In right-handed people and about two thirds of left-handed people, language function resides in the left hemisphere. In the other third of left-handed people, much of language function resides in the right hemisphere. Cortical areas responsible for language function include
Posterosuperior temporal lobe (which contains the Wernicke area)
Adjacent inferior parietal lobe
Posteroinferior part of the frontal lobe just anterior to the motor cortex (Broca area)
Subcortical connections between those regions
Damage to any part of this roughly triangular area (eg, by infarct, tumor, trauma, or degeneration) interferes with some aspect of language function.
Prosody (quality of rhythm and emphasis that adds meaning to speech) is usually influenced by both hemispheres but is sometimes affected by dysfunction of the nondominant hemisphere alone.
Aphasia is distinct from developmental disorders of language and from dysfunction of the motor pathways and muscles that produce speech (dysarthria).
Etiology of Aphasia
Aphasia usually results from disorders that do not cause progressive damage (eg, stroke Overview of Stroke Strokes are a heterogeneous group of disorders involving sudden, focal interruption of cerebral blood flow that causes neurologic deficit. Strokes can be Ischemic (80%), typically resulting... read more , head trauma Traumatic Brain Injury (TBI) Traumatic brain injury (TBI) is physical injury to brain tissue that temporarily or permanently impairs brain function. Diagnosis is suspected clinically and confirmed by imaging (primarily... read more , encephalitis Encephalitis Encephalitis is inflammation of the parenchyma of the brain, resulting from direct viral invasion or occurring as a postinfectious immunologic complication caused by a hypersensitivity reaction... read more ); in such cases, aphasia does not worsen. It sometimes results from a progressive disorder (eg, enlarging brain tumor, dementia Dementia Dementia is chronic, global, usually irreversible deterioration of cognition. Diagnosis is clinical; laboratory and imaging tests are usually used to identify treatable causes. Treatment is... read more ); in such cases, aphasia progressively worsens.
Types of Aphasia
Aphasia is broadly divided into receptive and expressive aphasia.
Receptive (sensory, fluent, or Wernicke) aphasia: Patients cannot comprehend words or recognize auditory, visual, or tactile symbols. It is caused by a disorder of the posterosuperior temporal gyrus of the language-dominant hemisphere (Wernicke area). Often, alexia (loss of the ability to read words) is also present.
Expressive (motor, nonfluent, or Broca) aphasia: The ability to produce words is impaired, but comprehension and ability to conceptualize are relatively preserved. It is due to a disorder that affects the dominant left frontal or frontoparietal area, including the Broca area. It often causes agraphia (loss of the ability to write) and impairs oral reading.
There are other types of aphasia (see table Types of Aphasia Types of Aphasia ), which may overlap considerably. No aphasia classification system is ideal. Describing the types of deficits is often the most precise way to describe a particular aphasia.
Symptoms and Signs of Aphasia
Anomia (the inability to name objects) usually occurs in all forms of aphasia.
Patients with Wernicke aphasia speak normal words fluently, often including meaningless phonemes, but do not know their meaning or relationships. The result is a jumble of words or “word salad.” Patients are typically unaware that their speech is incomprehensible to others.
Auditory and written comprehension is impaired. Patients make errors in reading (alexia). Writing is fluent but has many errors and tends to lack substantive words (fluent agraphia).
A right visual field cut commonly accompanies Wernicke aphasia because the visual pathway is near the affected area.
Patients with Broca aphasia can comprehend and conceptualize relatively well, but their ability to form words is impaired. Usually, the impairment affects speech production and writing (nonfluent agraphia, dysgraphia), greatly frustrating patients’ attempts to communicate. However, spoken and written communication makes sense to the patient.
Broca aphasia may include impaired prosody and repetition, in addition to anomia. Writing is impaired.
Diagnosis of Aphasia
Differentiation from other communication problems
Bedside neurologic testing
Verbal interaction can typically identify gross aphasias. However, the clinician should try to differentiate aphasias from communication problems that stem from severe dysarthria or from impaired hearing, vision (eg, when assessing reading), or motor writing ability.
Initially, Wernicke aphasia may be mistaken for delirium Delirium Delirium is an acute, transient, usually reversible, fluctuating disturbance in attention, cognition, and consciousness level. Causes include almost any disorder or drug. Diagnosis is clinical... read more . However, Wernicke aphasia is a pure language disturbance without other features of delirium (eg, fluctuating level of consciousness, hallucinations, inattention).
Bedside testing to identify specific deficits should include assessment of the following:
Spontaneous speech: Speech is assessed for fluency, number of words spoken, ability to initiate speech, presence of spontaneous errors, word-finding pauses, hesitations, and prosody.
Naming: Patients are asked to name objects. Those who have difficulty naming often use circumlocutions (eg, “what you use to tell time” for “clock”).
Repetition: Patients are asked to repeat grammatically complex phrases (eg, “no ifs, ands, or buts”).
Comprehension: Patients are asked to point to objects named by the clinician, carry out one-step and multistep commands, and answer simple and complex yes-or-no questions.
Reading and writing: Patients are asked to write spontaneously and to read aloud. Reading comprehension, spelling, and writing in response to dictation are assessed.
Formal neuropsychologic testing Diagnosis by a neuropsychologist or speech and language therapist may detect finer levels of dysfunction and assist in planning treatment and assessing potential for recovery. Various formal tests for diagnosing aphasia (eg, Boston Diagnostic Aphasia Examination, Western Aphasia Battery, Boston Naming Test, Token Test, Action Naming Test) are available.
Brain imaging (eg, CT, MRI; with or without angiographic protocols) is required to characterize the lesion (eg, infarct, hemorrhage, mass). Further tests are done to determine the etiology of the lesion (eg, stroke evaluation Diagnosis Ischemic stroke is sudden neurologic deficits that result from focal cerebral ischemia associated with permanent brain infarction (eg, positive results on diffusion-weighted MRI). Common causes... read more ) as indicated.
Treatment of Aphasia
Treatment of cause
Augmentative communication devices
Treatment of certain lesions can be very effective (eg, corticosteroids if a mass lesion causes vasogenic edema). The effectiveness of treating aphasia itself is unclear, but most clinicians think that treatment by qualified speech therapists helps and that patients treated soon after onset improve the most.
Patients who cannot recover basic language skills and caregivers of such patients are sometimes able to convey messages with augmentative communication devices (eg, a book or communication board that contains pictures or symbols of a patient’s daily needs, computer-based devices).
Prognosis for Aphasia
Recovery is influenced by the following:
Size and location of lesions
Extent of language impairment
Response to therapy
To a lesser degree, the age, education, and general health of the patient
Children < 8 years often regain language function after severe damage to either hemisphere. After that age, most recovery occurs within the first 3 months, but improvement continues to a variable degree up to a year.
Language function resides in the left hemisphere in right-handed people and in two thirds of left-handed people.
Describe a particular aphasia by describing the types of deficits because types of aphasia overlap and no classification system is ideal.
Evaluate the patient's ability to name, repeat, comprehend, read, and write at the bedside, do brain imaging, and consider neuropsychologic testing.
Treat the cause when possible, and recommend speech therapy.