The role of the dominant hemisphere
The speech area is in the left, dominant side of the brain in about 99% of right-handed people. The remaining 1% may be naturally left-handed people who have been forced to write with their right hand. The brain’s right hemisphere is the dominant side in only 30% of left-handed people. This means it is rare for a stroke that causes weakness on the left side of the body to damage the speech area. Speech damage from a stroke affects almost no right-handers and only 30% of left-handers.
As a general rule, a lesion of the left hemisphere will cause dysphasia. A lesion in the right hemisphere will cause neglect, visuo-spatial and cognitive problems. The cause is damage or disease of the brain and so it is most common in old people. Diseases could be degenerative, tumours or growths, or blood vessel problems. Around 85% of cases arise from a stroke. Around a third of people who have a stroke will have dysphasia. In younger people it is usually a result of head injury.
Causes of dysarthria
Dysarthria is caused by upper motor neurone lesions of the cerebral hemispheres, or lower motor neurone lesions of the brain stem. It also results from disruption to the way the upper motor neurones, basal ganglia and cerebellum work together.
Features of dysarthria
These may vary depending upon the site of the lesion:
- Slurred and weak articulation with a weak voice is typical of inability to move facial muscles (pseudobulbar palsy) after a stroke. Other neurological signs are usually unilateral with a right-sided hemiplegia (left side of brain). It may be on the left in a minority of left-handers. Brain stem stroke may lead to bilateral signs with dysarthria or anarthria.
- Slurred, scanning and staccato speech caused by cerebellar lesions is typical of multiple sclerosis.
- A dysrhythmic, dysphonic and monotonous voice is caused by Parkinson’s disease. People with PD have stiff, rigid movement and that includes how the vocal chords create sound (phonation).
- Indistinct articulation, hypernasality and bilateral weakness caused by lower motor neurone disorders can occur with motor neurone disease.
Management of dysarthria
The bulbar and facial muscles are best assessed and treated by a speech and language therapist, who can create a programme of exercises to improve muscle tone and movement to match the person’s needs. Be patient with a dysarthric person and try to understand what they are communicating. This encourages them to make an effort rather than give up. If speech is still too difficult, they may find it easier write or use an electronic communicator if they have one.
Causes of dysphasia
Dysphasia is impaired ability to understand or use the spoken word. It is caused by a lesion of the dominant hemisphere and may include impaired ability to read, write and use gestures. The commonest cause is cerebrovascular disease, but it can arise from a space-occupying lesion, head injury or dementia.
Features of dysphasia
Dysphasia can be seen as a disruption in the links between thought and language. The diagnosis is made only after excluding sensory impairment of vision or hearing, perceptual impairment (agnosia), cognitive impairment (memory), impaired movement (apraxia) or thought disturbance (as in dementia or schizophrenia). When a person is being tested for dysarthria and dysphasia, their ability to repeat or produce difficult phrases or tongue twisters can be indicative.
- People with receptive dysphasia often have language that is fluent with a normal rhythm and articulation, but it is meaningless as they fail to comprehend what they are saying.
- People with expressive dysphasia are not fluent and have difficulty forming words and sentences. They will make grammatical errors and have difficulty finding the right word. In severe cases they do not speak spontaneously, but they usually understand what is said to them.
Specific types of aphasia are associated with damage to particular regions in the brain, but in practice distinctions are not always clear. Language is a complex activity involving many areas of the brain and lesions do not dissect clearly demarcated anatomical areas. Generally, expressive dysphasia suggests an frontal lesion, while receptive dysphasia suggests a rear lesion. There are a number of sub types. They are:
- Sensory (Wernicke’s) aphasia – the primary symptoms are general difficulty in comprehension, difficulty in retrieving words and saying unintended or incorrect syllables, words, or phrases. This type of aphasia damages the semantic content of language while leaving the language production function intact. The consequence is a fluent or receptive aphasia in which speech is fluent but lacking in content. Patients lack awareness of their speech difficulties.
- Production (Broca’s) aphasia – this is a non-fluent or expressive aphasia since there are deficits in speech production, speech functions such as tone, stress and rhythm, and comprehension of grammar. Patients will typically exhibit slow and halting speech, but with good semantic content. Comprehension is usually good. Unlike Wernicke’s aphasia, Broca’s patients are aware of their language difficulties.
- Conduction aphasia – symptoms include difficulty naming things, and inability to repeat non-meaningful words and word strings. But the person will have apparently normal speech comprehension and production. Patients are aware of their difficulties.
- Deep dysphasia – symptoms are word repetition problems and semantic paraphasia (substituting a semantically related word when asked to repeat a target word).
- Transcortical sensory aphasia – symptoms are impaired comprehension, naming, reading, writing and semantic irrelevancies in speech.
- Transcortical motor aphasia – symptoms are transient mutism (fleeting inability to speak), monotonous speech and leaving out unimportant words.
- Global aphasia – this results in extensive symptoms that include generalised deficits in comprehension, repetition, naming and speech production.
Examining a person with dysphasia
Tests for receptive dysphasia may include asking the person to read words or a passage and then asking them to explain it. Comprehension of spoken material is assessed by asking the person to listen to a passage and explain it or, alternatively, by asking them to follow certain instructions such as, “point to the door”.
Tests for expressive dysphasia include:
- Asking the person to name a series of objects and some of their parts. For example, asking: “What is this?”, pointing to a pen, your tie and watch in turn. Then asking: “What part of the watch is this?”, pointing to the strap and then the face or hands.
- If language is limited then dysphasia may be tested by holding up a pen and asking, “Is this a pen?” If the person says, “Yes”, then point to your watch and ask, “Is this a pen?” This demands a different reply. Look out for difficulty in finding the right word and inappropriate repetition of the same word or phrase.
- Can the person talk spontaneously on a familiar topic? “Tell me about your family.” “Tell me about the work you used to do”.
- Can the person count numbers or recite days of the week?
- Can they write a brief dictated passage?
- Can they write a brief spontaneous passage?
- Can they copy a short passage?
All tests of literacy and numeracy must be interpreted in the light of how the person was before the onset of such problems. For example, impairment in numeracy in a former accountant probably represents a substantial decline.
Management of dysphasia
Referral to a speech and language therapist is the usual practice. The therapist can carry out a thorough assessment of the nature of the problem and draw up a set of exercises to encourage the recovery of fluent speech and understanding. Therapy tends to be tailored to the needs of the individual patient. The value of these interventions has been assessed by a Cochrane review that concluded that, while there was no good evidence to support such management, there was none to refute it either. The problem is a shortage of good-quality research to assess the value of speech and language therapy.
Aphasia may have a severe, debilitating effect on the person’s everyday life. Severe aphasias are likely to show little improvement, but other forms can show rapid improvement. The probability of recovery following trauma is higher than following stroke. Around one-third of people with aphasia recover fully within three months, but complete recovery is unlikely after six months. When language returns in a person who was an immigrant but has spoken English for many years, it tends to return in their native language. There is a possibility that some drugs may enhance the ability to learn and hence to recover language after a stroke, but this is still very much in the experimental stage.