With dimethyl fumarate, the risk appears to disappear – although this isn’t confirmed – when JC antibody–positive patients are taken off the drug, and their lymphocyte counts fall below 500 per mcL, Dr. Berger said.
“Unfortunately for fingolimod, we don’t have a defined risk-mitigation strategy,” he said. However, researchers have noticed that the fingolimod cases have occurred more often in older people, possibly because of the aging of the immune system, he said.
Another three MS drugs – alemtuzumab (Lemtrada), ocrelizumab (Ocrevus; with rituximab as proxy), and teriflunomide (Aubagio; with leflunomide as proxy) have unknown risk, according to Dr. Berger. There have been three cases in ocrelizumab (rituximab as proxy) and one in teriflunomide (leflunomide as proxy), but all were carry-overs from natalizumab or fingolimod exposure or occurred after natalizumab exposure.
What can physicians do if a patient develops PML? Stopping the drug and restoring the immune system is crucial, he said.