Clinical and magnetic resonance imaging in optic neuritis

We found 23 of 48 patients (48%) with isolated monosymptomatic optic neuritis (ON) to have 1 to several brain lesions by MRI. All the brain lesions were clinically silent and had characteristics consistent with multiple sclerosis (MS). During 4 years of follow-up, 9 patients (19%) developed definite MS on clinical grounds. Six of the converting patients had abnormal MRIs; the other 3 had MRIs that were normal both initially (when they had ON only) and when repeated after they had developed MS. The other 17 patients with abnormal MRIs have not developed symptoms or signs of MS during follow-up. Thus, an abnormal MRI does not auger development of clinical MS within a mean of 4 years, nor does a normal MRI protect against development of disseminated disease. It is not prudent to give a patient with isolated monosymptomatic ON the diagnosis of MS (probable or definite) because of an abnormal MRI (with or without other laboratory abnormalities).