Systemic Prognosis

It is classically held that optic neuritis is less likely to lead to MS in children than in adults.317 In adults, Rizzo and Lessell460 reported that 58% of optic neuritis patients (69% of women and 33% of men) were diagnosed as having MS during an average follow-up of 14.9 years. The incidence of MS following childhood optic neuritis has ranged from 5.2 to 55.5% in different studies.295,317,460 There seems to be a greater predisposition for children with unilateral rather than bilateral optic neuritis to develop MS.222,317,460 Conversely, optic neuritis is commonly reported in studies of children with MS; in a recent report by Bye et al,73 all five children with MS had this early sign. Because the incidence of MS continues to increase with long-term follow up in adults with optic neuritis, and the length of follow up is less than 15 years in most pediatric studies, one cannot conclude on the basis of present data that the incidence of demyelinating disease is less in children with optic neuritis than in adults.

Kriss et al317 found that MS developed in 3 of 29 children with bilateral optic neuritis and 3 of 10 children with unilateral optic neuritis, suggesting that, while bilateral cases have a lower incidence of MS than unilateral cases, the risk in bilateral cases is not negligible (Table 3.8). In the 8 of 30 patients from the Kennedy and Carroll series294 who developed MS, four had simultaneous bilateral disc swelling. In the Riikonen study,458 MS developed in seven of eight patients with unilateral optic neuritis and in only 2 of 13 patients with bilateral optic neuritis. Riikonen noted that all patients who later developed MS had a second attack of optic neuritis within 1 year of the first attack.

Systemic Evaluation of Pediatric Optic Neuritis

The diagnosis of bilateral optic neuritis is established by the finding of bilaterally decreased vision, decreased color vision, an afferent pupillary defect (if the visual loss is asymmetrical), swollen or normal discs, and the absence of

Table 3.8  Incidence of MS in unilateral versus bilateral childhood optic neuritis

space-occupying intracranial lesions, such as optic nerve glioma, craniopharyngioma, or hydrocephalus, on MR imaging. Using kinetic perimetry, cecocentral scotomas and large central scotomas are the most common visual field defects.

Once the diagnosis of optic neuritis is established, a diagnostic evaluation is undertaken to determine an underlying cause (Table 3.9). The MR imaging is exquisitely sensitive to the periventricular ovoid lesions that characterize MS in adults.60 In the Optic Neuritis Treatment Trial,38 unenhanced MR imaging of the brain was performed as part of baseline diagnostic testing with a standardized protocol in 440 adults. The MR images in 418 of these patients were deemed acceptable for evaluation of signal intensity abnormalities. At the 2-year follow up, the initial MR imaging findings were compared with the neurologic course in each patient to determine whether any association could be established. Results of this study showed initial MR imaging findings to be a powerful predictor of MS.416 At 15 years, 25% of patients with no lesions on baseline MRI developed MS during followup compared with 72% of patients with 1 or more lesion.416 After 10 years, the risk of developing MS was very low for patients without baseline lesions, but it remained substantial for those with lesions. In patients without lesions, baseline factors associated with a lower risk for MS included male sex, optic disc swelling, and atypical features of the optic neuritis. These findings are consistent with results of the earlier study by Morrissey et al393 which suggested that, with long-term follow up, the risk of developing MS may approach 100% in adults with abnormal MR images, whereas the risk in patients with normal MR images is likely to remain low. Evidence from the Riikonen study459 suggests that MR imaging may be as useful in children as it is in adults for predicting which patients will subsequently develop MS.

In children, a lumbar puncture is usually performed to rule out elevated intracranial pressure, meningitis, leukemia,

Table 3.9  Infectious and noninfectious causes of childhood optic neuritis