Which statement is true about the differences between apraxia of speech and dysarthria?

• A. AOS errors increase with length and complexity of utterances, whereas dysarthric errors remain fairly constant.
• B. AOS always involves deficits in muscle ROM and tone, while dysarthria does not.
• C. AOS affects all five speech domains, whereas dysarthria affects only articulation.
• D. AOS never coexists with aphasia, whereas dysarthria always coexists with aphasia.

Answer: (A)

Understanding the difference here hinges on planning versus execution. Apraxia of speech is a motor planning problem: the brain struggles with sequencing the movements needed for speech. As utterances get longer or more complex, the planning demands grow, so errors become more frequent and groping or inconsistent sound substitutions appear, especially with longer sequences. Dysarthria, on the other hand, is a neuromuscular execution problem—weakness, reduced range of motion, or poor coordination of the articulators. Because the difficulty is in muscle execution rather than planning, the articulation errors tend to be more steady across utterance length and complexity.

That’s why the statement about errors increasing with length in AOS while dysarthric errors stay relatively constant best captures the key distinction. The other choices don’t fit as well: muscle ROM and tone deficits are a feature of dysarthria, not AOS; AOS can occur with aphasia and dysarthria is not required to co-occur with aphasia; and both disorders can affect more than just articulation, not neatly narrowing to one domain for one condition.