Summary

A 69-year-old Caucasian woman with a 15-year history of refractory chronic lymphocytic B-cell leukaemia (CLL), treated with alemtuzumab in the past 10 months presented with a subacute right foot drop. Initial evaluation with a brain CT scan, lumbosacral MRI, nerve conduction studies and LP was negative. In the following months, progressive right hemibody weakness and dysarthria developed. Brain MRI showed a bilateral parasagittal frontal lesion. Alemtuzumab treatment was withdrawn. Progressive multifocal leukoencephalopathy (PML) was confirmed by PCR. Attempted antiviral therapies proved fruitless. Inexorable clinical deterioration ensued and the patient passed away 10 months after the presentation. This case report intends to call attention for PML as a potential fatal complication of severe immunosuppression, including the possible role of new monoclonal antibodies (such as alemtuzumab) in its pathogenesis.