Progressive multifocal leukoencephalopathy or immune reconstitution inflammatory syndrome after fingolimod cessation? A case report

BACKGROUND: Fingolimod is associated with an increased risk of developing progressive multifocal leukoencephalopathy (PML); however, its discontinuation may cause severe immune reconstitution inflammatory syndrome (IRIS). As both of these conditions (especially fingolimod induced PML) are rarely described in medical case reports distinguishing between PML-IRIS and MS-IRIS may be diagnostically challenging. CASE PRESENTATION: We report a patient with severe clinical decline (Expanded Disability Status Scale (EDSS) increasing from 3.5 to 7.5) and multiple, large, contrast-enhancing lesions on brain magnetic resonance imaging (MRI) a few months after fingolimod withdrawal. The diagnostic possibilities included IRIS due to fingolimod withdrawal versus PML-IRIS. The JC virus (JCV) antibody index was positive (2.56); however, cerebrospinal fluid (CSF) JCV real-time polymerase chain reaction (JCV-PCR) was negative and brain biopsy was not performed. After a long course of aggressive treatment (several pulsed methylprednisolone infusions, plasmapheresis, intravenous dexamethasone, oral mirtazapine) the patient gradually recovered (EDSS 2.5) and MRI lesions decreased. CONCLUSIONS: This case report demonstrates the importance of monitoring patients carefully after the discontinuation of fingolimod for PML-IRIS and rebound MS with IRIS as these conditions may manifest similarly.