Doctor, I'm Seeing Two of Everything.

Acute diplopia is a rare chief complaint with a broad differential diagnosis; key historical and physical characteristics aid with emergency management. This case report discusses the important findings, imaging, and multidisciplinary interaction between emergency medicine, ophthalmology, and neurology regarding the approach to addressing acute painless vertical diplopia. A 51-year-old male presented to the emergency department (ED), reporting that he was seeing 'two of everything,' since awakening. Although the patient had a history of ischemic stroke, he had never experienced this sensation of diplopia. His ED workup was essentially unremarkable; he was admitted for evaluation of the possibilities of a fourth cranial nerve (CN IV) palsy, acute Parinaud syndrome, or ischemic stroke. Ultimately the patient was sent home one day after admission with the diagnosis of CN IV neuropathy. Highlighted is an approach to undifferentiated diplopia with an included discussion of the pathophysiology of a CN IV palsy and Parinaud syndrome. Understanding basic pathophysiology and anatomy allows for a proper history, physical exam, and appropriate consultation. With these tools, emergency physicians can improve their approach to patients with acute diplopia when arriving at the ED.