy met the inclusion criteria and were analyzed. Forty-one orbits were diagnosed with Graves' orbitopathy, and 61 orbits did not have optic neuropathy. The two groups of orbits differed significantly with regard to both of the volumetric indexes (p<0.001). Although both indexes had good discrimination ability, the volumetric orbital apex crowding index yielded the best results with 92% sensitivity, 86% specificity, 81%/94% positive/negative predictive value and 88% accuracy at a cutoff of 4.14. CONCLUSION: This study found that the orbital volumetric crowding index was a more effective predictor of dysthyroid optic neuropathy than previously described computed tomography indexes were.

Neuropatía óptica distiroidea como manifestación de orbitopatía de Graves / Dysthyroid optic neuropathy: report of one case

Dysthyroid optic neuropathy is an uncommon and severe form of presentation of Graves ophtalmopathy, caused by compression and elongation of the optic nerve. Use of high dose steroids is the treatment of choice. Decompressive surgery is reserved for refractory cases. We report a 41 years old female with a dysthyroid optic neuropathy that appeared 18 years after the diagnosis of Graves disease, manifested by a marked reduction in visual acuity. Orbit CAT scan did not show compression or elongation of optic nerve. She was treated with prednisone 60 mg per day, obtaining a complete remission after 19 days of treatment. After 90 days of follow up with low doses of steroids, the patient remains asymptomatic.

Diagnostic ability of barrett's index to detect dysthyroid optic neuropathy using multidetector computed tomography

OBJECTIVES: The objective of this study was to evaluate the ability of a muscular index (Barrett's Index), calculated with multidetector computed tomography, to detect dysthyroid optic neuropathy in patients with Graves' orbitopathy. METHODS: Thirty-six patients with Graves' orbitopathy were prospectively studied and submitted to neuro-ophthalmic evaluation and multidetector computed tomography scans of the orbits. Orbits were divided into two groups: those with and without dysthyroid optic neuropathy. Barrett's index was calculated as the percentage of the orbit occupied by muscles. Sensitivity and specificity were determined for several index values. RESULTS: Sixty-four orbits (19 with and 45 without dysthyroid optic neuropathy) met the inclusion criteria for the study. The mean Barrett's index values (± SD) were 64.47 percent ± 6.06 percent and 49.44 percent ± 10.94 percentin the groups with and without dysthyroid optic neuropathy, respectively (p<0.001). Barrett's index sensitivity ranged from 32 percent to 100 percent, and Barrett's index specificity ranged from 24 percent to 100 percent. The best combination of sensitivity and specificity was 79 percent/72 percent for BI=60 percent (odds ratio: 9.2). CONCLUSIONS: Barrett's Index is a useful indicator of dysthyroid optic neuropathy and may contribute to early diagnosis and treatment. Patients with a Barrett's index >60 percent should be carefully examined and followed for the development of dysthyroid optic neuropathy.