Karl E. Misulis, MD, PhD
The most common speech and language difficulties to come to the attention of hospital neurologists are aphasia and dysarthria. Important elements of language and hearing are presented here in overview, with subsequent more detailed discussion in later sections. Additional information on specific diagnostic entities is presented in chapters in Section III, Neurologic Diagnoses.
This chapter discusses the differential diagnoses of the following presentations:
•Aphasia: Deficit in language reception and/or expression of a variety of types
•Dysarthria: Impaired motor control of speech without an actual language deficit
•Hearing loss: Impairment in hearing due to neural degeneration (sensorineural) or mechanical (conductive) defects
Hearing loss can sometimes mimic receptive aphasia or even dementia, especially if the patient is not aware of the deficit or is not willing to report it.
APHASIA
Hospital neurologists will most likely see patients with three subtypes of aphasia: Global aphasia, Broca’s aphasia, and Wernicke’s aphasia, especially if in a stroke center. The aphasia is characterized by impairment of specific components of receptive and expressive language function. The following list presents some of the subtypes of aphasia and most likely responsible localizations.
FEATURES: Expression is impaired, but comprehension is relatively preserved except for impairment of small, grammatical word relationships.
LOCATION: Broca’s area, inferior frontal gyrus; most commonly middle cerebral artery (MCA) anterior division infarct
•Wernicke’s (receptive) aphasia
FEATURES: Speech is fluent but abnormal, with both sound (phonemic or literal) and meaning (verbal or semantic) errors (“paraphasias”), such that the language expression has deficient content. Comprehension of questions and commands is affected.
LOCATION: Temporal lobe, superior and middle region; most commonly MCA posterior division infarct
FEATURES: Deficits of comprehension and expression
LOCATION: Damage to both Broca’s and Wernicke’s area; usually MCA infarct, but also seen with inferior cerebral artery (ICA) occlusion, large left basal ganglia hemorrhages
FEATURES: Chief deficit is in repetition. Reception is relatively preserved although imperfect. Expression is paraphasic, in the literal or phonemic form.
LOCATION: Parietal lobe, supramarginal gyrus, occasionally temporal lobe
FEATURES: Prominent deficit in naming, beyond other language difficulties
LOCATION: Temporal lobe, not one specific region; can be seen with neurodegenerative diseases
FEATURES: Deficit in initiating speech but repetition and comprehension are preserved.
LOCATION: Anterior frontal region, either medial or lateral; anterior cerebral artery (ACA) territory strokes
•Transcortical sensory aphasia
FEATURES: Deficit in comprehension, similar to Wernicke’s aphasia, but with preserved repetition; speech is paraphasic.
LOCATION: Temporal-parietal or temporal-occipital junction; can be seen in stroke, occasionally in watershed strokes, mass lesions, neurodegenerative disorders
FEATURES: Deficit in both comprehension and expression but preserved repetition
LOCATION: Watershed region between Broca’s and Wernicke’s areas, not affecting either directly; can be seen in watershed strokes and also in advanced dementia
•Pure-word mutism (also called aphemia)
FEATURES: Inability to speak, with preserved ability to write; repetition can be preserved, and comprehension is also preserved. Overlaps with transcortical motor aphasia.
LOCATION: Frontal lobe, often directly in Broca’s area, sometimes seen in larger frontal lobe lesions, including tumor, trauma
FEATURES: Deficit in auditory comprehension but preservation of written comprehension; expression may be paraphasic.
LOCATION: Superior temporal gyrus, often bilaterally. Disconnection theory: disconnects the primary auditory cortices from Wernicke’s area
FEATURES: May have elements of receptive, expressive, or global aphasia depending on the location. Expressive aphasia with dysarthria is most common with basal ganglia lesions; fluent aphasia resembling Wernicke’s aphasia is most common with thalamic lesions.
LOCATION: Thalamus and/or basal ganglia
DIAGNOSIS of aphasia in the ED usually begins with emergent evaluation of suspected stroke. Detailed evaluation of stroke is discussed in Chapter 16. A computed tomography (CT) brain scan is often performed emergently, but a magnetic resonance imaging (MRI) scan is more likely to reveal the responsible lesion.
Etiologies of aphasia are multiple:
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