Psychology’s role in the Parkinson’s pandemic

First described as 'shaking palsy' by James Parkinson just over 200 years ago – and later renamed in his honour by Jean-Martin Charcot – Parkinson's disease is the most rapidly growing neurological condition in the world today. 

While global life expectancy doubled between 1900 and 2000, this factor alone is far from explaining the increase in this age-related disease. The Parkinson's population worldwide in fact doubled in just 25 years, from 2.6 billion in 1990 to 6.3 billion in 2015. And this figure – which is far higher than for Alzheimer's or other age-related conditions in the same period – is projected to double again by 2040. 

Why the alarming increase in less than 30 years? For decades, the aetiology of Parkinson's has been considered idiopathic – roughly translated: 'who knows?'. This is the first myth that Ending Parkinson's Disease challenges. Epidemiological evidence from the past few decades has identified a number of environmental factors linked to higher risk of developing the condition, including pesticides (e.g., paraquat, DDT), common chemical solvents (e.g., trichloroethylene, rotenone), and excessive air pollution. A few of these substances are now banned around the world, but some (like paraquat, which increases the risk of Parkinson's by 150 per cent) are still widely used in the US. And the adoption of others, like trichloroethylene, is consistently on the rise in developing countries like China, where the prevalence rate of Parkinson's since 1990 has increased by a staggering 116 per cent against the 22 per cent increase worldwide. 

Causal associations with environmental factors are of course not unequivocal. There are also known personal predispositions to add to the equation – like ageing (the biggest risk factor), genetic mutations (thought to be responsible for around 10 per cent of new diagnoses), history of repeated concussions (consider Muhammad Ali), and lack of exercise. However, the current evidence, coupled with the observation that the disease does not occur naturally in non-human animals, suggests that Parkinson's may be – at least partially – caused by humans, and therefore partially preventable.

In fact, the authors say that the recent increase of the Parkinson's population may represent the first sign of a preventable pandemic – one fuelled by overreliance on noxious chemicals and lack of advocacy against risky policies and behaviours. Drawing inspiration from the movements that fought against polio, HIV, and breast cancer, they propose a 'PACT to Prevent the disease, Advocate for policies, Care for patients, and Treat the condition with innovative therapies'. This is coupled with a 'prescription for action' which, although focused on the US context, encourages readers to take personal action. 

To support their PACT, the authors share inspirational stories of patients and caregivers, and the expertise of clinicians from a wide range of healthcare professions. Among the latter, psychology is by far the most notable absentee, with no mention in the entire book. This is a surprising shortcoming in an otherwise captivating and (hopefully) effective manifesto, especially given the potential of our profession to support people with Parkinson's.

What role can psychology have in the PACT for Parkinson's? Starting with prevention, health psychology can contribute to behaviour change, in reducing risky behaviours (e.g., those leading to head trauma or the use of chemicals) and promoting protective habits (e.g., diet change, exercise). Similarly, lessons learnt from decades of mental health advocacy – often inspired by some of the infectious disease movements described in the book – could inform new ways to advocate more effectively for people with Parkinson's and their caregivers, in particular drawing from the social model of disability. 

Clinical psychology can contribute to the care of affected individuals, improving their quality of life. Psychological issues in neurodegenerative conditions have traditionally been conceptualised through the lens of neuropsychiatric frameworks. But a large body of evidence has consistently shown that non-motor difficulties like anxiety and depression are often perceived as more debilitating than motor impairments by people with Parkinson's (I co-authored the first BPS guidance on psychological approaches for Parkinson's this year, see tinyurl.com/cpc4d2pb). This is acknowledged in the book, but again without mentioning our profession. 

Treatment is intrinsically more medical in nature, but several significant psychological implications can also be considered. For instance, medication adherence currently represents a major issue in Parkinson's care, with up to 70 per cent of affected individuals not adhering partially or completely to their medication regime. While often blamed on polypharmacy – being on multiple medications – this behaviour is consistently linked to psychological difficulties, with depression representing one of its biggest predictors.

Ultimately, Ending Parkinson's Disease is an accessible, enticing, and eye-opening read on a number of crucial aspects of the condition which are often unknown or overlooked. However, if we are to steer the Parkinson's PACT ship away from the advance of this preventable pandemic, we need as many hands as possible on deck – including psychologists'.

-       Reviewed by Dr Nicolò Zarotti, Trainee Clinical Psychologist, University of East Anglia