Today’s USMLE® Step 1 question of the day focuses on identifying the vascular structure most likely affected in an elderly patient with acute neurological deficits. What’s the answer? Let’s find out!
An 85-year-old man is brought to the emergency room after being found on the floor in his home. Past medical history is significant for hypertension and hyperlipidemia. Temperature is 37.7°C (99.8°F), pulse is 101/min, respirations are 22/min, and blood pressure is 188/94 mmHg. The patient appears conscious, but does not demonstrate spontaneous movement of the extremities and is unable to respond to voice or painful stimuli. The patient is able to blink and eye movements are restricted to the vertical plane.
Magnetic resonance angiogram will most likely reveal ischemia of which of the following vascular structures?
A. Posterior inferior cerebellar artery
B. Anterior spinal artery
C. Anterior inferior cerebellar artery
D. Basilar artery
E. Posterior cerebral artery
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
D. Basilar artery
Correct: See Main Explanation.
Incorrect Answer Explanations
A. Posterior inferior cerebellar artery
Incorrect: Posterior inferior cerebellar artery occlusion results in lateral medullary (Wallenberg) syndrome characterized by vertigo/nystagmus, ipsilateral cerebellar signs, loss of pain/temperature sensation on the ipsilateral face and contralateral body, bulbar weakness, and Horner syndrome.
B. Anterior spinal artery
Incorrect: Infarction of the paramedian branches of anterior spinal artery results in medial medullary syndrome, which typically presents with contralateral hemiparesis (lateral corticospinal tract), decreased contralateral proprioception (medial lemniscus), and ipsilateral tongue paralysis (hypoglossal nucleus).
C. Anterior inferior cerebellar artery
Incorrect: Lateral pontine syndrome occurs secondary to occlusion of anterior inferior cerebellar artery (AICA). Patients typically present with signs of a lower motor neuron facial nerve lesion, vertigo/nystagmus, ipsilateral cerebellar signs, loss of pain/temperature sensation on the ipsilateral face and contralateral body, ipsilateral sensorineural loss, and Horner syndrome.
E. Posterior cerebral artery
Incorrect: Posterior cerebral artery infarction typically results in contralateral hemianopia due to infarction of the visual cortex. The macula is often spared due to contralateral circulation from the middle cerebral artery.
Main Explanation
This patient’s inability to move the extremities, loss of horizontal eye movements with preserved consciousness, and loss of mouth, tongue, and facial movements, is consistent with locked-in syndrome (LIS), due to the occlusion of the basilar artery. The most vulnerable territory associated with this condition lies at the paramedian base of the pons.
Clinical features consistent with locked-in syndrome include:
- Quadriplegia and inability to speak or swallow due to the involvement of corticospinal and corticobulbar tracts
- Preserved consciousness due to the sparing of the reticular formation
- Loss of horizontal eye movement due to the involvement of ocular cranial nerve nuclei and paramedian pontine reticular formation
- Voluntary blinking and vertical eye movements remain intact, which are controlled in the rostral portion of the brainstem
Major Takeaway
Locked-in syndrome (LIS) is characterized by quadriplegia and inability to speak or swallow with retained consciousness. Patients with this condition often retain the ability to blink and vertical eye movements.
Want to learn more about this topic?
Read this Osmosis high-yield note: Anatomy clinical correlates: Posterior blood supply to the brain
References
- Bruno, M. A., Schnakers, C., Damas, F., Pellas, F., Lutte, I., Bernheim, J., … & Laureys, S. (2009). Locked-in syndrome in children: report of five cases and review of the literature. Pediatric neurology, 41(4), 237-246.
- Fix, J., & Brueckner, J. (2009). High-yield neuroanatomy (4th ed.). Philadelphia, Pa.: Wolters Kluwer, Lippincott, Williams et Wilkins.
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