Motor Speech Disorders

Motor speech disorders are a collection of communi­cation disorders involving retrieval and activation of motor plans for speech, or the execution of movements for speech production (7).

Acquired: adverse event (usually neurologic) occurs that impedes continuation of previously normal speech acquisition

Developmental: no specific identifiable etiology to explain delays in speech acquisition

Dysarthria refers to a group of related motor speech disorders resulting from impaired muscular control of the speech mechanism, and manifested as disrupted or distorted oral communication due to paralysis, weakness, abnormal tone, or incoordination of the muscles used in speech (Table 4.4) (8). It affects the following:

4.3

Motor Speech Disorders

Respiration: respiratory support for speech, breathing/ speaking synchrony, sustained phonation

Phonation/Voice: loudness, quality

Articulation: precision of consonants and vowels Resonance: degree of airflow through nasal cavity Prosody: melody of speech, use of stress and inflection

Movements may be impaired in force, timing, endurance, direction, and range of motion. Sites of lesion include bilateral cortices, cranial nerves, spinal nerves, basal ganglia and cerebellum.

Associated characteristics of dysarthrias include slurred speech; imprecise articulatory contacts; weak respiratory support and low volume; incoordination of the respiratory stream; hypernasality; harsh or strained/strangled vocal quality; weak, hypophonic, breathy vocal quality; involuntary movements of the oral facial muscles; spasticity or flaccidity of the oral facial muscles; and hypokinetic speech.

Some common etiologies for dysarthria in chil­dren include stroke, brain tumor, aneurysm, traumatic brain injury, encephalopathy, seizure disorder, cere­bral palsy, and high-level spinal cord injury.

Oral apraxia refers to an impairment of the vol­untary ability to produce movements of the facial, labial, mandibular, lingual, palatal, pharyngeal, or laryngeal musculature in the absence of muscle weakness.

Verbal apraxia (also called apraxia of speech, or AOS) refers to an impairment of motor speech charac­terized by a diminished ability to program the posi­tioning and sequencing of movements of the speech musculature for volitional production of speech sounds. Apraxia is not the result of muscle paralysis or weakness, but may lead to perceptual disturbances of breathing/speaking synchrony, articulation, and pros­ody. Site of lesion is generally the left precentral motor or insular areas.

Developmental verbal apraxia (also called develop­mental apraxia of speech, or DAOS) refers to a speech disorder resulting from delays or deviances in those processes involved in planning and programming movement sequences for speech in the absence of mus­cle weakness or paralysis. Associated characteristics of DAOS include receptive-better-than-expressive lan­guage, presence of oral apraxia (may or may not exist with DAOS), phonemic errors (often sound omissions), difficulty achieving initial articulatory configuration, increase in errors with increase in word length and/ or phonetic complexity, connected speech poorer than word production, inconsistent error patterns, groping and/or trial-and-error behavior, and presence of vowel errors.

4.4

Types of Dysarthria

Source: From Ref. 8.

Children with motor speech disorders may dem­onstrate impaired phonological systems because their ability to acquire the sound system of their language is believed to be undermined by difficulties in managing the intense motor demands of connected speech (9).