Alemtuzumab, approved for relapsing-remitting multiple sclerosis (RRMS), carries life-threatening adverse events including stroke and cervicocephalic arterial dissections. Here we report a case of a patient who developed an intraparenchymal hemorrhage (IPH) related to multiple intracranial pseudoaneurysms and cervical arterial dissection immediately following alemtuzumab infusion.

A 27-year-old woman with a history of RRMS presented with a headache immediately following infusion of alemtuzumab. Magnetic resonance imaging (MRI) of the brain revealed a right-sided basal ganglia hemorrhage and hydrocephalus. Computed tomography angiogram of the head and neck demonstrated multi-vessel dilatations resembling pseudoaneurysms involving the carotid and the vertebrobasilar system. Central nervous system (CNS) vasculitis was suspected and the patient was started on steroids.  Extensive rheumatologic workup was unremarkable.  Repeat imaging demonstrated persistent dilatation of the intracerebral large vessels and dissection of the vertebral and carotid arteries. The patient was diagnosed with alemtuzumab-induced arterial dissection and subsequent IPH. Alemtuzumab and steroids were discontinued with complete resolution of symptoms. 

Alemtuzumab is a monoclonal antibody approved for the treatment of RRMS. Due to its long-term efficacy, repeated infusions are not warranted.  The clinical benefit of this agent is limited by its frequent side effects. In 2018, the FDA investigated 13 cases of stroke and cervical arterial dissections associated with the use of alemtuzumab. In 12 of the 13 cases, the event occurred within 24 hours of infusion completion, prompting the release of a black box warning.  Cerebrovascular complications following the use of alemtuzumab are rare, and alternative etiologies such as primary angitis of the CNS are typically considered.

IPH and multifocal dissecting pseudoaneurysms are rare complications associated with the use of alemtuzumab.  We advise clinicians to be aware of this potentially life-threatening condition in patients with RRMS treated with this agent.