Which statement best distinguishes apraxia of speech (AOS) from dysarthria?

• A. AOS is a motor planning/programming disorder with inconsistent errors and groping, with preserved muscle strength; dysarthria reflects neuromuscular execution deficits with consistent errors across tasks.
• B. Dysarthria is a motor planning disorder with inconsistent errors.
• C. AOS primarily affects language comprehension.
• D. AOS is a purely cognitive disorder with no motor involvement.

Answer: (C)

Understanding the difference between apraxia of speech and dysarthria hinges on where the breakdown in speech happens—in planning the movements or in executing them. Apraxia of speech is a motor planning/programming problem: the brain has trouble planning the sequence of movements for speech, so articulatory patterns are inconsistent from attempt to attempt, and people often pause, search, and grope for the right sounds even though their muscles are not weak. The muscles themselves are typically strong, so strength isn’t the primary issue. Dysarthria, by contrast, reflects neuromuscular execution problems: weakness, slowness, or poor coordination of the speech muscles lead to more uniform, predictable errors across utterances and tasks, with slower rate and distorted speech as a result of the impaired execution. Language comprehension is generally preserved in AOS; the difficulty is in producing the speech, not understanding language. Therefore a statement that AOS is primarily about language comprehension doesn’t fit, while the key distinction lies in AOS’s planning/ programming nature with inconsistent errors and preserved strength versus dysarthria’s execution deficits.