That’s a short question, and one that’s difficult to answer as there are many possible causes.
The brief advice is to contact your doctor, who can assess what has happened; after that, it’s likely advisable to be referred to a speech and language therapist.
Background: Aphasia (the inability to either understand or produce speech) involves a loss of speech function, meaning, for example, that a person cannot understand speech or formulate language. In the early stages and for most of the course of Parkinson’s disease, aphasia does not occur at all. These language functions are part of the cerebral cortex, which is not affected by the disease process that causes Parkinson’s disease. The most common cause of aphasia is a stroke, in which case aphasia occurs very suddenly. Symptoms of aphasia may develop gradually over several years and are usually limited to certain functions or aspects of language, such as no longer being able to use a second language that one was previously able to speak. If it occurs early, either before or after the onset of motor symptoms typical of parkinsonism (stiffness, slow movements and tremors), this presentation may be consistent with Lewy body dementia. In very advanced Parkinson’s disease, after many years of having the condition, partial aphasia may develop, but it is quite rare for this to lead to significant communication problems.
It is considerably more common for other speech difficulties to occur in Parkinson’s disease. The most common is a low volume of speech – hypophonia – which makes it difficult to understand what the person is trying to communicate. Awareness of this is the most important thing, and it is worth bearing in mind that it is one’s own perception of one’s voice that is distorted – a person with Parkinson’s disease perceives the volume of their own voice as normal, but in reality it is low. It is possible to train this, and a specific method, Lee Silverman Voice Therapy, has a proven therapeutic effect that can be sustained over the long term if the technique is applied.
Other causes of speech difficulties include unclear speech, which is due to difficulties with articulation, known as dysarthria. It is sometimes possible to adjust treatment to improve articulation, but this can be difficult as it involves the coordination of around 20 (small) muscles that affects how speech is formed, and the need for medication for this function differs from that for, for example, walking, which depends on much larger muscle groups that are coordinated in a different way. Treatment with DBS (deep brain stimulation) can sometimes affect speech – both improving and impairing it – but it is usually possible to adjust the DBS settings to achieve clear speech.
There are also stammer-like symptoms – with difficulty getting past the first syllables of a word. This can be likened to ‘freezing of gait’ – ‘festination’, or the ‘freezing’ of one’s steps when about to start walking. This can often be improved through medication adjustments and speech and language therapy.
In extreme cases, where the disease is very advanced, or if there is a sudden interruption in regular medication, anarthria may occur (i.e. a complete inability to articulate). In such cases, it is also impossible to swallow, and medication must therefore be administered by means other than orally.
Håkan Widner