Andrew Kirk, MD, FRCPC
DESCRIPTION
Aphasia is an acquired impairment of language characterized by word-finding difficulty and paraphasias with a variable disturbance of comprehension. In right-handed persons and most left-handers, aphasia results from a lesion in the left cerebral hemisphere. Occasionally a right-hander is seen with aphasia due to a right hemisphere lesion, a phenomenon known as “crossed aphasia.” The term “aphasia” refers to spoken language, but aphasics almost always have impaired reading (alexia) and writing (agraphia).
DEFINITIONS
- Paraphasias are errors in word production. They may be phonemic, with substitution of a wrong sound (“bup” for “cup”); semantic, with substitution of a wrong word that is often related in meaning (“dinner” for “cup”); or neologisms, with production of a meaningless non-word (“bitko” for “cup”).
- Fluency refers to the flow of speech and may be thought of as number of words per unit time or length of longest utterance. Nonfluent speech is halting, with long pauses and phrases shorter than 4 words. Fluent speech retains long phrases with a normal number of words per unit time.
- Nonfluent aphasics can often make themselves understood in a few words produced effortfully, while fluent aphasics often make very little sense despite lengthy output.
CLINICAL CHARACTERISTICS
- Aphasia is usually readily apparent during history-taking. The patient exhibits word-finding difficulty, resulting in paraphasias, circumlocutory descriptions (“that thing you write with” for “pen”), or obvious searching for words with pauses and filler phrases (“oh, um, you know”). Aphasia, a disorder of language, must be distinguished from other disorders of speech. Dysarthria is a disturbance of articulation due to lesions lower in the nervous system. Although aphasia and dysarthria may coexist, a patient with only dysarthria should be able to read and write normally. Dysphonia, a disturbance of voice, may be due to problems with the larynx or its innervation.
- Aphasia must also be distinguished from more diffuse disturbances of cerebral function, such as delirium, where attention and other cognitive abilities are also affected.
PATHOPHYSIOLOGY
- Language centers surround the left Sylvian fissure within territory supplied by the middle cerebral artery (MCA). Figure 1, “Lichtheim's house,” presents a schematic of language processing based on the work of Lichtheim. While obviously a gross oversimplification of a complex process, it nonetheless serves as a useful tool for bedside assessment of aphasia. Auditory input (I) is presented to Wernicke's area (W) in the posterior third of the superior temporal gyrus where sounds heard are linked to representations of words that Lichtheim called “auditory word engrams.” Broca's area (B) in the inferior frontal gyrus programs lower centers to articulate a word, producing speech output (O) and may be thought of as containing Lichtheim's “motor word engrams.” Broca's area is also important in producing correct word order so that sentences make grammatical sense. Wernicke's and Broca's areas are connected by white-matter tracts such as the arcuate fasciculus (line W–B). Lichtheim visualized an extra-Sylvian area of concepts (C) where engrams were linked to actual meanings of words and, while there is no one brain area corresponding with this, C may be thought of as the rest of the cerebrum, beyond left MCA territory.
- Lesions disrupting the line C–B–O impair fluency. Lesions along I–W–C impair comprehension. Repetition is affected by lesions along I–W–B–O.
DIAGNOSTIC TESTS AND INTERPRETATION
Imaging
Initial Approach
- Imaging studies
- CT or MRI scanning is useful to confirm the location and nature of the causative lesion.
- Bedside examination is generally sufficient to determine aphasia type and severity, but numerous standardized aphasia test batteries provide more detailed assessment. These range from 3- to 10-minute screening tests, such as the Frenchay Aphasia Screening Test, to the Boston Diagnostic Aphasia Examination which can take several hours. In 45 minutes, the Western Aphasia Battery determines the type and severity of aphasia.
DIFFERENTIAL DIAGNOSIS
Aphasia is most often due to ischemic or hemorrhagic stroke within or adjacent to the territory of the left MCA but may result from trauma, tumor, infection, or other lesions in this location. Aphasia is uncommon with external compressive lesions such as subdural hematoma. A hemiparetic patient with aphasia is thus likely to have an intraparenchymal rather than an extraparenchymal lesion. Language disturbance is often present in dementias such as Alzheimer's disease and is often prominent in frontotemporal dementia, types of which are often termed “primary progressive aphasia.” Progressive nonfluent aphasia presents with impaired fluency and usually agrammatisms, phonemic paraphasias, and anomia. In semantic dementia, speech is fluent but meaning is lost with impaired naming and comprehension. Paraphasias are generally semantic. Although deficits in primary progressive aphasia may be confined to language for quite some time with relatively preserved day-to-day functioning, later in the illness, frontal and temporal degeneration take their toll in the form of further behavioral disturbances. Although usually sporadic, frontotemporal dementia can also be inherited.
