Reduced CSF IgG in patients treated with phenytoin (diphenylhydantoin)

In the CSF's from 13 out of 30 phenytoin-treated patients the IgG concentrations were lower than the lowest amont 20 controls, while only 3 out of 37 patients with brain lesions without epilepsy had so low IgG value. Titers of IgG antibodies to rabbit erythrocytes were similar in the three groups. It should be kept in mind, when evaluating results of IgG determinations in clinical neurology, that reduced IgG may be a consequence of phenytoin treatment. Reduced IgG concentrations without reduction of an antibody belonging to the IgG class indicate that the suppression of immunoglobulin synthesis by phenytoin may be selective.