Antinuclear antibodies in patients on anticonvulsant therapy.

Antinuclear antibodies to calf thymus nuclei, NP, DNA, sDNA, sNP and Sm antigen were investigated in sera from 170 patients on various programmes of prolonged anticonvulsant treatment. Findings were compared to those on 214 tuberculous patients on isoniazid, 109 SLE patients and 66 healthy subjects. Patients on anticonvulsants had a significantly higher incidence of ANA to DNA, sDNA, sNP and Sm antigen than the controls but had a lower incidence of ANA to all antigens, except sNP, than the SLE patients. Patients on isoniazid did not have DNA antibodies, but had antibodies to whole nuclei and to NP which were practically absent in the anticonvulsant group. Of all patients on anticonvulsants only those receiving hydantoins had ANA to Sm antigen, while those receiving only primidone had antibodies to sNP but no antibodies to DNA. Alteration of sNP with isoniazid did not result in an increased incidence of ANA in the anticonvulsant group as it does in isoniazid treated subjects. It is concluded that the SLE-activating properties of diverse anticonvulsants probably resides in their potential to induce ANA. Although all anticonvulsants elicit ANA directed primarily to sNP, each may do so by different mechanisms or by altering different sites in the sNP molecule. The mechanisms by which anticonvulsant and isoniazid intake results in ANA probably differ. Presence of DNA antibodies in some patients on anticonvulsants may indicate that their convulsions were due to SLE.