A 31-year-old woman comes to the office because of a 3-day history of "fogginess" and decreased color perception in her right eye. She also reports a dull, aching pain behind the eye that worsens with eye movement. She has no significant medical history but mentions a brief episode of unexplained numbness in her left leg that resolved spontaneously last year. On physical examination, visual acuity is 20/100 in the right eye and 20/20 in the left eye. When a penlight is moved from the left eye to the right eye, the right pupil appears to dilate. Funduscopic examination is unremarkable.
Which of the following is the most appropriate next step in the management of this patient?
The correct answer is:
C) MRI of the brain and orbits
This patient is presenting with a classic case of optic neuritis, characterized by subacute, monocular vision loss, decreased color vision, and pain with eye movement. The pupillary finding described is a relative afferent pupillary defect (RAPD) or Marcus Gunn pupil, which is a hallmark of optic nerve disease. In a young patient, optic neuritis is frequently the first clinical manifestation of multiple sclerosis (MS). The most appropriate next step is an MRI of the brain and orbits with gadolinium to confirm the diagnosis of optic neuritis, which would show enhancement of the optic nerve, and to look for white matter lesions (demyelinating plaques) that would suggest a diagnosis of MS and help predict the risk of future episodes.
Answer choice A: Intravenous methylprednisolone, is incorrect. While high-dose IV corticosteroids are the treatment for an acute episode of optic neuritis to speed the rate of visual recovery, the diagnosis and risk stratification via MRI should be prioritized. Furthermore, corticosteroids do not affect the ultimate long-term visual outcome.
Answer choice B: Lumbar puncture, is incorrect. While the presence of oligoclonal bands in the cerebrospinal fluid can support a diagnosis of MS, an MRI is more sensitive and is the preferred initial imaging modality to demonstrate dissemination in space and time.
Answer choice D: Oral prednisone, is incorrect. The Optic Neuritis Treatment Trial (ONTT) demonstrated that low-dose oral prednisone alone actually increases the rate of recurrent optic neuritis compared to placebo or IV steroids. Therefore, standard oral prednisone is avoided in the acute management of this condition.
Answer choice E: Visual evoked potentials, is incorrect. This test measures the electrical response of the brain to visual stimuli and can detect subclinical involvement of the optic nerve. However, it is less specific than MRI and is generally reserved for cases where the diagnosis remains unclear after imaging.
Key Learning Point
Optic neuritis presents as subacute monocular vision loss, pain with eye movement, and a relative afferent pupillary defect (RAPD). Because it is highly associated with multiple sclerosis, the initial management should include an MRI of the brain and orbits to assess for demyelinating plaques and to determine the risk of progression to MS.
