A twelve-year-old, previously healthy, right-handed girl presented to theemergency department with sudden onset right arm weakness, aphasia and
confusion. Altered mentation, expressive aphasia and right hemiparesis were
noted.She underwent emergent MRI brain for concerns of acute stroke, which ruled out the same. Continuous EEG monitoring showed marked left hemispheric slowing but no focal seizures. For suspicion of complex hemiplegic migraine, she received a combination of ketorolac, diphenhydramine and prochlorperazine. This led to resolution of weakness and aphasia, along with return to baseline mentation. However, left hemispheric slowing persisted on EEG even at the time of discharge. Two weeks later, a repeat routine EEG showed continued slowing in the left occipital region, while patient clinically continued to function at baseline and had not had any further episodes. Four weeks after the original event, EEG returned to symmetric brain activity with no other abnormalities. Subsequently, family shared that patient's mother and maternal aunt experience symptoms consistent with hem legic migraines, but had never been formally diagnosed. With this crucial information, we proceeded with genetic testing which revealed a mutation in the ATP1A2 gene, establishing the diagnosis as Familial Hemiplegic Migraine (FHM).