Cognitive impairment could affect the conversational ability of people with Parkinson's more than physical speech problems - according to research from the University of East Anglia (UEA) and the University of Aberdeen.
A new study published today is the first to assess the extent to which a patient's ability to think quickly forms a barrier to communication - rather than experiencing physical speech problems.
The research team found that physical speech problems are often less of a problem for patients than having the cognitive ability to keep up with conversations.
Parkinson's disease is a common neurodegenerative condition which affects around 1.5 per cent of people over 65 in Europe. The condition was originally characterised largely in terms of its motor features, however more recent research has revealed a wide range of non-motor symptoms including cognitive impairment in over a quarter of patients.
The research was carried out at UEA's School of Health Sciences and led by Dr Maxwell Barnish, who is now at the University of Aberdeen.
Dr Barnish said: "Around 70 per cent of people with Parkinson's have problems with speech and communication, which can really impact their quality of life.
"Researchers and clinicians have in the past focused on the physical problems patients have with making their speech clear. But patients themselves say the problems are more complex and are more to do with cognitive impairment - for example not being able to think quickly enough to keep up with conversations or not being able to find the right words.
"They say that this that this has the biggest impact on their ability to communicate in everyday life.
"We wanted to really prioritise the problems that patients experience - and to find out whether it is clarity of speech, or these more cognitive issues, that have the most impact on everyday communication."
The research team undertook the first systematic review to look at whether cognitive issues or physical speech problems create the biggest barriers to communication. They sifted through nearly 5,000 studies in search of helpful data, and found 12 relevant studies involving 222 patients.
They found that both cognitive status and physical speech problems are associated with everyday communication problems among people with Parkinson's. However patients who had greater cognitive difficulties, had more problems communicating. And while patients with less clear speech also had trouble communicating, this factor had less of an impact on everyday communication.
Dr Katherine Deane, from UEA's school of Health Sciences, said: "What this research tells us is that speech and language therapists need to assess the cognitive problems of people with Parkinson's as well as their speech clarity when trying to improve everyday communication. It may be that patients who are struggling with thinking quickly need different communication strategies to help them in everyday life.
"Before embarking on this research, we listened to the needs of patients, and found that much of the research to date had not prioritised what was really important to people with Parkinson's, their families, and their carers.
"Due to global ageing populations, Parkinson's should be considered a major healthcare challenge of the future, and it will become increasingly important to prioritise the needs of patients in research."
'Roles of cognitive status and intelligibility in everyday communication in people with Parkinson's disease: A systematic review' is published in the Journal of Parkinson's Disease on Friday, March 18, 2016.