Dysarthria is difficulty in producing intelligible speech due to problems in the muscular control of speech-producing organs (such as the face, mouth, voice-box (larynx) and chest muscles). This can be due to damage to either the peripheral nerves, or the brain itself. Lots of things can cause the problem, including Parkinson’s disease (PD).
Why does is happen in Parkinson’s disease?
We know that Parkinson’s disease affects pathways in the brain which use dopamine as a signalling molecule. These pathways are primarily found in an area of the brain called the basal ganglia and are responsible for certain aspects of muscle control. In Parkinson’s disease, dopamine levels are depleted, resulting in motor symptoms such as tremor, stiffness and difficulty in initiating movements .
Speech problems in Parkinson’s disease result because these same processes affect the muscles involved in speech production. So lips become stiff and is unable to articulate the words, the tongue moves less freely, the larynx becomes stiff and unable to produce the desired volume of sound, the muscles of the thorax stop being able to push out the volume of air required to articulate long sentences. All these things combine to produce speech which is characteristically quiet, and lacking in changes in volume. Patients with Parkinson’s disease dysarthria also struggle to vary the pitch of their voice, speak in short rushes and produce imprecise consonants in a harsh, breathy voice . All of this combines to make speech difficult to understand by the listener.
How do Parkinson’s treatments work?
Treatment for Parkinson’s disease with both medicines and surgery can be very successful. Medical treatments were introduced following the discovery of depleted dopamine supplies in the brain. Medications either provide additional dopamine (as a pre-cursor molecule such as levodopa which is broken down in the area required), or block the pathways which naturally breakdown dopamine, so increasing levels. Treatments which do not interact with the dopamine pathways are also sometimes used in Parkinson’s disease – for example to reduce muscle stiffness.
Surgery for Parkinson’s disease was the first described treatment . Initially – and in some cases to this day – it involves removing affected areas of the brain on either one or both sides. This can produce significant improvement in the limb symptoms. However, significant side-effects and the irreversibility of treatment mean that other approaches have more recently been tired. Deep brain stimulation – where metal rods are placed into the problematic area and used to stimulate the nerves to produce more dopamine, can cause marked improvements in many patients .
What treatments have been tried in dysarthria and do they work?
In effect, all treatments for Parkinson’s disease have been tried in dysarthria, as 70% of patients with Parkinson’s disease will have dysarthria symptoms .
In early disease, dopamine treatments can be particularly successful, on both limb and speech related symptoms. Treatment with levodopa has importantly been found to improve the intelligibility of speech – as well as the volume and the measured strength of contraction in muscles such as the diaphragm . Unfortunately with all dopamine treatments it is common for complications and reductions in effectiveness to occur if they are continued for many years.
Sadly, other Parkinson’s disease treatments do not seem to be of particular help in treating dysarthria. Drugs which reduce dopamine breakdown, seem to have no effect, whist others may worsen the dysarthria. Only relaxant medications (such as clonazepam) may help in some aspects of speech generation in some patients – as they relax the lips and facial muscles allowing for easier word formation .
Overall medical therapies seem to have a very variable effect on dysarthria – and one which it is difficult to predict in individual patients.
Speech therapy is obviously a treatment specific to dysarthria in Parkinson’s disease. Many different treatment regimens and durations have been tried, but improvements – particularly in the longer-term, have only been poorly documented. Some studies suggest improvement in the short-term particularly with more intensive programmes. Although the movements of speech may become more fluid or more forceful, in many reports this is not translated into improved intelligibility of speech. One tool which does seem to provide all-round speech improvement is the Lee Silverman voice treatment (LSVT). This is an intensive programme designed specifically for people with Parkinson’s disease, and focused on increasing the volume of speech. Published data suggest improvements to speech volume, articulation and initiation which persist for at least one month, and maybe as long as two years .
Traditional surgical therapy seems to worsen dysarthria in Parkinson’s disease. In fact some procedures, such as thalamotomy (removal of the thalamus area of the brain) are no longer undertaken because of the realization of the effect they have on patients’ speech. No surgical procedure has been convincingly shown to improve dysarthria, with many making speech worse.
Deep brain stimulation is being increasingly used to treat the limb effects of Parkinson’s disease. One big advantage is that it can be stopped or altered if a patient shows worsening of their speech symptoms. Thus changes to deep brain stimulation of the internal globus pallidus are able to reverse some of the worsening of speech caused by the treatment . Deep brain stimulation of other areas, such as the subthalamic nucleus has been reported by some to improve speech . However, these reports are by no means universal, and even where scores on an assessment scale improve, the patient or their carers may not feel that the understanding of speech is better.
In summary then, surgery is clearly not the answer for dysarthria in Parkinson’s disease, and in many cases makes things worse.
Where to next?
Evolving treatments such as insertion of fetal brain cells to regenerate affected areas of the brain may offer improvements in dysarthria, although these have not yet been demonstrated . A much simpler approach – to inject collage into the vocal cords to make them more bulky and thus able to produce louder sounds may help in some patients .
Speech production is clearly very complex, involving the intimate interplay between motor control, the respiratory system and the thought process behind what to say. Understanding how these ‘go wrong’ in Parkinson’s disease, and how the dopamine pathways which we know are affected interact with the other involved systems is extremely difficult. For now, the treatment of dysarthria in Parkinson’s disease remains a challenging and frustrating process.
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