Sensorimotor aphasia

Acquired speech disorder, in which there is a violation 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.

The results of previous studies indicate a high frequency of aphasia. For example, in the United States, 180,000 cases of aphasia are recorded annually. Another study found that approximately 100,000 stroke survivors are diagnosed with aphasia each year. The study showed that 15% of people under the age of 65 suffer from aphasia after the first ischemic stroke. [3]The data also shows that this percentage increases to 43% for those aged 85 and over.[4]

The US National Aphasia Association estimates that 24-38% of stroke survivors suffer from total aphasia. And in 10-15% of cases, motor (expressive) aphasia or another type occurs - sensory (or receptive).

 

Causes of the sensorimotor aphasia

With this type of speech disorder, sensory (receptive) aphasia and motor (expressive) are combined. Thus, this is complete or total aphasia - a serious disorder of the higher functions of speech, the causes of which are associated with the defeat of two speech (linguistic) areas of the cortex of the dominant (in right-handers - left) hemisphere of the brain at once.

Firstly, it is Broca's area located in the lower 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 desired algorithm (phonetic code) and transmits it to the controlling motor cortex articulation. [5]

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

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

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 disturbed due to 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 a stroke

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

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

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

Pathogenesis

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

With a brain tumor, its increase 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 to the superficial branches of the middle cerebral artery (arteria cerebri media), which provide blood to Broca's and Wernicke's zones, the mechanism of speech disorder is associated with a lack of oxygen and a deterioration in the trophism of these cerebral structures and part of the lateral cerebral cortex. [8]

Symptoms of the 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 problems with understanding the language.

Speech in sensorimotor aphasia can 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 spoken language; they cannot repeat what others have said and give an answer ("yes" or "no") to elementary questions.

There are often attempts at non-verbal communication through gestures and facial expressions.

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

Complications and consequences

Total aphasia is the most severe type 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 of the sensorimotor aphasia

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

Instrumental diagnostics includes:

• computed tomography of the brain ;
• magnetic resonance imaging (MRI) of the brain ;
• electroencephalography  (investigating the bioelectrical activity of the brain);
• dopplerography 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 with Alzheimer's disease.

Treatment of the sensorimotor aphasia

The treatment of receptive-expressive aphasia is to reduce the speech deficit during classes with a speech therapist, as well as to preserve 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

Read about the rehabilitation of the stroke field in the publication -  Post- stroke condition

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

Melodic Intonation Therapy (MIT) uses melody and rhythm to improve the patient's 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 unchanged auditory perception. [13]

Prevention

It is not yet known how to prevent damage to the speech areas of the cerebral cortex in traumatic brain injuries, stroke, and other conditions etiologically related to this speech disorder.

Forecast

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

However, symptoms of aphasia may improve over time, and language comprehension is usually recovered faster than other speech skills.