Motor Speech Disorders: Dysarthria and Apraxia of Speech

Motor speech disorders are impairments of speech that arise from neurological damage to the systems that plan, program, and execute the movements of speech. The two principal types are dysarthria, a disturbance of the neuromuscular execution of speech, and apraxia of speech, a disturbance of the motor planning and programming of speech, each producing characteristic patterns of impaired articulation.

Definition

Motor speech disorders are speech impairments resulting from neurological dysfunction of the motor systems for speech: dysarthria reflects impaired strength, speed, range, steadiness, tone, or coordination of the speech musculature (execution), whereas apraxia of speech reflects impaired planning and programming of articulatory movements in the absence of weakness sufficient to explain the errors.

Scope

This topic covers the two main motor speech disorders — dysarthria and apraxia of speech — their conceptual separation from phonological and structural causes of imprecise speech, the perceptual approach to classifying dysarthria types, and the recognition of childhood apraxia of speech. It is reference material describing the disorder category and does not provide diagnostic or treatment instructions for any person.

Core questions

• How does dysarthria (execution) differ from apraxia of speech (planning and programming)?
• How are the perceptual subtypes of dysarthria related to the site of neurological lesion?
• What features distinguish childhood apraxia of speech from other pediatric speech sound disorders?
• How are motor speech disorders separated from phonological and structural causes of imprecise speech?

Key concepts

• Dysarthria versus apraxia of speech
• Perceptual classification of dysarthria types (for example, flaccid, spastic, ataxic, hypokinetic, hyperkinetic, mixed)
• Motor planning and programming versus neuromuscular execution
• Childhood apraxia of speech
• Speech subsystems (respiration, phonation, resonance, articulation, prosody)
• Inconsistent errors and prosodic disturbance

Mechanisms

Speech depends on a chain from motor planning and programming of articulatory targets to neuromuscular execution across the respiratory, laryngeal, velopharyngeal, and articulatory subsystems. In dysarthria, neurological damage impairs execution — altering strength, tone, speed, range, or coordination — and the resulting perceptual pattern reflects the affected motor system; Darley, Aronson, and Brown's classic Mayo Clinic work established that distinct dysarthria types can be differentiated perceptually and linked to lesion sites. In apraxia of speech, execution capacity is relatively spared but the planning and programming of movement sequences is disrupted, yielding effortful, inconsistent articulatory errors and disturbed prosody; childhood apraxia of speech is recognized as a pediatric motor speech disorder with this core deficit (ASHA, 2007).

Clinical relevance

Motor speech disorders are central to adult neurological rehabilitation (for example after stroke or in progressive neurological disease) and to pediatric speech-language pathology in the case of childhood apraxia of speech. Distinguishing a motor speech disorder from a phonological or structural one shapes how a case is understood. This entry describes the category for reference and is not a basis for individual diagnosis or management.

Epidemiology

Dysarthria is among the most common acquired communication disorders in adult neurology, occurring across many conditions including stroke and progressive neurological diseases; precise population frequencies depend on the underlying condition. Childhood apraxia of speech is considered relatively uncommon among pediatric speech sound disorders, but reliable population prevalence is limited by differing diagnostic criteria (ASHA, 2007).

History

The modern study of motor speech disorders was shaped by Darley, Aronson, and Brown's late-1960s Mayo Clinic studies, which introduced a perceptual method for differentiating dysarthria types and linking them to neurological substrates. The understanding of apraxia of speech as a disorder of motor planning distinct from dysarthria and from aphasia developed in parallel, and childhood apraxia of speech was consolidated as a recognized pediatric diagnosis in later expert reports such as the ASHA technical report of 2007.

Debates

How should childhood apraxia of speech be defined and diagnosed?

Because no single feature is pathognomonic, the diagnostic criteria and core markers for childhood apraxia of speech remain debated, complicating prevalence estimates and differentiation from severe phonological disorder.

Key figures

• Frederic Darley
• Arnold Aronson
• Joe Brown
• Joseph Duffy

Seminal works

• darley-1969
• asha-cas-2007

Frequently asked questions

What is the difference between dysarthria and apraxia of speech?

Dysarthria is a problem with the muscular execution of speech (weakness, slowness, or incoordination), whereas apraxia of speech is a problem with planning and programming the movements of speech, so the muscles are capable but the sequencing of articulation is disrupted.

Is childhood apraxia of speech the same as a phonological disorder?

No. Childhood apraxia of speech is a motor speech disorder affecting the planning of speech movements, with effortful and inconsistent errors and disturbed prosody, which distinguishes it from rule-based phonological disorders, although the two can be difficult to tell apart.