When Gaylia Ashby was diagnosed with a rare form of MS, it was devastating. She had just had a baby when she lost all sensation in her body and her legs became so weak she needed a wheelchair to get around. To compound her problems she found that, with less than 100 cases in the UK, patients with Devic's were guinea pigs for the little treatment available.

Rather than despair, Mrs Ashby, of west London, set about finding out as much as she could about the disease. Earlier this month she launched her own website to share information with fellow sufferers, and to fight for better treatment and research.

"It's a very lonely illness because you are unlikely to meet other people with it and there was little useful information about it," she said.

"Attacks can leave you unable to walk or to see and I didn't know if I would be able to see my children grow up or what might happen to me.

"I'm trying to change that. I can meet people through the site for support or to swap tips on treatment, and that makes a huge difference. It's somewhere we can meet to give each over the help we need."

Although there are a welter of personal sites on the internet, devoted to every conceivable illnesses, 38-year-old Mrs Ashby's is different in that it has direct support from NHS experts, who helped her devise a survey for the site to collect information on sufferers and symptoms.

Neurologists at the Walton Centre, Liverpool, hope to harness Mrs Ashby's skills as one of a new breed of expert patient, whose drive, and knowledge of her illness, makes her a powerful ally in the fight for better treatment.

Her site is one example of the way the web is transforming doctor-patient relationships. Dr Paul Cundy, the British Medical Association's spokesman on computing in general practice, said that the internet has lifted the burden on doctors to know everything about every possible illness because patients often use the web to research their symptoms before they go to a doctor.

Although initially wary, most GPs now encourage patients to look online and expect them to bring their own information to consultations.

"It used to be the doctor sitting on high but now they pool information with patients," said Dr Cundy. "There is so much information on the internet, doctors are fishing round with the patients. It's been a great leveller."

However, Dr Cundy warned people to carefully weigh up the information they find and never rely on only one site. Documents or research should list the authors and their credentials, and need to be verified by checking they can also be found in a journal or library.

He also warns people to check the site is updated regularly, to look for any advertising or commercial links, and to be wary of anything that criticises or disparages anyone, offers a miracle cure or an online diagnosis.

His warnings highlight the huge variations in quality of personal health websites. Many are just blog-style diaries of "my life with a chronic illness". But sociologist Michael Hardey, of Hull University and Hull York Medical School, said that even they can be a good way for people to find out how others cope with their illness.

Mr Hardey, who is writing a book on e-health, said many medical charities include sections on their sites for support groups, where patients can communicate with each other.

One charity was specifically set up to facilitate this. The Oxford-based DIPEx (Database of Individual Patient Experiences) was launched by a group of health managers, directors and doctors to help patients understand difficult health issues.

Researchers interviewed patients and put their responses on the web to show how they managed different illnesses. The resulting site is aimed at patients, family and friends, and health professionals, and covers conditions including infertility, chronic illness and skin diseases.

The internet is also empowering patients and giving them the tools to manage their own treatment, Mr Hardey said. "For example, people with unusual or difficult to diagnose conditions are making connections with health professionals in the US or elsewhere and are sometimes able to change their treatment."

This is what Mrs Ashby found when she first went online. She was in email contact with people in Norway, Australia, and the US, while she tried to find out more.

"I heard about a new drug in the US and a new test that helps identify those with an auto-immune disorder, so I'm finding out about that," she said.

"I have to try and think positive and do all I can. I'm not sure they will find a cure in my lifetime but I'm sure my husband will keep on fighting and my children will too."