Clinical Reasoning: Progressive Headache and Diplopia in an 89-Year-Old Man.

An 89-year-old man presented with a 3-year history of chronic daily headaches that significantly worsened over the past 4 months. Initially episodic, the left-sided headaches became continuous and were accompanied by systemic symptoms such as weight loss and elevated inflammatory markers, specifically C-reactive protein and erythrocyte sedimentation rate. Over subsequent weeks, the neurologic examination revealed new-onset left-sided ophthalmoplegia, ptosis, and marked visual acuity loss. This article explores the differential diagnosis for such a complex clinical presentation and highlights how a systematic diagnostic approach can guide clinicians toward the correct diagnosis.