What Are Motor Speech Disorders?

The term "motor speech disorders" refers to a category of conditions occurring in childhood or adulthood that negatively affect a person's ability to create speech. Two subcategories of motor speech disorders are apraxia of speech, which is a difficulty in using the motor skills required to produce specific sounds, and dysarthria, or a weakness of muscles in the mouth. It can be hard to understand the speech of a person affected by motor speech disorders.

Dysarthria can occur in an individual for a variety of reasons. Traumatic events such as a brain injury or stroke can negatively impact motor skills. A variety of medical conditions can also cause dysarthria. Some of these conditions include brain tumors, amyotrophic lateral sclerosis or ALS, Guillain-Barre syndrome, Lyme disease, and Parkinson's disease.

Symptoms of dysarthria can vary depending on how and where the nervous system has been damaged. The speech of a person with dysarthria could be slow, slurred, rapid, hoarse, very soft, or sound like a monotone. A person could also have trouble chewing, swallowing, or controlling saliva. It is possible to experience temporary dysarthria as a result of using certain types of drugs, such as narcotics and sedatives.

Apraxia of speech, or verbal apraxia, should be distinguished from types of apraxia that affect other body parts such as the limbs. Verbal apraxia refers to trouble in putting speech sounds into the proper order for appropriate communication. Sometimes an individual with apraxia will inadvertently say words or nonsense syllables that are similar in sound to the target word. These individuals might be better at producing rote responses, such as customary greetings, than at delivering speech with a specific contextual meaning.

Childhood apraxia of speech is considered to be a distinct disorder. In this case, a child has the physical ability to create sounds with motor functions, but he or she needs help coordinating those motor skills to produce appropriate sounds on demand. These children might not have an age-appropriate spoken vocabulary and could seem frustrated by attempts to produce speech.

In some cases, different motor speech disorders can occur at the same time. Apraxia and dysarthria can occur together in some individuals, depending on the root cause. Verbal apraxia also sometimes happens simultaneously with aphasia, a condition in which brain damage affects language production.

The effects of motor speech disorders can diminish a person's ability to communicate effectively. In turn, this situation can lead to difficulties in social relationships. It is possible that a person with apraxia of speech or dyarthria could experience isolation and depression due to communication problems. A speech-language pathologist can assist individuals in retraining the speech muscles to produce desired sounds for communication.