From the FDA:
Genentech and FDA notified healthcare professionals about a third case of progressive multifocal leukoencephalopathy [PML], the first case of PML in a patient with rheumatoid arthritis [RA] treated with Rituxan who has not previously received treatment with a TNF antagonist. Information to date suggests that patients with RA who receive Rituxan have an increased risk of PML.
Physicians should consider PML in any patient being treated with Rituxan who presents with new onset neurologic manifestations. Consultation with a neurologist, brain MRI, and lumbar puncture should be considered as clinically indicated.
More at: http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm187791.htm