19th February 2024

A 74-year-old male presents to the acute medical unit with ptosis.

A 74-year-old male presents to the acute medical unit with ptosis. He is noted to have a left-sided ptosis and an associated diplopia towards the left. He also notes that he is persistently dizzy despite sitting and cannot walk without leaning towards the left. He is noted to have anisocoria with miosis affecting his left eye. Despite the heat, the patient notes that he is also unable to sweat on the left side of his face and upper body. 

Given the clinical findings, what is the likely cause for the patient’s Horner’s syndrome?