Focal lesions of the area postrema are a rarely reported cause of cyclical vomiting and present a diagnostic challenge to both clinician and radiologist. While cannabinoids have been shown to bind central CB1/2 receptors and reduce chemotherapy-associated emesis, their role in other vomiting disorders is less established.

A 30-year-old female presented to the neurology clinic with a 15-year history of cyclical vomiting. She experienced 20 symptomatic days a month, during which she would vomit up to 8 times over a period of 5-6 hours. Nasal sumatriptan provided only minimal relief, and she was frequently hospitalized during these episodes for intravenous hydration. An extensive workup at multiple institutions failed to identify a cause for her vomiting. The neurological exam was unremarkable. 

An MRI of the brain was ordered to assess intracranial pathology. The MRI was initially read as normal; however, on review, a small central hypointensity at the caudal end of the fourth ventricle consistent with a focal lesion of the area postrema was noted. A repeat MRI four months later confirmed the finding.

Given a presumed central etiology for the vomiting and the limited success of conventional therapy, a trial of medical marijuana was recommended. The patient was prescribed 10mg of 1:1 CBD:THC daily with 30mg CBD to be taken at the onset of vomiting episodes. On this regimen, the frequency of episodes was reduced to 7 times a month and the duration was reduced to 3-5 hours. There were no further hospitalizations, and the patient reported significant improvement in quality of life.

 This case of a rare focal lesion of the area postrema highlights the importance of investigating central neurological causes in patients with persistent unexplained vomiting, even in the presence of a normal neurological exam, and the utility of marijuana in managing this broad spectrum of disease.