Isolated idiopathic optic neuritis. Analysis of free kappa-light chains in cerebrospinal fluid and correlation with nuclear magnetic resonance findings.

There is controversy about the frequency with which patients with isolated optic neuritis (ON) subsequently develop clinically definite multiple sclerosis. Furthermore, at the time of isolated ON, there are no features that are both sensitive and accurate in predicting which patients will develop clinically definite multiple sclerosis. We analyzed cerebrospinal fluid (CSF) samples from eight patients with isolated ON and compared the result with the presence of clinically silent brain lesions demonstrated by nuclear magnetic resonance imaging. The single most common laboratory abnormality was an elevated level of free kappa-light chains in CSF. This abnormality was present in five (63%) of eight patients with isolated ON and correlated with the presence of clinically silent brain lesions demonstrated in four of the five patients by nuclear magnetic resonance. The only other laboratory abnormality that correlated with disseminated disease was the presence of oligoclonal bands, but this finding was observed less frequently than was an elevated level of free kappa-chains. Thus, the presence of free kappa-chains in CSF appears to correlate with disseminated disease in patients with isolated ON and may have prognostic value.