Aphasia is a condition caused by brain damage that affects a person’s ability to use language correctly.
In aphasia, parts of the brain involved in speaking, reading, writing and comprehension are damaged.
These brain regions are known collectively as the brain’s language center and loss of function occurs in the cerebral cortex and basal ganglia or the pathways that connect them.
This brain damage is usually caused by stroke and almost all patients with stroke develop some degree of aphasia.
Other common causes include severe head injury, brain tumor and the neurodegenerative condition Alzheimer’s disease.
Aphasia has no effect on a person’s intellectual ability. Individuals with the condition remain fully alert and can think clearly, but find their speaking, reading and writing abilities are affected.
Aphasia sufferers know what they want to say, but find it difficult to express their thoughts in words, sometimes using the wrong sounds to say a word or assembling their sentences incorrectly.
Reading and comprehension are affected in a similar way, with sufferers finding it difficult to understand the words or sentences they are trying to read or listen to. People with aphasia may also find it difficult to use numbers or perform calculations.
Aphasia usually develops suddenly, but sometimes it can develop gradually, in which case it is referred to as primary progressive aphasia.
This form of aphasia is not caused by stroke, head injury or a brain tumor, but by degenerative diseases that progress slowly, gradually causing nerve cells to die.
The most common causes of primary progressive aphasia are frontotemporal lobar degeneration and Alzheimer’s disease.
Aphasia can be a very frustrating and confusing condition to live with as many intelligent and alert individuals are suddenly thrown into a world of jumbled communication.
Aphasia is diagnosed based on detailed tests to exclude other communication disorders; neuropsychological testing and brain imaging studies.
For a clinician to be sure of an aphasia diagnosis, they need to eliminate any possibility that the symptoms are being caused by the motor speech disorder dysarthria or by impaired hearing, vision or motor writing ability.
Patient assessment in cases of suspected aphasia should include the following:
- Naming ability is assessed by asking patients to name objects. The clinician will use descriptions of objects to prompt the naming response such as “What you use to drive somewhere…”
- Spontaneous speech is assessed for fluency, the number of words used, speech initiation, error rate, hesitation and speech style characteristics.
- Repetition ability is tested by asking the patient to repeat a complex sentence.
- Reading and writing ability are tested by asking the patient to read out loud and write something down. The patient’s ability to spell and write correctly in response to dictation are also assessed.
- Comprehension is tested by assessing the patient’s ability to point at objects the clinician names, to carry out tasks and to answer both simple and complex questions with a “yes” or “no” response.
A neuropsychologist or speech therapist may perform cognitive testing to check for finer dysfunction. This can give an indication of how likely recovery is, as well as helping to optimise any treatment plans.
Examples of tests that may be used include the Boston Diagnostic Aphasia Examination, the Token Test, the Western Aphasia Battery and the Action Naming Test.
Once aphasia has been diagnosed, imaging studies are performed to reveal the extent of any brain damage.
Examples of these tests include a computerized tomography (CT) scan and a magnetic resonance imaging (MRI) scan.
These tests are used to characterize any lesions such as a tumor, hemorrhage or infarction.
Positron emission tomography (PET) may also be used to assess processes such as blood flow, dopamine release or inflammation in the brain.
This allows the examiner to check the overall state of the brain and can be useful in evaluating aphasia caused by progressive diseases such as Alzheimer’s.