Apraxia of Speech Features and Diagnosis

Apraxia of Speech (AOS) Definition & Features

• AOS is a neurogenic speech disorder that affects the motor planning and programming of movements for speech.
• AOS can range in severity from inability to speak to mildly imprecise or unnatural sounding speech.
• AOS can occur in both children and adults.
• Although AOS is less common than Aphasia, AOS is often seen alongside Aphasia. AOS is also sometimes seen alongside dysarthria.

AOS Diagnosis

• Diagnosis of AOS is based on a "perceptually derived cluster of behaviors" (McNeil et al., 2017, p. 201).
• The "kernel features" of AOS are sound distortions, extended segment and intersegment durations, and prosodic deficits.
• Sound distortions: These may be substitutions, distortions or distorted substitutions.
• Extended segment durations: These are lengthened productions of consonants and vowels which creates a slower perception of speech.
• Extended intersegment durations: These are lengthened pauses between sounds and words causing speech to appear segmented.
• Prosodic deficits: Individuals with AOS may have restricted alterations in pitch, intonation and loudness making their speech appear monotonous. They are also likely to show equal lexical stress.

Non-Discriminatory Features

• These features are often seen in AOS but are not considered "kernel" features.
• These features include: groping, effortful speech, difficulty initiating speech, awareness of errors, self-correction, variability of errors, increasing errors with word length, automatic speech is better than propositional speech, and islands of error-free speech.
• These features are not unique to AOS and therefore not reliable for diagnosis of AOS on its own.

Assessment Principles

• The goal of assessment should be to obtain information that will help you plan a therapy approach (Ballard et al., 2002).
• Assessment should include diadochokinesis, perceptual speech tasks, and observation for patterns of errors.

Diadochokinesis Assessment

• This is an assessment of the ability to make antagonistic movements in quick succession.
• There are two common diadochokinesis tasks
  • Alternating Motion Rates (AMRs): /ppppp//ttttt//kkkkk/
  • Sequential Motion Rates (SMRs): /ptk/ptk/ptk/ptk/
• These tasks assess the accuracy of articulation, speed and sequencing.
• SMRs will typically be worse than AMRs in AOS because they require increased motor planning.

Perceptual Speech Tasks

• Perceptual speech tasks include automatic speech tasks (e.g. counting 1-10, days of the week), repetition and imitation of various words and sentences as well as narrative or discourse samples.
• These tasks should be elicited with multiple repetitions to assess variability.
• Observe the client’s performance on automatic versus volitional tasks.
• Observe the client’s performance on repetition, propositional speech, and reading.
• Observe the client’s performance with a faster rate of speech, as errors may appear with increased rate.

Additional Assessments

• Assess overall speech intelligibility.
• Ask the client to provide a self-rating of their speech or of the effort required to speak.
• Conduct expressive and receptive language assessments to determine if aphasia is present.
• Conduct cognitive assessments and written language assessment.

Severity Assessment

• There is no standard method of assessing severity of AOS.
• Severity is typically rated subjectively by clinicians, based on judgement of speech quality.
• When rating severity, consider factors like intelligibility scores, frequency of errors in speech, percentage of sounds produced correctly, and subjective degree of effort of speaking.

Apraxia of Speech Rating Scale (ASRS)

• The ASRS is a recently published tool that is designed for description and quantification of characteristics indicative of AOS.
• It is a 5-point scale which describes presence or absence of particular speech characteristics, and their severity.
• The ASRS is divided into 16 items based on:
  • Discriminative of AOS
  • Apparent in AOS but also found in Aphasia
  • Apparent in AOS but also found in Dysarthria
  • Apparent in AOS but also found in both Aphasia and Dysarthria

Formal assessments

• The Apraxia Battery for Adults (ABA) is a widely used assessment used for AOS; however, it is based on diagnostic criteria that have been updated since the tool’s creation.
• ABA contains many useful tasks and stimuli for assessment.

AOS Recap

• Acquired neurogenic disorder of motor planning and programming of volitional movements for speech.
• Ranges in severity from inability to speak to mildly imprecise or unnatural sounding speech.
• Results from a variety of usually left hemisphere lesions.
• Frequently co-occurs with aphasia and less frequently with dysarthria.
• There are several standardized and non-standardized assessment options available to diagnose AOS.
• Assessment should consider performance on a battery of speech tasks, as well as examining the functional and psychosocial impact of disordered speech.