Dysarthria is by traditional definition a motor speech disorder that results from direct motor impairment to the muscles of speech production. This impairment may be from damage to the central portions of the nervous system contributing to a spastic paresis, from the peripheral portions of the nervous system contributing to flaccid paresis, or to the muscles themselves also mimicking flaccid weakness. In general the speech pattern in dysarthria will reflect the underlying neuromuscular difficulty and type of weakness. When the weakness is severe or very obvious, dysarthria is more likely to be accurately identified in children. Unfortunately, many cases of childhood dysarthria are not obvious. A significant body of literature exists, describing children who demonstrate spastic weakness only in the muscles associated with speech; primarily the lips, tongue, velum, and/or larynx. These muscle groups are very difficult to evaluate clinically, especially in young children who dont always cooperate with the adult oriented assessment tasks commonly used. For this reason, many of these children, who may present with severe speech deficits, are misidentified as demonstrating childhood apraxia of speech.
A primary consideration in distinguishing dysarthria in children from apraxia of speech is the presence or absence of vegetative impairments. These are easier to identify in children than spastic weakness in the lips, tongue, or velum. In general, we consider the tone, range, speed, and coordination of movements in speech, nonspeech oral, and vegetative tasks. The latter category may include performance in eating soft and masticated foods, and drinking from a cup, straw or other mechanism. Oral movement assessment needs to be tailored to the age and abilities of the child. Older children may participate willingly in a structured oral movement task (common movements used to evaluate oral apraxias). Younger children may be engaged in other activities such as sucking, blowing, or simple mimicry. Clinicians are obligated to bear in mind that these are not standard protocols and intended only to identify a pattern of movement impairment that may fit a specific neuromotor profile.
Though children with apraxia of speech will demonstrate dyscoordination during speech attempts and may demonstrate an accompanying oral apraxia, they should not demonstrate an overt neuromotor weakness and if any vegetative deficits are noted, they typically are more severe in the dysarthric child. A major clinical obstacle to more criteria driven identification of these clinical problems is the absence of a valid and reliability motor evaluation of the speech mechanism in children across the younger ages. Perhaps this will be remedied with future clinical research.
(Dr. Crary is a professor of Speech-Language Pathology in the Department of Communicative Disorders at the University of Florida. He has been specializing in disorders of swallowing and speech, primarily resulting from neurological impairment. Dr. Crary is the author of the highly referenced book, Developmental Motor Speech Disorders, as well as numerous other publications on neurogenic disorders. He has led important research studies in childhood apraxia and has lectured extensively on this topic. Additionally, he is a member of the Childhood Apraxia of Speech Association’s Professional Advisory Board.)