Progressive multifocal leukoencephalopathy in systemic lupus erythematosus treated with pembrolizumab.

This case report discusses a patient with systemic lupus erythematosus (SLE) treated with low-dose azathioprine who developed progressive multifocal leukoencephalopathy (PML). PML is a rare, severe, demyelinating disease linked to John Cunningham polyomavirus (JCV) reactivation.Treated with pembrolizumab, an immune checkpoint inhibitor, the patient initially improved. However, after the fourth dose, her condition rapidly worsened resulting in treatment discontinuation and death. Similar cases highlight the complex interplay of factors in PML development in SLE patients, including immunosuppression and genetic factors. The use of pembrolizumab in PML and SLE necessitates careful consideration of potential complications.