Multiple sclerosis (MS) is a chronic neurologic disorder effecting approximately 2.5 million people worldwide. With improved neuroimaging and earlier diagnosis, the use of disease-modifying therapies (DMT) is increasing. Understanding both common and rare side effects of DMTs is critical for delivering appropriate clinical care. We present a case of fingolimod-induced posterior reversible encephalopathy syndrome (PRES).

Fingolimod is a sphingosine-1-phosphate receptor (S1P) modulator approved for relapsing-remitting MS. S1P receptors are found throughout the body including endothelial cells.  The presence of S1P is essential in maintaining the integrity of endothelium.

PRES causes changes in the endothelium of blood vessels via cytokine release, resulting in breakdown of the blood-brain barrier and vasogenic edema. This typically occurs in the posterior circulation of the intracerebral vasculature likely due to the lack of sympathetic innervation in these vessels. PRES is often associated with hypertensive crisis, renal disorders, and immunosuppressant use. There are a limited number of cases of PRES associated with fingolimod use in MS patients. Classically, PRES symptoms include headache, seizures, encephalopathy, and visual disturbances.

Our patient is a 48-year-old woman who had a witnessed generalized seizure and persistent encephalopathy.  Initial blood pressure was 207/110 and she required intubation for airway protection due to aspiration from the seizure and encephalopathy. MRI brain showed confluent T2 signal in bilateral parietooccipital/temporoparietal regions. With cessation of fingolimod and normalization of her BP, she remained seizure-free; her mental status and headache gradually improved. At four-month follow-up in clinic, she had continued improvement in her cognition, headache resolution and MRI brain showed significant decrease in the T2 signal previously seen and laminar necrosis in bilateral temporoparietal regions, typical finding seen with PRES.

Though a rare complication of fingolimod use, it’s important for clinicians to be aware of PRES due to its potential reversibility if identified early and treated effectively.