Motor Speech Disorders: Dysarthria and Apraxia

Motor Speech Disorders: Dysarthria and Apraxia

What are motor speech disorders?

Speech is a complex sensory and motor process that develops through the use of hearing, voice, and the oral–facial system, requiring rapid coordination of multiple physiological systems and neural integration. Motor speech disorders are communication disorders that arise when a neuro-motor problem affects one or more components of speech, including respiration, phonation (voice production), resonance, articulation, and prosody. There are two main types of motor speech disorders: dysarthria and apraxia.

What is Dysarthria?

Dysarthria is a motor speech disorder resulting from damage to the Central Nervous System (CNS), the Peripheral Nervous System (PNS), or both. This damage causes impairment in the muscles responsible for speech production, leading to spasticity, flaccidity, incoordination, or paralysis. As a result, speech components such as respiration, phonation, resonance, articulation, and prosody are affected, and speech intelligibility is reduced.

In which conditions is dysarthria seen?

Dysarthria may result from vascular, traumatic, infectious, neoplastic, or metabolic causes. Different lesions in the central or peripheral nervous system lead to different types of dysarthria. The term is often used for acquired neurological speech disorders in adults, such as those caused by stroke or brain injury. In childhood, it is commonly associated with cerebral palsy and is referred to as “developmental dysarthria.”

Conditions associated with dysarthria include:

• Cerebrovascular accidents (stroke)
• Traumatic brain injury
• Tumors
• Cerebral palsy
• Progressive supranuclear palsy
• Parkinson’s disease
• Huntington’s disease
• Amyotrophic lateral sclerosis (ALS)
• Multiple sclerosis
• Myasthenia gravis

Types of Dysarthria

1. Spastic Dysarthria

Caused by upper motor neuron lesions. It is characterized by a strained and harsh voice, low pitch range, hypernasality, imprecise consonants, reduced stress, and slow speech.

2. Flaccid Dysarthria

Caused by lower motor neuron lesions or cranial nerve damage. It includes weak breath support, breathy voice, hypernasality, nasal air emission, and imprecise articulation.

3. Ataxic Dysarthria

Caused by cerebellar damage. It is characterized by irregular speech rhythm, excess and equal stress, scanning speech, distorted vowels, and poor coordination.

4. Hypokinetic Dysarthria

Seen in basal ganglia disorders such as Parkinson’s disease. Features include reduced loudness, monotone speech, short phrases, and tremor.

5. Hyperkinetic Dysarthria

Associated with basal ganglia dysfunction. It involves involuntary movements affecting speech, irregular pitch and loudness, and disrupted speech flow.

6. Mixed Dysarthria (Spastic-Flaccid)

Seen in conditions like ALS, involving both upper and lower motor neuron damage, leading to combined symptoms.

7. Mixed Dysarthria (Spastic-Ataxic)

Seen in multiple sclerosis, involving both upper motor neuron and cerebellar dysfunction.

Dysarthria Assessment

The purpose of assessment is screening, diagnosis, and intervention planning. It includes imaging techniques, direct observation of speech-related structures, and perceptual evaluation of speech. Acoustic analysis tools (e.g., computerized speech systems), audio, and video recordings are used for objective evaluation.

Goals of Dysarthria Therapy

The main goal is to maximize the individual’s communication abilities by improving speech intelligibility, rate, duration, naturalness, prosody, and participation in daily communication activities.

When is AAC (Augmentative and Alternative Communication) needed?

AAC may be used temporarily in acute non-progressive cases or long-term in chronic conditions. In progressive disorders, it may start as a support and eventually become the primary communication method.

APRAXIA

What is Apraxia?

Apraxia is the inability to perform skilled or learned movements despite having normal strength, coordination, sensation, and comprehension. It is a form of motor agnosia.

Types of Apraxia

• Motor Apraxia: Disruption of learned movement patterns
• Limb-Kinetic Apraxia: Loss of fine, precise movement
• Ideomotor Apraxia: Difficulty performing movements on command
• Ideational Apraxia: Impairment in planning complex sequences of actions
• Gait Apraxia: Difficulty initiating or controlling walking
• Speech Apraxia (Verbal Apraxia): Impairment in motor planning for speech

What is Speech Apraxia?

Speech apraxia is a motor planning disorder affecting speech production. It occurs in both adults and children. It involves difficulty in programming the movements required for speech despite intact muscle function.

Characteristics of Apraxic Speech

• Inconsistent speech errors
• Difficulty increasing word length
• Distortions and repetitions
• Greater difficulty with consonants than vowels
• Better production of automatic speech
• Awareness of speech errors

Goals of Apraxia Therapy

The main goal is to improve voluntary control of speech motor planning. In severe cases, alternative communication systems may be more appropriate than focusing solely on speech improvement.