A case of progressive multifocal leukoencephalopathy in a lupus patient treated with belimumab.

Belimumab is a monoclonal antibody against soluble B-lymphocyte stimulator, an essential growth factor for B-cell maturation and activation, which was approved by the US FDA in 2011 for patients with active autoantibody-positive systemic lupus erythematosus (SLE) who have failed standard treatment. Here we present the case of a 40-year-old woman with SLE diagnosed with progressive multifocal leukoencephalopathy (PML) on belimumab. After a total of 10 infusions of belimumab, from August 2012 through April 2013, in April 2013 she developed progressive neurologic decline with episodic dystonia and autonomic symptoms. Her imaging showed multifocal, confluent regions of T2 hyperintensity in the white matter bilaterally, and CSF JCV PCR returned positive. Based on the patient's clinically mild SLE and the timing of symptom onset, belimumab likely played a key role in the development of PML. Trials of belimumab for other autoimmune diseases are ongoing; as applications for this novel drug broaden, careful monitoring for this potentially fatal adverse effect is warranted.