Ophthalmologists commonly encounter difficulties when trying to distinguish arteritic from nonarteritic anterior ischemic optic neuropathy (AION). In this study, the authors investigated the diagnostic value of MRI of the optic nerve head for facilitating rapid identification of the underlying etiology.
Fifteen patients with confirmed giant cell arteritis-related AION (AAION) and 15 patients with nonarteritic AION (NAION) were prospectively enrolled from 2 medical centers, as well as 15 healthy controls. All subjects underwent contrast-enhanced, flow-compensated, 3-D T1-weighted MRI. The bright spot sign was defined as optic nerve head enhancement as graded by 3 masked evaluators.
The bright spot sign was found in all patients with AAION and in 7 of 15 of patients with NAION. No control patients showed signs of enhancement. Therefore, the absence of anterior optic nerve enhancement in patients with AION precluded a diagnosis of giant cell arteritis. Agreement among the 3 graders was high (k=0.815).
Small sample size limits the significance of this study. Additionally, it is not clear why optic nerve enhancement in NAION was present in some cases and not in others, or whether the signs of enhancement correlate with the degree of visual field loss or degree of disc edema. Although the results are intriguing, further study with a larger number of subjects is needed to validate the use of MRI for distinguishing between the 2 forms of AION.
There are many options for distinguishing AAION from NAION. While the gold standard is temporal artery biopsy, the procedure is invasive. Other less precise methods include lab studies (erythrocyte sedimentation rate, C-reactive protein, platelet count), fluorescein angiogram, and clinical signs and symptoms (temporal artery tenderness, scalp tenderness, headache, jaw claudication and weight loss). Pending further validation, orbital MRI could provide a fast and noninvasive alternative for differentiating AION.
American Academy of Ophthalmology