Clinical Reasoning: New-Onset Diplopia and Headache in a Patient with Metastatic Breast Cancer

A 54-year-old woman presented with progressively worsening headache and diplopia. Five months earlier, she began to experience imbalance and nonspecific dizziness, followed by intermittent tingling and numbness over her right eyebrow, eyelid, and cheekbone. For the next 2 months, she suffered intermittent severe right frontal headaches, subsequently transforming to an unremitting dull bifrontal headache without classical migrainous features or positional exacerbation. She then noticed horizontal binocular diplopia with a mild vertical component. She was referred to neurology by her oncologist.