What is the most characteristic clinical sign of a left cerebral vascular accident (CVA)?

Aphasia is the most characteristic clinical sign of a left cerebral vascular accident (CVA) due to the fact that the left hemisphere of the brain is predominantly responsible for language processing in most individuals, particularly right-handed ones. A left CVA can disrupt the areas associated with speech and language, such as Broca's and Wernicke's areas, leading to difficulty in speaking, understanding, reading, or writing—conditions collectively referred to as aphasia.

While hemiparesis, ataxia, and dysarthria can also occur following a left CVA, they are not as uniquely indicative of left hemisphere damage as aphasia. Hemiparesis refers to weakness on one side of the body and is a common outcome of strokes regardless of the site of injury. Ataxia involves a lack of voluntary coordination of muscle movements and can arise from various neurological conditions. Dysarthria is characterized by difficulties in articulation and is often seen in conjunction with other neurological impairments, but it does not fully encapsulate the language deficits denoted by aphasia.

Thus, aphasia serves as a hallmark sign of left hemisphere involvement in a stroke, highlighting the role of that hemisphere in language function.