A recent attempt to clarify the diagnosis and classification of optic neuritis (important for diagnosing other conditions with optic neuritis as an early manifestation) proposed that optic nerve T2 hyperintensity be added to the diagnostic criteria for multiple sclerosis.1 However, the results of this 3-year, single-center evaluation suggest that while optic nerve T2 hyperintensity or atrophy on MRI can be signs of optic neuritis, they may frequently be seen in association with several other conditions as well. Therefore, clinicians should be cautious before assuming a diagnosis of optic neuritis.
Study Design
This retrospective study examined the etiology of optic nerve T2 hyperintensity and/or atrophy. Over a 3-year period, investigators evaluated records from 477 patients (698 eyes) at a tertiary care center who underwent brain/orbit MRI scans (97–98% with contrast) for any reason and had a finding of optic nerve T2 hyperintensity and/or optic nerve/chiasmal atrophy in at least 1 eye. Patients were grouped into those with optic nerve T2 hyperintensity alone, those with optic nerve atrophy alone, or those with both T2 hyperintensity and atrophy, and were analyzed for the presence of conditions that could correlate with these findings.
Outcomes
Optic nerve T2 hyperintensity and/or atrophy on MRI was highly predictive of eye disease (positive predictive value 96%). The most common diagnoses overall were compressive optic neuropathy (25%), optic neuritis (22%), multifactorial (16%), and glaucoma (13%); retinopathy was only seen in 2.4% of cases. Thirty-six “clinically normal” eyes (no evidence of optic neuropathy or retinopathy on ophthalmic exam) had an abnormal optic nerve finding on MRI, and all but 9 of these eyes were retrospectively reclassified as having subclinical optic neuropathy. The specificity of optic nerve T2 hyperintensity and/or atrophy on MRI for diagnosis of optic neuritis was low at 17%, though it improved to 86% when optic nerve enhancement was also present. While optic nerve enhancement remains a strong diagnostic marker of inflammatory optic neuropathy, it was also seen in a few cases of compression, ischemia, radiation, and papilledema.
Limitations
This study does not capture every type of optic nerve abnormality on MRI or every patient with optic neuritis. For example, patients with optic nerve enhancement alone (a common finding within 1 month of acute optic neuritis onset) were not included unless there was also T2 hyperintensity and/or atrophy found.
Clinical Significance
This study shows that while T2 hyperintensity and/or atrophy on MRI are almost always clinically significant, they are not specific for optic neuritis and can be seen with other optic neuropathies or severe retinopathy. As MRI abnormalities of the optic nerve are rarely incidental or artefactual, patients with an abnormal optic nerve on MRI should have a thorough evaluation of their optic nerve and retina even in the absence of symptoms. However, optic nerve T2 hyperintensity or atrophy should not lead clinicians reflexively to a diagnosis of optic neuritis or multiple sclerosis.
Financial Disclosures: Dr. Hetal Ray discloses no financial relationships.
Reference:
1 Petzold et al. Lancet Neurology. 2022;21:1120–1134