Diagnosis: Optic neuritis in the setting of Multiple Sclerosis
Optic neuritis (ON) occurs due to inflammation of the optic nerve. This can occur due to a variety of reasons including infectious, inflammatory, idiopathic, and demyelinating diseases (e.g., multiple sclerosis, neuromyelitis optica). ON is the first sign of mulitple sclerosis (MS) in a quarter of cases, and occurs at some point for the majority of individuals diagnosed with MS. Similar to MS, studies have shown higher rates of ON in individuals who live at higher latitudes and those of northern European ancestry.
The classic presentation of ON generally involves a young woman, with subacute (hours-days) onset of painful, monocular visual disturbance. The visual defects can include sudden vision loss, color blindness, blurry vision, or a central scotoma, and can present with periorbital pain. Color vision defects, including loss of color vision and color desaturation, are a common identifying feature of ON. A relative afferent pupillary defect (RAPD), generally tested with a swinging flashlight test, is usually present.
After a thorough physical exam, the next step to definitively diagnose ON in this patient would be to get an MRI brain and orbits to evaluate for demyelinating lesions. Other secondary diagnostic mechanisms for ON include visual evoked potentials, optical coherence tomography, and CSF examination.
Much of today’s knowledge and guidelines on ON are built on the seminal work of The Optic Neuritis Treatment Trial (ONTT) published in 1992. The trial’s study population was 77% female averaging 32 years, with an average duration of visual symptoms for 5 days before entering the trial. The ONTT helped pave the understanding of ON predicting the development of clinically definite MS. Following a first ever episode of ON, the five year incidence of clinically definite MS was 30%, increased to a cumulative incidence of 50% at 15 years irrespective of brain scans. With regards to imaging, 72% with an abnormal brain scan developed MS after 15 years, while just a quarter of those with normal scans were diagnosed with MS. The McDonald MRI criteria allow for a diagnosis of MS in some patients experiencing first attacks of ON if imaging demonstrates disease with dissemination in space and time.
IV corticosteroids provide symptomatic relief and research shows they may shorten the duration of attack and can delay the onset of MS. Oral corticosteroids are not recommended. The findings of the ONTT provided evidence for the efficacy of IV steroids. Notably, those who received IV methylprednisolone (IVMP) followed by oral prednisone gained their vision back sooner than those who received oral prednisone alone. This group suffered fewer attacks of recurrent ON than the oral prednisone group, who actually suffered more attacks than the placebo group, suggesting increased risk of ON after oral steroids alone (27% oral prednisone vs. 15% placebo vs. 13% IVMP). In addition, the IV steroid group appeared to gain temporary protection against developing clinically definite MS within two years, showing a lower rate of diagnosis (7.5% IV steroids vs. 14.7% oral steroids). The oral prednisone group showed similar outcomes to the placebo group in terms of vision recovery and vision outcomes at six months.
References and Additional Resources:
1. “EyeWiki: Demyelinating Optic Neuritis.” Available at: https://eyewiki.aao.org/Demyelinating_Optic_Neuritis.
2. Toosy AT, Mason DF, Miller DH. Optic neuritis. The Lancet Neurology. 2014;13(1): 83-99.
3. Bennett JL. Optic Neuritis. Continuum (Minneap Minn). 2019;25(5):1236–1264.
4. Beck RW, Cleary PA, Anderson MM, et al. A randomized, controlled trial of corticosteroids in the treatment of acute optic neuritis. New England Journal of Medicine. 1992;326:581-588.
5. Newman NJ. The Optic Neuritis Treatment Trial. Ophthalmology. 2020;127(4):S172-S173.
Neuro-oph Case 3 Index