The Food and Drug Administration is investigating a reported case of the brain infection progressive multifocal leukoencephalopathy in a patient taking the Novartis MS drug Gilenya in Europe. The regulator announced the investigation Thursday and said in a statement that this is the first case of PML reported in a Gilenya patient who has not taken Biogen Idec’s Tysabri, which the regulator notes has been associated with a higher risk of PML.

The FDA says the patient’s treatment protocol included using Gilenya after previous treatments which included interferon beta-1a and azathioprine. The FDA says it is working with Novartis.

Novartis told MM&M in an email that that it has reviewed the information and “considers that several features in this case of PML make it unlikely to be attributable to Gilenya.” The company says expert MRI reviewers found the lesions with PML before treatment with Gilenya started and the lesions were “atypical and could not exclude PML.” The drug maker also notes the previous treatments the patient had before beginning treatment and the “relatively short 7-month exposure to Gilenya.” Novartis also notes that 71,000 patients have received the drug with no prior reports of the condition.

The FDA approved Gilenya in 2010, and the market has been a contentious once since the FDA approved Biogen Idec’s Tecfidera in March. ISI Group analyst Mark Schoenebaum called Tecfidera’s debut the “holy mother of all launches,” in July. Sales have been so strong that Biogen raised its guidance for the year.

Novartis has been working to keep its drug top-of-mind, though efforts such as its “Hey, MS, Take This!” campaign that featured empowered, adolescents, adding verve instead of sympathy. Payers have also been stand-offish: BioTrends Research Group noted this month that many insurers have pushed the drug into a step-therapy protocol, requiring patients fail at a lower-level treatment before approving a Tecfidera prescription.

PML is caused by the John Cunningham virus, which damages myelin, a protein and fat sheath that surrounds nerve fibers. The FDA says PML usually causes death or disability.