A medical expert in Hong Kong says patients who recovered from Severe Acute Respiratory Syndrome may be twice as likely to suffer from a serious side-effect caused by the steroids used to treat the illness. Some recovered SARS patients have developed a degenerative bone disorder.

Hong Kong medical authorities recently revealed that a hundred patients who recovered from Severe Acute Respiratory Syndrome have developed bone weakness and 49 are suffering from a degenerative bone disorder called avascular necrosis.

Avascular necrosis is characterized by poor blood flow into bones, leading to fractures and pain in the joints. It typically affects hip joints.

Professor K.Y. Yuen of Hong Kong University says SARS patients were treated with steroids and that bone disorders are a known side-effect of steroid treatments. But, he says, some patients treated with long courses of steroids show a lower incidence of the disorder than do SARS patients.

"The use of high-dose steroids in [patients suffering from] autoimmune disease or in transplantation patients is associated with incidence of avascular hip necrosis or avascular bone necrosis in around five percent [of patients]," he says. "In the case of SARS [patients], although duration of steroids may not be as long as in the case of autoimmune diseases? it goes up beyond ten percent."

Dr. Yuen speculates that the virus that causes SARS makes bones vulnerable and high doses of steroids further weaken bones.

The doctor says there are two possible explanations for this. First, SARS patients suffering from very serious pneumonia have trouble breathing so very little oxygen enters the blood stream. Cells that generate tissue are starved of vital oxygen. Secondly, Dr. Yuen explains that many patients with a viral infection like SARS develop clotting in tiny blood vessels, further starving tissue-generating cells of vital nutrients. While steroid treatments have been linked to bone-weakening and osteoporosis in the past, Dr. Yeun says a combination of the factors probably contribute to the high incidence of avascular necrosis in SARS patients.

SARS sickened about seventeen hundred people in Hong Kong, killing more than 200 patients. Worldwide the disease struck about 8,000 people and at least 700 died.