The Government is spending more than £700,000 reassessing people with the most severe cases of Parkinson's for disability benefits, even though they will never get any better, campaigners have claimed.
Charity Parkinson's UK said the figures showed the assessments process for Personal Independence Payment (PIP) "is rigging the game against people with Parkinson's".
Figures uncovered by the charity show 8,690 people with Parkinson's are claiming the highest rate of at least one element of PIP, which is awarded to those with the most severe conditions.
However, of these just 54% have been given to indefinite awards, with the rest having to undergo reassessments to keep claiming PIP.
The Department for Work and Pensions says more people with Parkinson's now get the highest level of support and assessments help ensure claimants get the right support.
Phil Reynolds, campaigns adviser at Parkinson's UK, said: "We've been warning for years that the PIP assessment is a gamble for people with Parkinson's and these figures prove it.
"Even though they have a condition that will only get worse and have qualified for the highest level of support under PIP, the DWP is adding insult to injury by forcing around half of people with Parkinson's to face stressful and unnecessary reassessments."
The figures, uncovered through a written parliamentary question, show that around a third of people with Parkinson's who have enhanced rate awards have to undergo reassessments every one to three years.
This is despite the fact Parkinson's is a degenerative condition and they will not be able to score any higher than their current award.
The National Audit Office in 2014 found a reassessment costs the DWP £182 in admin costs.
This means it will cost the DWP £728,000 to reassess everyone with Parkinson's that's been given a finite award in at least one category, according to the charity's analysis.
"With a quarter of people with Parkinson's losing some or all of the support they've had for years, and now half being denied permanent awards, it's clear PIP is rigging the game against people with Parkinson's," Mr Reynolds said.
"The Government needs to get a grip on PIP by making the assessment fit for purpose and investigating why people with worsening conditions are being hauled in for pointless reassessments time and again."
4,000 finite awards
2,670 reassessed every one to three years
Two years ago, the NAO found that the Government was spending more money assessing whether people are fit to work than it is saving in reductions to the benefits bill.
Some 70% of people with Parkinson's who were previously on Disability Living Allowance are now receiving the highest rates of PIP, compared to 40% when PIP was introduced.
A DWP spokeswoman said: "We're absolutely committed to ensuring that disabled people, including those with Parkinson's, get the support they're entitled to.
"Assessments ensure that people get the right level of support as their condition changes, including those with degenerative conditions who could miss out on getting more support if they aren't reassessed.
"Over half of claimants with Parkinson's are now getting the highest level of support under PIP - much more than under DLA.
"But we know there's more to do, and we're currently working with organisations such as Parkinson's UK to ensure that PIP supports those with severe conditions in the best possible way."