Demyelinating optic neuritis presenting as a clinically isolated syndrome

Clinically isolated syndrome (CIS) describes a single, first-occurrence attack caused by inflammation/demyelination in 1 or more locations in the central nervous system. The optic nerve is a frequent site affected by this neurologic event. As the name implies, CIS is an isolated condition but is often considered a precursor to multiple sclerosis (MS). When distinctive brain lesions detected by magnetic resonance imaging (MRI) accompany CIS, the person is considered at a high risk for MS. Treatment is aimed at delaying the onset of a second neurologic episode, reducing the accumulation of MRI-detected brain lesions and delaying the development of definite MS. This article describes a 40-year-old woman who experienced a sudden loss of vision in the right eye. Testing ultimately found a normal MRI, demyelination of the optic nerve, and progressive thinning of the retinal nerve fiber layer, leading to a diagnosis of CIS.