Final Answer:
The most likely cause of a new seizure in a patient over 65 years old would be cerebrovascular disease, such as a stroke.
Step-by-step explanation:
In individuals over the age of 65, cerebrovascular disease becomes a prominent risk factor for new-onset seizures. Conditions like ischemic or hemorrhagic strokes, which affect blood flow to the brain, can trigger seizures due to the disruption of normal neural activity. Other potential causes in this age group may include brain tumors, neurodegenerative disorders, or metabolic imbalances. However, the prevalence of cerebrovascular disease makes it a primary consideration when evaluating a new seizure in elderly patients.