PRAXIS Motor Speech/Apraxia/Dysarthria

stroke, tumor, degenerative disease, or traumatic brain injury (TBI),

speech disorders that result from neurologic impairments affecting the motor planning, programming, neuromuscular control, or execution of speech. These impairments can lead to difficulties in producing speech sounds accurately and fluently.

There are two main types of motor speech disorders: Apraxia of Speech (AOS) and Dysarthria. AOS is characterized by difficulties in the motor planning or programming of sequential movements required for speech production. Dysarthria, on the other hand, is characterized by disturbances in speech muscle control due to factors like paralysis, weakness, slowness, incoordination, and altered muscle tone.

other parts of the body. For example, individuals with uncoordinated speech may also exhibit uncoordinated body movements, suggesting a broader impact of motor impairments on various motor functions in the body.

aphasia

language-dominant hemisphere, particularly in regions like Broca's area and the anterior insular cortex. Additionally, subcortical lesions involving the basal ganglia or regions of the parietal lobe may also be implicated in AOS.

language formulation and motor execution. It involves transforming abstract phonemes into a neural code compatible with the motor system to connect inner language processes with speech utterances.

concentrated effort in sequentially and volitionally producing phonemes for intelligible speech. Their speech may consist of "islands" of fluent and intelligible speech interrupted by periods of effortful groping for speech sounds. Automatic phrases may be produced fluently, but repeating the same utterance may be difficult.

AOS results in articulatory disturbances such as inconsistent trial and error responding, increased difficulty with longer and more complex utterances, and frequent speech sound substitutions. Prosodic disturbances include slow speech rate, hesitations, and difficulty initiating speech, known as articulatory groping.

flaccid, spastic, ataxic, hypokinetic, hyperkinetic, and mixed, with a seventh type called unilateral upper motor neuron (UUMN) dysarthria.

the site of lesion rather than the etiology of the lesion. Different conditions, such as a brainstem stroke, ALS, or an acoustic neuroma, can result in the same type of dysarthria.

Dysarthria reflects impairment in the ability to execute motor movements for speech production and often affects all speech processes (respiration, phonation, resonation, articulation, and prosody). In contrast, apraxia of speech primarily impacts articulation and prosody.

UUMN dysarthria results from lesions to the upper motor neurons and is the mildest form of dysarthria. It is characterized by contralateral lower facial weakness and tongue weakness, leading to primarily impacted articulation. Individuals with UUMN dysarthria may also present with aphasia and/or apraxia of speech.

Spastic dysarthria is a type of dysarthria that results from bilateral lesions to the upper motor neurons (UMNs). These lesions lead to significant dysarthria and are also referred to as pseudobulbar palsy because the lesion occurs above the level of the brainstem in the bulbar region.

The bilateral lesions result in a lack of inhibitory neural information reaching the cell bodies that give rise to the lower motor neurons (LMNs) in the brainstem and spinal cord. This leads to muscle weakness, hypertonia (too much muscle tone) with limited range of movement, and exaggerated reflexes.

The most common causes of spastic dysarthria are bilateral strokes or traumatic brain injuries (TBI), but other etiologies, such as degenerative diseases, can also account for some cases.

Flaccid dysarthria results from lesions affecting the lower motor neurons (LMNs), which include motor neuron cell bodies, peripheral nerves, neuromuscular junctions, and muscle fibers. Lesions can occur anywhere along the LMN and result in decreased muscle tone (hypotonia), muscle weakness, and muscle atrophy. Etiologies of flaccid dysarthria include brainstem stroke, traumatic brain injuries, ALS, myasthenia gravis, and muscular dystrophies.

The extent and severity of speech systems affected by flaccid dysarthria depend on the site of the lesion. If the lesion occurs peripherally, closer to the innervation of the targeted muscle, symptoms will be specific to that system. On the other hand, if the lesion occurs higher up, near the brainstem, multiple cranial nerves may be affected, leading to more pervasive and severe symptoms.

Ataxic dysarthria results from damage to the cerebellum and its associated tracts. Causes of lesions can include degenerative diseases, stroke, traumatic brain injuries, and tumors. The cerebellum is responsible for coordinating movement, and damage to it leads to uncoordinated movements and lack of synergy. Ataxic dysarthria affects all speech systems, particularly impacting the prosodic features of speech.

Hypokinetic dysarthria is caused by damage to the basal ganglia system, specifically involving the substantia nigra. It is associated with Parkinson's disease (PD) and is characterized by decreased movement (bradykinesia), muscle rigidity, resting tremor, and difficulty initiating movement. Individuals with PD may also present with stooped posture, masked facies (decreased facial expression), and a festinating gait. Most speech processes are affected in hypokinetic dysarthria, with notable symptoms in phonation and articulation.

Hyperkinetic dysarthria is classified into two types based on the speed of involuntary movements. Slow hyperkinetic dysarthria, such as with dystonia, is characterized by slow, writhing movements that slowly build to a peak and are sustained before subsiding. Quick hyperkinetic dysarthria, associated with chorea, involves fast, brief, and unpredictable movements. These dysarthrias are caused by pathologies affecting the basal ganglia and associated circuitry in the cerebral hemispheres, including conditions like congenital cerebral palsy of the athetoid type (resulting in dystonia) and degenerative Huntington's disease (resulting in chorea).

Mixed dysarthrias result from a combination of two or more of the previously mentioned dysarthria types. They often occur in degenerative disorders like amyotrophic lateral sclerosis (ALS) or multiple sclerosis (MS) or when trauma affects multiple areas of the nervous system, such as traumatic brain injury (TBI) or multiple strokes. The speech systems affected in mixed dysarthrias vary depending on the combination of dysarthria types.

Swallowing impairments are referred to as dysphagia, which can be a co-occurring condition with motor speech disorders, especially dysarthria, due to the impact of associated pathology on the motor system and the muscles involved in swallowing. Acquired neurologic disorders, including stroke, TBI, tumors, and degenerative diseases, can lead to neurogenic dysphagia. Unlike dysarthrias, there is no clear correlation between the lesion site and expected symptoms for neurogenic dysphagia.