A 63-year-old man presents to the emergency department because of transient symptoms of vertigo, slurred speech, diplopia, and paresthesia. He is symptom-free now, and clinical examination is entirely normal. His past medical history is significant for osteoarthritis, hypertension, and dyslipidemia. Which of the following is the most likely cause for symptoms?

**Core Concept**
The patient's transient symptoms of vertigo, slurred speech, diplopia, and paresthesia suggest a cerebral embolic event, which is a blockage of a blood vessel in the brain. This is often caused by a blood clot or other debris that travels through the bloodstream and lodges in a cerebral artery.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with a transient ischemic attack (TIA), also known as a "mini-stroke." TIAs occur when a blood clot temporarily blocks a cerebral artery, causing symptoms that resolve once the blood flow is restored. The patient's risk factors for atherosclerosis, including hypertension, dyslipidemia, and osteoarthritis, increase his likelihood of having a TIA.

**Option A:** Atrial septal defect (ASD) is a congenital heart defect that allows blood to flow between the left and right atria. While it can increase the risk of embolic events, it is not the most likely cause of this patient's symptoms, which are more consistent with a TIA.

**Option B:** Mitral valve prolapse is a condition in which the mitral valve does not close properly, allowing blood to flow backward into the left atrium. It is not a common cause of embolic events, and the patient's symptoms suggest a more acute process.

**Option C:** This option is missing.

**Option D:** This option is missing.

**Clinical Pearl / High-Yield Fact**
TIA symptoms often resolve within 24 hours, but up to one-quarter of patients experience a full-blown stroke within 90 days. Therefore, it is essential to investigate and manage the underlying causes of TIA to prevent future ischemic events.

**Correct Answer:** C.

✓ Correct Answer: A. posterior circulation transient ischemic attack (TIA)