'The cause is relatively unknown, but we think there are multiple factors, including genetic and environmental influences such as viruses, overexposure to the sun and passive smoking. Hormones may play a part, as can stress, which often causes the disease to flare up,' he says. The disease is usually first evident in children from newborns up until puberty. 'At this stage in life it is often difficult to deal with,' Lee says, 'especially for adolescent girls because the steroids [used to suppress the inflammation] make them gain a lot of weight.'

In severe cases, cytotoxic drugs (often used in the treatment of cancer) are also needed.

Lee says: 'When they are students they find the situation difficult because they cannot do what their friends can do - the chronic pain affects their walking ability and the drugs affect fertility.

'Most importantly, we need to make the correct diagnosis as early as possible to prevent damage because, just like a fire, it will cause more severe problems in the organs and spread. Long-term, it's a crippling disease, so patients need to take their medicine to control the inflammation. Failure to do so can lead to organ failure or death.'

Kwok-shing, 27, knows all too well what going off medication can do to someone with severe rheumatism. After being diagnosed at seven in 1990, he stopped seeing western doctors for five years in favour of alternative treatments. 'My joints were so painful I could not walk or stand. I felt helpless, so I decided to try traditional Chinese medicine, acupuncture and other various therapies. But my condition deteriorated. Most of my joints became distorted and my hip bones were destroyed,' he says.

Despite undergoing hip replacement surgery, he is now wheelchair-bound, spending most of his days surfing the internet and watching television as he is unable to hold a job.

'I'm optimistic and haven't given up hope - one day I hope there will be a form of therapy that will change the scenario and relieve the pain.'

Shing-yan's family still worry about her long-term progress. She is now 12 and Lee says she is one of the worst cases he's seen, even though her condition is stable, thanks to her family, who have followed doctors' orders to the letter, injecting high dosages of medication to control the disease. Every month she must be admitted to hospital for two days of maintenance therapy, and drugs infused into her system.

The steroids have changed her appearance, making her gain weight. 'When she first went back to school some of her classmates were frightened to play with her,' her father says. 'But now she has adjusted back into school life.'

His wife says she is regularly distressed at seeing her daughter in so much pain.

Cheuk-ying, 18, has been suffering for more than a year.

'At first I felt very fatigued and had difficulty with simple movements such as travelling on buses and combing my hair. I saw many doctors but no one diagnosed it until six months ago, when I started treatment. But the disease had taken its toll already. The process of getting the injections is very painful and I need to have them every month.'

The Hong Kong Paediatric Rheumatism Association is lobbying the government to provide a one-stop treatment centre for the disease, as most young patients are forced to visit different specialists up to four times a week.

'This results in them falling behind in school work and frequent days off for parents from their employment, which enhances the burden on the whole family,' says Lee. 'It is exhausting for young patients with serious joint pain to visit different clinics - from rheumatologists, to occupational and physiotherapists and ophthalmologists.'

Lee says the medical support in Hong Kong for paediatric rheumatism falls behind other countries that usually have treatment centres in place.