Differential Diagnosis of Motor Speech Disorders – Key Vocabulary

A vocabulary set summarizing essential terms, tests, physiologic concepts, and ICF elements required for understanding and differentially diagnosing motor speech disorders.

Differential Diagnosis (Motor Speech Disorders)

The systematic process of narrowing possible causes and reaching conclusions about the specific motor speech deficit present.

Motor Speech Evaluation

An assessment in which the SLP matches perceptual speech findings to knowledge of the motor system to identify the disorder and plan treatment.

Speech-Language Pathologist (SLP) Role

Clinician who evaluates, differentially diagnoses, documents progress, and plans treatment for motor speech disorders.

International Classification of Functioning, Disability and Health (ICF)

WHO framework describing health conditions and their impact on body functions/structures, activity, participation, and contextual factors.

Body Functions and Structures (ICF)

Domain addressing physiological functions and anatomical parts; in MSDs it includes muscle or subsystem impairments like weakness or voice deficits.

Activity (ICF)

Execution of a task; for MSDs the activity is speech, with limitations reflected in reduced intelligibility, rate, or prosody.

Participation (ICF)

Involvement in life situations; communication participation can be restricted by motor speech disabilities, affecting social roles.

Contextual Factors (ICF)

Personal and environmental influences (e.g., age, technology, attitudes, noise) that can facilitate or hinder communication.

Motor Speech Disorders (MSDs)

Neurological speech disorders affecting planning, programming, control, or execution of speech, chiefly dysarthria and apraxia of speech.

Dysarthria

A group of motor speech disorders arising from impaired neuromuscular execution, producing abnormalities in strength, speed, range, steadiness, tone, or accuracy.

Apraxia of Speech (AOS)

A motor planning/programming disorder characterized by distorted substitutions/additions, segmentation, groping, and rate/prosody disruptions.

Upper Motor Neuron (UMN)

Neuron entirely within the CNS connecting cortex to brainstem/spinal cord; UMN lesions often create contralateral weakness patterns.

Lower Motor Neuron (LMN)

Neuron originating in the brainstem or spinal cord that innervates muscle; LMN lesions cause ipsilateral flaccid weakness.

Alternating Motion Rates (AMRs)

Rapid repetition of a single syllable (e.g., /pʌ/); assesses speed‐regularity and aids differential diagnosis (slow-regular in spastic, rapid-blurred in hypokinetic).

Sequential Motion Rates (SMRs)

Rapid repetition of a syllable sequence (e.g., /pʌtʌkʌ/); disproportionately worse SMRs than AMRs suggest apraxia of speech.

Assessment of Intelligibility of Dysarthric Speech (AIDS)

Standardized tool measuring intelligible words per minute to quantify dysarthria severity.

Frenchay Dysarthria Assessment

Formal battery assessing five speech subsystems, oral mech, and rating severity to aid differential diagnosis.

Newcastle Dysarthria Battery

Comprehensive tool with case history, subsystem and cranial-nerve assessment, characteristic charts, and treatment planning area.

Colorado Motor Speech Framework (MSF)

Assessment that evaluates five subsystems and cranial nerves, with neurologic symptom lists to facilitate diagnosis.

Perceptual Features Rating Chart

Subjective tool to rate severity across subsystems and note pathophysiology (e.g., weakness, spasticity) for diagnostic impressions.

Maximum Phonation Time

Longest duration a patient sustains /a/; reflects respiratory support and laryngeal valving (expected ≥9 s in adults).

Diadochokinetic Rates

Speed and regularity of repetitive syllable productions; informs about articulatory precision, VP closure, and respiratory/phonatory support.

Speech Intelligibility

Degree to which speech is understood by listeners; influenced by severity, strategies, listener familiarity, and task type.

Nonverbal Oral Apraxia

Deficit in volitional non-speech oral movements (cough, blow, click) often co-occurring with AOS; scored by accuracy and delay/groping.

ASHA Functional Communication Measure (FCM) – Motor Speech

Seven-level scale describing how speech production limits participation, coded for outcomes reporting (G-codes).

Intelligible Words per Minute

Quantitative severity metric obtained via AIDS; combines intelligibility and speaking rate.

Stimulability

Patient’s immediate ability to improve performance when given cues; guides prognosis and treatment hierarchy.

Utterance Length

Number of syllables spoken between breath pauses; shorter lengths indicate reduced respiratory support.

Speech Rate

Words or syllables per minute; abnormal fast or slow rates impact naturalness and intelligibility.

Velopharyngeal Function

Ability of soft palate to close nasal passage; tested via sustained /u/, “Make me a Hong Kong cookie,” and mirror under nares.

Hypokinetic Dysarthria

MSD associated with basal ganglia disease (e.g., Parkinson’s) featuring rapid/blurred AMRs, reduced ROM, and hypomimia.

Spastic Dysarthria

Speech disorder from bilateral UMN damage characterized by slow-regular AMRs, strained voice, and pathologic reflexes.

Flaccid Dysarthria

Dysarthria due to LMN damage with weakness, atrophy, fasciculations, and potentially hypernasality.

Ataxic Dysarthria

Cerebellar disorder producing irregular AMRs, scanning speech, and imprecise articulation with normal strength.

Hyperkinetic Dysarthria

MSD marked by adventitious movements and variable prosody, often from basal ganglia control circuit dysfunction.

Pathologic Reflexes

Exaggerated primitive reflexes (e.g., jaw jerk) indicating UMN involvement when present during assessment.

Fasciculations

Visible, involuntary muscle twitches characteristic of LMN lesions in flaccid dysarthria.

Central Facial Weakness

Lower facial weakness sparing the forehead caused by contralateral UMN lesion.

Tongue Deviation

Protruded tongue veers toward weak side; ipsilateral with LMN, contralateral with UMN lesion.

Respiratory Support

Capability to generate and sustain airflow/pressure for speech; evaluated via sniff, pant, utterance length, and cough.

Sound Pressure Level (SPL) Meter

Device or app that objectively measures loudness in dB during phonation, reading, or conversation.

Pairwise Variability Index (PVI)

Acoustic measure of vowel timing within polysyllabic words; reduced control of PVI helps distinguish AOS.

Errors with Increasing Word Length

Worsening accuracy as syllables increase (e.g., cat→catapult); sensitive indicator of apraxia of speech.

Health Condition (ICF)

Primary disorder or disease (e.g., stroke, Parkinson’s) associated with the motor speech impairment.