There is some degree of controversy over how ME should be treated
Two ME patients are launching a High Court appeal against what they say is an "unfair and irrational" approach by the NHS to their condition.
The judicial review is being brought by Kevin Short, from Norwich, and London-based Douglas Fraser.
They argue the NHS was wrong to place so much emphasis on psychological rather than medical therapies.
But the National Institute for Health and Clinical Excellence said its August 2007 guidance was "robust"
The guidance issued in August 2007 related to ME and chronic fatigue syndrome, which affect over 200,000 across the country.
Experts are divided over the severity and best way to treat the conditions - and whether they are indeed two separate illnesses.
NICE recommended cognitive behavioural therapy (CBT), a form of counselling, and planned activity programme known as graded exercise therapy (GET) as front-line treatments.
But the two men will tell the High Court that such therapies can actually be harmful to people with ME in particular.
They believe there should have been more emphasis placed on drug treatments, arguing ME can lead to cardio-vascular problems and severe joint pain.
The court was packed with other ME sufferers, many of them confined to wheelchairs, as the case opened.
Barrister Jeremy Hyam, representing both men, told the court that while the claim was being brought by just two individuals, their views were shared "across the ME community".
"Literally thousands of sufferers have communicated their support for this challenge," he said.
The guidance does call for standard drugs to be used to combat some symptoms, but the campaigners said it ignored anti-viral treatments that could stem the development of problems in the first place.
Solicitor Jamie Beagent, who is representing the pair, said: "There were two key flaws in the decision.
"Firstly, the people who assessed the guidance were weighted in favour of psychological treatments and, secondly, it was irrational and unfair.
"There is little evidence that what has been recommended actually works. NICE has virtually ruled out medical intervention and that is wrong."
The two ME patients have received the backing of the ME Association with a spokesman calling the guidance "unfit for purpose".
But NICE chief executive Andrew Dillon defended the guidance, saying it was "robust" and had been designed to improve care.
"The group considered a range of complex issue in great depth taking full account of the views of patient groups and health professionals."
And he added the court case was "diverting resources away" from NICE's core work.
The hearing is expected to last two days and the guidance will remain in place until the judge gives his verdict.