Communication disorders include disorders such as dyslalia, stuttering and the phonological disorder, better known as dysarthria . The basic sign that leads to the diagnosis of dysarthria is the presence of a marked difficulty in articulating phonemes adequately due to muscular problems.

In this article we will describe the causes and symptoms of the main types of dysarthria . We will also summarize the most common treatments for this disorder.

What is dysarthria?

Dysarthria is a disorder that affects the speech muscles : the lips, tongue, vocal cords and/or diaphragm. Difficulty in controlling these muscles or their weakness means that people with dysarthria cannot articulate their phonemes correctly, so they have pronunciation problems or speak more slowly than usual. Unlike motor aphasia, it is an alteration of pronunciation and not language.

The term “dysarthria” comes from Greek and can be translated literally as “articulatory malfunction”. It is a speech disorder and not a language disorder; this means that the problem does not occur at the cognitive level but at later stages of sound production. When the person is completely unable to articulate sounds we speak of anarthria.

The DSM-IV lists dysarthria under the label “Phonological Disorder” , while in the DSM-5 it is referred to as “Speech Sound Disorder”. The basic criterion for diagnosis under these classifications is that the person is unable to utter phonemes that he or she would be expected to learn to articulate by a certain age.

Causes of this disorder

Dysarthria can have many different causes. Among the most common are alterations of the nervous system, such as lesions and tumors in the brain or embolisms that paralyze the face or tongue. When it occurs from birth it is usually the result of cerebral palsy or muscular dystrophy.

Certain disorders favour the appearance of dysarthria symptoms in adulthood, such as amyotrophic lateral sclerosis or Parkinson’s, Huntington’s and Wilson’s diseases. Some drugs can also cause dysarthria, especially sedatives and powerful narcotics ; in these cases the interruption of consumption alleviates the disorder.

Symptoms and signs

The symptoms and signs of this disorder can vary depending on the cause and type of dysarthria. The following are among the most common:

  • Difficulty moving the muscles of the face, lips, and tongue
  • Mispronunciation .
  • Monotonous prosody.
  • Altered bell.
  • Speak too slow or too fast.
  • Nasal or hoarse voice .
  • Excessively high or low volume.
  • Irregular rhythm (e.g., slurred speech)
  • Associated breathing difficulties.

Four main types of errors are usually detected in relation to pronunciation difficulties: substitution, omission, insertion and distortion . Substitution, which consists of replacing the correct phoneme with an incorrect one, is the most frequent, especially when pronouncing “d” or “g” instead of “r”.

While consonant articulation is affected in all cases of dysarthria, improper pronunciation of vowels is considered an indicator of severity .

Types of dysarthria

The types of dysarthria that we will see in this section differ from each other mainly in the location of the lesion at the level of the central nervous system.

1. Spastic

Spastic dysarthria is due to lesions in the pyramidal tracts , related to fine motor control of the muscles of the face and neck.

In this type of dysphasia, hypernasality and sudden increases in the volume of speech occur. Vocalization tends to be strained and forced.

2. Ataxic

The lesions in the cerebellum cause ataxic dysarthria, whose most characteristic signs are the presence of a flat and monotonous prosody and a slow and uncoordinated vocalization , similar to that produced in the state of drunkenness. The speech typical of this type of dysarthria has sometimes been described as “explosive”.

3. Flaccid

In this type of dysarthria the vagus nerve is affected, which allows the movement of the larynx and therefore the vocal cords. Dysfunctions also occur in other facial muscles.

In cases of flaccid dysarthria, the muscles may atrophy or become partially paralyzed, causing spasms, drooling, and muscle tension.

4. Hyperkinetics

Hyperkinetic dysarthria is usually caused by injury to the basal ganglia, the subcortical structures involved in involuntary movements.

The symptoms of this type of dysarthria are similar to those of spasticity: the voice tends to have a harsh quality and hypernasality also occurs .

5. Hypokinetic

In general, hypokinetic dysarthria appears as a consequence of Parkinson’s disease , although it is also commonly caused by the continued consumption of antipsychotic drugs.

In this case the volume is usually very low, the timbre flat and the prosody monotonous. The reduced speed of movement caused by damage to the region known as the substantia nigra explains these symptoms.

6. Mixed

This category is used when the clinical features are a combination of more than one of the types of dysarthria we have described. Mixed dysarthria is due to impairments in different motor systems .

Treatment and intervention

The treatment of dysarthria depends largely on the disturbance that causes the disorder because, when possible, correcting the ultimate cause eliminates the symptoms . However, there are interventions to improve speech in cases where the underlying problem cannot be changed.

The main objectives of speech and language therapy in cases of dysarthria are to strengthen the muscles involved in speech, improve breathing, achieve proper pronunciation and facilitate communication between the affected person and those close to him/her.

In cases where speech is severely affected, external aids such as voice synthesizers and alphabetic charts are very useful. Learning gestures and even sign language can also serve to some extent to make up for the communication deficits typical of dysarthria.