Sensomotor aphasia

An acquired speech disorder in which there is a disruption or loss of the ability to perceive, understand, and use speech as a means of communication is defined in clinical neurology as receptive-expressive or sensorimotor aphasia. [ 1 ], [ 2 ]

Epidemiology

According to clinical statistics, almost a third of cases of sensorimotor aphasia are associated with cerebrovascular accidents.

Previous research findings indicate that the incidence of aphasia is high. For example, in the United States, there are 180,000 cases of aphasia each year. Another study found that approximately 100,000 stroke survivors are diagnosed with aphasia each year. A study found that 15% of individuals under the age of 65 have aphasia after their first ischemic stroke. [ 3 ] The data also shows that this percentage increases to 43% for individuals aged 85 and above. [ 4 ]

According to the National Aphasia Association, 24-38% of people who have had a stroke suffer from total aphasia. And in 10-15% of cases, motor (expressive) aphasia or another type – sensory (or receptive) aphasia – occurs.

Causes sensorimotor aphasia

This type of speech disorder combines sensory (receptive) aphasia and motor (expressive). Thus, this is complete or total aphasia - a serious disorder of higher speech functions, the causes of which are associated with damage to two speech (language) areas of the cortex of the dominant (in right-handed people - the left) hemisphere of the brain.

Firstly, this is the Broca's area, located in the inferior gyrus of the temporal lobe, which, interacting with the flow of sensory information from the temporal cortex, participates in its processing (phonological, semantic and syntactic) and synchronization, selects the necessary algorithm (phonetic code) and transmits it to the motor cortex that controls articulation. [ 5 ]

Secondly, it is the Wernicke area, which is connected to Broca's area by a bundle of nerve fibers and is located in the posterior part of the superior temporal gyrus and is responsible for speech perception (segmentation into phonemes, syllables, words) and its understanding (definition of the semantics of words and integration of phrases in context). [ 6 ]

In addition, adjacent frontotemporal cortex areas (inferior frontal gyrus, superior and middle temporal gyrus) and subcortical areas associated with the speech perception network by the thalamic neuronal nuclei; basal ganglia and angular gyrus of the posterior parietal lobe; primary motor and dorsal premotor cortex; areas of the insular cortex, etc., may be damaged.

Most often, sensorimotor aphasia develops after a stroke, in particular, ischemic (cerebral infarction), in which the blood supply to these areas of the brain is disrupted due to the blockage of a cerebral blood vessel by a thrombus. Experts consider post-stroke complete aphasia not only an important marker of the severity of the condition, but also an indicator of an increased risk of death and the likelihood of developing cognitive impairment in the form of vascular dementia.

Read - Criteria for assessing cognitive impairment after stroke

There are such types of total aphasia as transient (temporary) and permanent (constant). So, transient global aphasia can be caused by transient ischemic attacks (temporary disturbances of cerebral circulation that do not lead to irreversible damage to the brain) - microstrokes, as well as severe attacks of aphasic migraine or epileptic seizures.

Receptive-expressive aphasia may result from traumatic brain injury, brain infections (encephalitis), intracerebral or subarachnoid hemorrhage, cerebral tumors, neurodegenerative diseases such as frontotemporal or frontotemporal dementia (with the development of profound permanent speech disorder).

All of the listed conditions, as well as the presence of cerebrovascular diseases of various etiologies, are, in fact, risk factors for the development of global sensorimotor aphasia. [ 7 ]

Pathogenesis

Today, there are many uncertainties in understanding the mechanism of specific brain damage, but experts explain the development of sensorimotor aphasia by the alteration of not only the cerebral speech areas (Broca and Wernicke) - with the appearance of areas of cortical atrophy, but also by damage to the main axonal pathways, which leads to disruptions in such a complex CNS process as sensorimotor integration.

In the case of a brain tumor, its enlargement leads to damage to the cells of the speech zones and their dysfunction.

And in cases of ischemic stroke in the area of blood supply of the superficial branches of the middle cerebral artery (arteria cerebri media), which supply blood to Broca's and Wernicke's areas, the mechanism of speech disorder is associated with a lack of oxygen and deterioration of the trophism of these cerebral structures and part of the lateral cortex of the brain. [ 8 ]

Symptoms sensorimotor aphasia

Depending on factors such as the size of the lesion and its location, the symptoms of sensorimotor aphasia may vary from patient to patient. But the first signs are manifested by a significant limitation not only of the ability to speak (speech praxis), but also problems with understanding language.

Speech in sensorimotor aphasia may be almost completely absent: patients are able to pronounce sounds and several separate words or an incomprehensible set of parts of words (with grammatical errors); do not understand oral speech; cannot repeat what others have said and give an answer (“yes” or “no”) to elementary questions.

Attempts at non-verbal communication using gestures and facial expressions are often observed.

Emotional arousal in sensorimotor aphasia indicates that the damage has affected the structures of the limbic system of the brain (the frontotemporal cortex or part of the temporal lobe cortex - the entorhinal cortex, hippocampus or cingulate gyrus), or the patient has developed the third stage of cerebrovascular insufficiency caused by chronic cerebral circulatory failure. [ 9 ]

Complications and consequences

Total aphasia is the most severe form of aphasia, and as a result of damage to the speech areas of the brain, the consequences and complications affect all aspects of speech and communication, and in dementia, cognitive abilities. [ 10 ]

Sensorimotor aphasia can lead to:

• secondary (aphasic) mutism (complete silence );
• inability to name objects - anomie;
• loss of writing skills - agraphia;
• loss of reading skills - alexia.

Diagnostics sensorimotor aphasia

Diagnosis of aphasia, as well as determination of its type, is carried out on the basis of clinical symptoms using a study of the neuropsychic sphere of patients and speech testing.

Instrumental diagnostics includes:

• computed tomography of the brain;
• magnetic resonance imaging (MRI) of the brain;
• electroencephalography (which studies the bioelectrical activity of the brain);
• Doppler sonography of cerebral vessels.

Differential diagnosis

Differential diagnosis should be made with other speech disorders, including Broca's or Wernicke's aphasia, dysarthria, anarthria, apraxia (oral type) and apraxic dysarthria, as well as Alzheimer's disease.

Treatment sensorimotor aphasia

Treatment of receptive-expressive aphasia consists of reducing speech deficits during speech therapy sessions, as well as preserving the patient's remaining language skills. In addition, the most important goal of therapy is to teach the patient to communicate in alternative ways (gestures, images, using electronic devices).

More information in the article - Aphasia: causes, symptoms, diagnosis, treatment

For information on rehabilitation after a stroke, see the publication – Post-Stroke Condition

Along with speech therapy, in some cases transcranial brain stimulation is practiced – magnetic or direct current. [ 11 ], [ 12 ]

Melodic intonation therapy (MIT) uses melody and rhythm to improve a patient's speech fluency. The theory behind MIT is to use the intact non-dominant hemisphere, which is responsible for intonation, and reduce the use of the dominant hemisphere. MIT can only be used in patients with intact auditory perception. [ 13 ]

Prevention

It is still unknown how to prevent damage to the speech areas of the cerebral cortex in traumatic brain injury, stroke and other conditions etiologically associated with this speech disorder.

Forecast

The prognosis for the outcome and recovery of speech in sensorimotor aphasia depends on the severity of the brain damage and the person's age. [ 14 ] It is rare to be able to fully restore language abilities: two years after their loss as a result of a stroke, a satisfactory level of communication is observed in only 30-35% of patients.

However, over time, aphasia symptoms may improve, with language comprehension usually recovering more quickly than other language skills.