The Parkinson’s Drug Trial: A Miracle Cure?

I’m sure many of you have seen the programme about a landmark Parkinson’s study, that was aired on the BBC last night (28^th February 2019). It is a very well-produced fly-on-the-wall documentary that follows the investigators, inventors and some participants that have pioneered a truly ‘disruptive’ trial. If you haven’t seen it, stop reading and watch now (UK readers only).

The inimitable Tom Isaacs, who was one of the first patients into the study, and who's charity the Cure Parkinson's Trust funded this study.

What made it so unique – after all, there are thousands of drug studies that take place across the UK every day. Usually a study is designed to test one thing – most often a drug. In this study, they didn’t just test if the new drug worked. They had to invent new hardware – that needed to be tested. They had to invent a new kind of brain surgery – that needed to be tested. They had to persuade fairly risk-averse regulatory bodies and ethics panels that doing all three, together, at once was fair, safe and acceptable. Regardless of the outcomes of the study, I can only marvel at the courage and dedication shown by every person involved, from the chief investigator and the whole study team, to each and every participant and their families. Medicine usually progresses by small evolution, this study was a major revolution.

So what did the study show? ***Spoiler alert*** (The second part of the documentary is due to be aired next week. Here I will review the peer-reviewed scientific data that was published in two papers this year)

The one sentence summary from the first paper might, on the surface, appear to indicate defeat, “At the 40-week point, however, we have not shown clinical benefit despite this putamen-wide tissue engagement.” However, despite the headline ‘failure’, there is so much to celebrate.

Firstly, the managed to recruit (in fact, for 42 study ‘spots’, they had over 200 people volunteer). This is no small challenge, especially when there is the very real risk of making people worse off, and asking people with Parkinson’s to travel to Bristol every month for nearly a year.

Secondly, they proved that the hardware and surgery worked, and worked safely. 

Image from BBC.com

Thirdly, and very importantly, they showed that after 40 weeks, there was no change in the dopamine-scan in those who’d had placebo; but in the GDNF group there was a marked change that took the appearances back to those expected at the early stage of Parkinson’s. Bear in mind that on average, the participants had had symptoms of Parkinson’s for over 10 years, and in some for well over 15 years!

Fourthly, at the end of 40 weeks, no patients in the placebo group had movement scores that improved by 10 or more points. However, 9 out of the 17 participants given GDNF improved by between 10 and 16 points. This was not only statistically significant (albeit as a post hoc analysis), but most definitely clinically significant.

So what else can be said? Well, firstly, there was a very strong placebo effect. At one point in the film, the mother of one of the participants says, “To have a huge operation like that, and then have to have a placebo. Is that human? Not really, is it!” The BBC have produced a very good summary on the placebo (and nocebo) effects. The fact that the placebo group did improve so much, means that there is much less of a difference between the two groups. This doesn’t necessarily mean that the GDNF didn’t work, it means that the effect is ‘lost’ in the statistical analysis. 

Furthermore, the numbers in the study were very small, with only 41 patients in total, (21 GDNF, 20 placebo.) This further reduces the chance of finding statistical differences.

A - model showing the novel equipment that was designed and made specifically for this study. B - the port that participants lived with, with which they were 'hooked up' to treatment. C - brain scan showing that the drug delivery worked exactly where it needed to. D - patient sat being infused with treatment via the 'head port'. E - A (not-so) ordinary infusion suite. (image from linked Brain paper)

After the original 40 week study, both groups continued to get another 40 weeks treatment, this time with everyone getting the GDNF. At the end of this phase, there was still no overall group differences from the very beginning to the very end between those who had 80 weeks vs 40 weeks of GDNF treatment, in terms of the movement scores off all treatment. However, those who’d had GDNF all along had fewer increases in their regular medication (to a tune of nearly 5 tablets-worth per day (59mg vs 289mg)). There was also ongoing improvement in the ability to do daily activities in those having GDNF for 80 weeks, and a continued improvement in the proportion of the day when the medication was working well.

There are several other factors that need to be borne in mind. The study cost £3m. Divided over each of the participants amounts to over £73,000 per person. Although this seems like a lot, the actual treatment cost, should this every come to clinical practice would likely be much lower, as it includes all the extra costs associated with running a complex clinical trial. Furthermore, if GDNF is ultimately shown to slow the progression of the condition, if it means that someone maintains their independence and can either carry on working (and paying tax), or stay in their own home independently, rather than take early retirement or move to a nursing home, this really is small change – and when you factor in Quality of Life benefits, must surely be a price worth paying.

Finally (and thank you for bearing with me to this point), all these patients had a diagnosis of Parkinson’s disease for around 8 years. This means that they had the pathology for approaching 20 years. Many were profoundly affected by their symptoms. To use a metaphor I’ve used previously on this blog, it is easier to blow out a match than fight a forest fire. The brain of someone with advanced Parkinson’s is vastly more effected than at the early, or even pre-symptomatic stages. Any restorative attempts are far more likely to work if you can catch it early and intervene early. This is the overwhelming conclusion from treating infections and the whole concept of cancer treatment. 

Hopefully, you and your friends will help us reach that goal with Parkinson’s. You can do your bit by helping us to identify the very earliest phase of Parkinson’s: www.predictpd.com. Taking part involves 25 minutes in front of your own computer at home, and certainly doesn’t pose any of the risks that this study did!

As a final note, I would like to say that this programme reminded me how much of a privilege it is to look after people with Parkinson’s in the clinics of the Royal Free and Luton & Dunstable Hospital; how much of a privilege it is to be at the forefront of Parkinson’s research, funded by Parkinson’s UK, and how much this motivates me while training for the London Landmarks half-marathon and Virgin Money London Marathon.

RNR