SIGNS AND SYMPTOMS
- Patients’ spontaneous speech reveals paraphasias and word-finding difficulty and is also used to judge whether they are fluent or nonfluent. Naming is tested by showing patients objects. Patients with mild aphasia may name common items well but have more difficulty producing less common words such as parts of objects. Thus, aphasics tend to have more difficulty naming a watch strap than a watch. Comprehension is tested by asking the patient to carry out commands of varying levels of difficulty. One can begin with a simple one-step command and progress to complex three-stage commands. Repetition is tested beginning with single words and progressing to complex phrases such as “no ifs, ands, or buts.”
- Peri-sylvian aphasias (Broca’s, Wernicke’s, conduction, and global) are typically due to infarcts in left MCA territory and since all disrupt I–W–B–O, they have in common a disturbance of repetition.
- Broca's aphasia
- A lesion in Broca's area (B) causes nonfluent speech with poor repetition but relatively preserved comprehension, particularly for nouns and verbs. Since Broca's area is adjacent to the precentral gyrus, this is usually accompanied by right hemiparesis.
- Wernicke's aphasia
- A lesion in Wernicke's area (W) results in fluent speech with impaired comprehension and repetition. Although it may be accompanied by a right superior homonymous quadrantanopia due to involvement of temporal fibers of the optic radiations (Meyer's loop), Wernicke's aphasia is not typically accompanied by hemiparesis. Due to the paucity of other findings on examination, it is not unusual to see a patient referred with “confusion” who actually has Wernicke's aphasia.
- Conduction aphasia
- A lesion between Wernicke's and Broca's areas in the arcuate fasciculus/insular area (W–B) results in fluent speech with good comprehension but poor repetition.
- Global aphasia
- A large MCA infarct causes nonfluent speech with poor comprehension and repetition and is typically accompanied by severe hemiparesis. Global aphasia unaccompanied by hemiparesis suggests multiple lesions sparing motor cortex, often of cardioembolic or metastatic origin.
- Transcortical aphasias
- These result from lesions in the watersheds between middle, anterior, and posterior cerebral arteries (ACA and PCA) or within ACA or PCA territory, disconnecting peri-Sylvian language centers from the rest of the cerebrum. Watershed infarcts may result from hypotension, a shower of small emboli, or carotid occlusion. During cardiac surgery, either of the first two of these conditions may occur, and this is a typical clinical setting for transcortical aphasia. Because peri-Sylvian language areas are spared, repetition is intact.
- Transcortical motor aphasia
- A frontal lesion outside Broca's area (C–B) results in a language deficit similar to Broca's aphasia except that repetition is intact.
- Transcortical sensory aphasia
- Temporo-parieto-occipital junction lesions (W–C) may result in an aphasia similar to Wernicke's except that repetition is preserved.
- Mixed transcortical aphasia
- An aphasia similar to global aphasia but with preserved repetition may result from a large MCA/PCA/ACA watershed infarct (C–B and W–C).
- Anomic aphasia
- Impairment of naming with good comprehension, repetition, and fluency is a common but poorly localizing aphasia type. Lesions in many left cerebral areas my cause this mild aphasia.
- Subcortical aphasia
- Lesions in left thalamus or subcortical white matter may cause aphasia syndromes rather similar to the cortical aphasia types described above. Associated deficits may be atypical (e.g., Wernicke's like aphasia with dense hemiparesis). These patients are often quite dysarthric, and repetition is often relatively preserved. Particularly with thalamic lesions, patients may fluctuate dramatically between near-normal output and mumbled jargon.
MEDICATION
First Line
- Drug(s) of choice
- Although some reports have suggested improved speech output with bromocriptine or stimulants, specific pharmacotherapy of aphasia has been disappointing and is not generally used.
ADDITIONAL TREATMENT
General Measures
The underlying lesion type determines overall management. Acute aphasia due to ischemia may be amenable to thrombolytic therapy. Time is thus of the essence in evaluation.
SURGERY/OTHER PROCEDURES
- Determined by the underlying lesion.
- Symptomatic treatment
- Determined by underlying lesion. Patients with poor comprehension often benefit from being told information repeatedly and in different words.
- Adjunctive treatment
- Large trials suggest that speech therapy by speech pathologists improves recovery.
IN-PATIENT CONSIDERATIONS
Discharge Criteria
Usually determined by the underlying lesion.
FOLLOW-UP RECOMMENDATIONS
Usually determined by the underlying lesion.
Patient Monitoring
Usually determined by the underlying lesion.
PATIENT EDUCATION
Family members benefit from an explanation of language impairment. They often do not understand that patients’ answers may not reflect true understanding of questions asked. National Aphasia Association. Website: www.aphasia.org
PROGNOSIS
Aphasia following stroke generally improves the most in the first 3 months but may continue getting better at a slower rate for 1–2 years. Global aphasia often evolves into Broca’s, while Wernicke's may become conduction or anomic during recovery.
