Differential Diagnosis of CAS
What are the most robust indicators of CAS?
For many years the existence of CAS was debated and opinions differed about the nature and characteristics of the disorder. In 2007, ASHA released a technical report and position statement on CAS, recognizing the existence of the disorder and describing the characteristics. Since then researchers have continued to study CAS. Today, many experts agree that CAS results from a neurologically based difficulty with motor planning and programming for speech production with the following characteristics being more likely to discriminate CAS from other types of speech sound disorders:
- Difficulty moving from one articulatory configuration to another
- Presence of vowel distortions
- Groping and/or trial and error behavior, especially in elicited versus spontaneous utterances
- Prosodic errors including lexical stress errors, equal stress and segmentation of sounds/syllables all of which can make speech sound "robot like" and decrease intelligibility
- Inconsistent voicing errors making it difficult to distinguish voiced/unvoiced phonemes likely due to mistiming of voice onset time.
What should be included in my assessment?
A motor speech examination is a critical component in an assessment for CAS because it allows the clinician to observe speech production and behaviors associated with CAS in utterances that vary in length and complexity. In a dynamic motor speech exam the clinician provides cues to facilitate performance which can be even more helpful because:
- It enables the clinician to observe what the child can do when attention and effort is focused on imitating and using cues provided by the clinician
- It allows the clincian to observe behaviors assoicated with CAS, such as groping, that may only occur when the child attempts longer or move difficult utterances
- It can facilitate judgements about severity and prognosis by observing the child's response to cues.
- It can help with treatment planning, such as the type and number of word targets to select and the cueing methods that will be most helpful to the child.
What tests are available to diagnose CAS?
There are several tests used to diagnose CAS, but not all have evidence of both validity and reliability which are important considerations for evidence-based practice. In a systematic review of tools used to assess CAS, Gubiana M.B., Paglianrin, K.C., et. al. (2015) reported on the validity and reliability of several CAS test. See a summary of the review here.
- Dynamic Evaluation of Motor Speech Skills (DEMSS) - evidence of both validity and reliability
- Verbal Motor Production Assessment for Children (VMPAC) - partial evidence of validity
- Kaufman Speech Praxis Test (KSPT) - partial evidence of validity
What if I am not sure?
Diagnosis of CAS can be challenging. Children with CAS often have concomitant language and phonologic disorders, and young children may have difficulty participating in evaluation procedures. All of these factors can make it difficult to confidently diagnose CAS. In such cases, clinicians may use a descriptive diagnostic statement that documents CAS cannot be confirmed or ruled out, followed by a list of characteristics observed in the assessment. Clinicians may also want to try a motor-based therapy approach and carefully monitor the child’s response to treatment. A robust response to a motor-based treatment approach suggests that motor planning may be an area of difficulty for the child.
Dr. Edythe Strand Discusses Key Topics in Assessment of CAS
CAS Assessment Plan
Discriminative Characteristics of CAS
Dynamic Motor Speech Exam