What is a key symptom of the lateral medullary syndrome?

The key symptom of lateral medullary syndrome, also known as Wallenberg's syndrome, is the loss of pain and temperature sensation. This occurs due to the infarction of the lateral part of the medulla oblongata, which affects the spinothalamic tract and the nucleus of the trigeminal nerve. The spinothalamic tract transmits pain and temperature sensations from the contralateral side of the body, while the nucleus of the trigeminal nerve is responsible for conveying these sensations from the ipsilateral face. Consequently, patients typically present with a contralateral loss of pain and temperature sensation in the body and an ipsilateral loss in the face.

Facial pain can occur in various neurological conditions but is not a hallmark symptom of this specific syndrome. Contralateral hemiplegia is more characteristic of other brainstem strokes affecting different areas, particularly involving the corticospinal tract. Respiratory distress is associated with severe brainstem strokes that impact vital functions but is not specifically indicative of lateral medullary syndrome itself. Therefore, the hallmark loss of pain and temperature sensation is what distinguishes this condition and confirms the choice provided.