[Intrathecal IgG synthesis: when is determination of oligoclonal bands necessary?].

Two quantitative methods of determining the intrathecal synthesis of IgG were tested for their usefulness in deciding about the necessity of further investigations of oligoclonal bands (OCB) in the CSF. For this purpose, in 2003 patients with various neurological diseases the intrathecal synthesis of IgG was determined by Reiber's formula and by the IgG index, as well as by the demonstration of OCB by isoelectric focusing (IEF). While OCB could be detected in no patient with an IgG index < 0.45, these bands were always demonstrated in patients with an index > 0.80. Even though arrange of 0.45-0.8 OCB was only detected in 268/1316 patients (20.4%), in 190/268 samples (70.8%) OCB were the only criterion for intrathecal synthesis of IgG. Calculation of intrathecal synthesis of IgG by Reiber's formula was less helpful in deciding about the necessity for IEF. Even though they had no intrathecal synthesis of IgG, as calculated by Reiber's formula, 189/1472 patients (12.8%) had OCB in the CSF. OCB were always detected if local production of IgG was > 12%. In patients with a severe damage of the blood-CSF barrier, calculation of the IgG index gave more false-positive results than calculations using Reiber's formula.