Understanding Childhood Apraxia of Speech

There is perhaps no other human attribute as dynamic, complex and powerful, as the gift of speech. Through it we communicate our thoughts and feelings, and develop deep human connections. Through it we also have the ability to forge relationships, and leave others with the imprint of the marks of our personality. Through it we create and experience the range of emotions that become our life experience.

Speech and sound disorders that occur in children can be classified according to causation. Using Shriberg’s Speech Disorders Classification System, speech disorders have been classified according to what causes them, as opposed to the historical various descriptive types or forms. The most recent version of Shriberg’s system proposes three distinct Speech Sound Disorders: Speech Delay, Speech Errors and Motor Speech Disorders. Motor Speech Disorders can be classified into three types: The Dysarthrias, which are conditions where the “execution” of speech is affected eg weakness of muscles used in speech production. Childhood Apraxia of Speech which is a Motor Speech Disorder affecting the preparation, or the “planning and programming” of speech, and Motor Speech Disorders not otherwise Specified. However, perhaps the most severe of the motor speech disorders is Childhood Apraxia of Speech, as it involves the highest levels of the motor speech system, and is thus a unique speech and sound disorder. Childhood Apraxia of Speech is also known in the United Kingdom as “Developmental Verbal Dyspraxia”.

Imagine not being able to put your thoughts into words, and not being able to communicate to those you care about simply because the mechanism of planning and programming the muscles of speech is not working at the level of the brain. This inability to do just that has been the subject of research over the last two decades, helping to increase our as yet incomplete understanding of this unique pediatric condition. Childhood Apraxia of Speech is just that… As defined by the American Speech and Hearing Organization :“Childhood apraxia of speech (CAS) is a neurological childhood speech sound disorder in which the precision and consistency of movements underlying speech are impaired in the absence of neuromuscular deficits (e.g. abnormal reflexes, abnormal tone). CAS may occur as a result of known neurological impairment, in association with complex neurobehavioral disorders of known and unknown origin, or as an idiopathic neurogenic speech sound disorder. The core impairment in planning and/or programming spatiotemporal parameters of movement sequences results in errors in speech sound production and prosody.”
(ASHA, 2007a, Definitions of CAS section, para. 1)

It is important to understand that Childhood Apraxia of Speech is a rare neurological condition , that is to say, a medical condition, not a developmental condition (ASHA, articles). This means that, in most cases, children are born with this condition, which is thought to have a genetic basis to it’s underlying cause. (Turner SJ, Hildebrand MS et al; Gordana Raca, B.S Baas et al) What this implies is that, as a parent, you could not have done anything differently to avoid or prevent this condition from happening to your child. The incidence of CAS is thought to be 1/1000, though some findings have shown this number to be up to 3-4 /100. CAS occurs on its own (idiopathic- no one knows why), or in the presence of other neurodevelopmental syndromes (eg Autism, Down’s Syndrome, Rett’s Syndrome, Galactosemia etc)

To help us understand the enormity of the extent of this speech disorder, understand that the activity of speech production involves a very complex process. In fact, there are about one hundred muscles involved in the process of speaking, and add to this,  each of them containing one hundred motor units. If a person speaks fourteen phonemes (sounds) per second, this adds up to 140 000 neuromuscular events per second. (Darley FL, Aronson AE, Brown JR: Motor Speech Disorders, Philadelphia, 1975, WB Saunders).  When we decide to say something, we simply say it. However, this entire process involves firstly conceptualization, or the intent or desire to say something, initiated by feelings, thoughts and ideas. Following this, language planning has to occur. This requires attention, focus, retrieval and working memory. All of this occurs in the dominant hemisphere of the brain, but is non motor in nature. Once this has happened, a plan to guide the movements necessary to actually create speech occur. Motor planning represents the highest level of the motor speech system, where it is decided what will be done. Following this, programming of the movements of speech occur, creating tactics on how to accomplish plans. It is thought that CAS is a disorder of both planning and programming of speech, therefore, at the level of the brain, however, in children no actual lesions have been identified, though researchers agree that this is where the problem lies.

Once planning and programming occur, the next step is the actual performance of speech, when pathways that originate in the brain are activated and stimulate the muscles of speech and the rest of the speech apparatus (tongue, pharynx, larynx, muscles, jaw etc) to actually move and create the sound and articulation that becomes what we say. Children learn this by sensory feedback. This entire process occurs seamlessly within seconds in unaffected individuals, however, in children with CAS, speech cannot occur to any intelligible degree without adequate treatment that targets this motor process of planning and programming. Motor speech processes, once learned, are stored to be recalled easily for future use. It’s very similar to learning how to do something with other muscles of your limbs, “practice makes permanent”. Similarly, with motor speech disorders such as CAS, repetitive practice improves the ability to plan and program to the point of this becoming an easier event and children thus becoming fluent speakers. However, this won’t “just” happen. It will take the efforts of repeated practice, and learning to train the brain to train the muscles of speech to make speech happen.

This forms the underlying basis of speech therapy for children with Childhood Apraxia of Speech.

Read More: Apraxia-KIDS.org: Definition of Childhood Apraxia of speech

Motor Speech newsletter pdf

References:
Joseph R. Duffy, Motor Speech Disorders, Chapter 2 Third Edition, Elsevier Publications.

ASHA.org/Policy 2007 Permission granted September 2015.

Maas E, Gildersleeve Neumann C.E., Jakielski K.J, Stoeckel R. (2014), Motor Based Intervention Protocols in the Treatment of Childhood Apraxia of Speech (CAS) Springer International Publishing.