Differential diagnosis of pediatric motor speech disorders is challenging for a number of reasons, including the interaction of language and speech in acquisition, co-existing disorders, and complicated syndromes. Our training has provided us skills in administering tests and other assessment tools, but more likely in the areas of language and phonology than motor speech. What if the child has very little or no speech, or can’t participate in standardized testing?
Even if we feel competent in administering assessment tools, the interpretation of a child’s responses on any task is often challenging, both with respect to differential diagnosis as well as treatment planning.
Using a Framework to Overcome Assessment Challenges
Having a framework for assessment helps overcome these challenges. That framework would involve:
- A working knowledge of current taxonomies for speech sound disorders and those characteristics associated with each label
- Experience with making observations in non-structured spontaneous speech for comparison to those in standard and structured, but non-standard tasks
- Practice in interpretation of responses during structural-functional exams and motor speech exams
- Methods to detect “red flags” for children too young or otherwise unable to participate in assessment tasks
Is CAS Contributing to the Disorder?
One of the biggest challenges in differential diagnosis of pediatric motor speech disorders is recognizing the degree to which childhood apraxia of speech (CAS) may be contributing to the child’s speech disorder. CAS generally reflects deficits in the processes involved in speech motor programming — the specification of which muscles need to contract so that specific respiratory, laryngeal, and oral articulatory structures move to the right place at just the right time.
Comparing Observations of Both Speech and Non-Speech Behavior
Proprioceptive processing and motor speech planning/programming are likely to be involved, but direct measurement of each is not yet possible. Clinicians must compare observations of speech and non-speech behavior to currently accepted diagnostic markers, associated with specific labels for different subtypes of speech sound disorders.
Characteristics Representative of CAS
Differentiating childhood apraxia of speech (CAS) from phonologic impairment and/or dysarthria is especially challenging. However, there is some consensus regarding characteristics that are associated with this label, including:
- Impaired precision and consistency of the movements creating the acoustic signal
- Inconsistent errors on consonants and vowels in repeated productions of syllables or words
- Lengthened and/or disrupted co-articulatory transitions between sounds and syllables
- Inappropriate prosody (incorrect lexical or phrasal stress and/or segmentation)
Discriminative and Non-Discriminative Characteristics
While these characteristics represent the core observations consistent with the diagnosis of CAS, other characteristics may often be present although not discriminative. Additional characteristics may prove discriminative as ongoing research focuses on the validity of diagnostic markers.
Often present but not discriminative:
- Limited consonant and vowel repertoire
- Use of simple syllable shapes
- Frequent omission of sounds
May be discriminative:
- Difficulty moving from one articulatory configuration to another
- Groping and/or trial and error behavior
- Presence of vowel distortions
- Prosodic and mistiming errors
CAS Is a Speech Disorder
It is especially important to keep in mind that CAS is just a label for a subset of children with speech sound disorders — it’s not neuropathy. Even though the speech problem is due either to known brain disorders or undetermined inefficiencies in the neural processes involved in programming speech movement, it is a speech disorder.
That label will likely change as the child’s speech characteristics adjust with neural maturation and therapy. Typically, children with CAS also exhibit phonologic impairment because their motor speech deficit will undermine the child’s ability to learn and practice the rule-governed system of sounds associated with language.
The Importance of Developing Good Clinical Thinking Skills
Developing good clinical thinking skills can help clinicians face these challenges. In assessment, we begin by forming clinical hypotheses based on the child’s medical, developmental, and therapy history. Our initial observations as we meet the child, watch them communicating with parents, and begin to develop rapport also inform this process. We then choose assessment tasks and/or standard instruments to test those hypotheses in order to come to a differential diagnosis and treatment plan.
Using Both Structural-Functional and Dynamic Motor Speech Exams
The structural-functional exam and a dynamic motor speech exam — especially the interpretation of the child’s responses on these tasks — are important tools for differential diagnosis of pediatric motor speech disorders. Dynamic assessment of motor speech is especially important, as observations of responses to cueing allow the clinician to view additional behavioral characteristics consistent with the label CAS. Dynamic assessment also provides much more information regarding severity and prognosis and more specific help in treatment planning.