Tumefactive demyelination and a malignant course in an MS patient during and following fingolimod therapy

• We report a severe side effect of fingolimod.
• Immuno-suppressive therapy in MS is associated with severe side effects.
• Diagnosis of space taking lesion in MS under therapy may require brain biopsy.

Finglimod, a sphingosine 1-phosphate receptor modulator, is the first orally administered therapy approved for prophylaxis in multiple sclerosis (MS). Several reports in the last two years suggested that it might be associated with severe augmentation of disease activity upon initiation or discontinuation of therapy. We present an MS patient who developed a giant cavitating brain lesion under fingolimod and in whom cessation of therapy was associated with a very active course. Brain biopsy revealed the lesion to be due to an active demyelinating inflammatory process. With the current wave of immunosuppressive treatments for MS, there is a need to be vigilant to side effects and risks not identified in large multicenter trials, collect the data and set guidelines and precautions for present and future medications.