A 62-year-old man with a history of hypertension and tobacco use presents with sudden-onset dizziness and difficulty walking. Neurologic examination shows right-sided ptosis and miosis. He has decreased pain and temperature sensation on the right side of the face and on the left side of the body. Motor strength is full in all extremities. Which additional neurologic deficit is most likely to be present?

(Use the brainstem “Rules of 4” to localize the involved structure.)