Complications of immunosuppression associated with weekly low dose methotrexate.

Complications of immunosuppression are thought to be rare with the use of low dose pulse methotrexate (MTX) for nonneoplastic conditions. We describe 4 complications of immunosuppression observed in a group of 41 patients who had received MTX for at least 6 months, during a 2-year period. We report the first case of a reversible lymphoproliferative disorder similar to that reported with immunosuppressive therapy associated with organ transplantation. Two cases of disseminated herpes zoster and 1 case with Pneumocystis carinii pneumonia are described. As the indications for the use of low dose MTX broaden and older patients with other comorbid diseases are included, our experience suggests that complications of immunosuppression with prolonged use of MTX may be seen more commonly.