Ten patients who underwent neurosurgery at the Prince of Wales Hospital late last month have been told they may have been exposed to Creutzfeldt-Jakob Disease (CJD). The 10 were operated on with surgical instruments that may have been used to take a brain biopsy from a 53-year-old man who has since been confirmed as suffering from classic CJD. An 11th patient possibly exposed had subsequently died of other causes, the hospital said last night. Classic CJD is an incurable, deadly brain disease that causes progressive dementia and a loss of muscular control. The disease has been attributed to prions, proteins that turn normal protein molecules into deadly ones, setting off a chain reaction. Infection can take years to manifest. Classic CJD is distinct from its more notorious cousin, variant CJD, which has been linked to mad-cow disease. The CJD patient was admitted to the hospital on October 8 with deteriorating mental function and convulsions. The man's symptoms suggested encephalitis and a brain scan on October 14 also fitted that diagnosis. But his condition worsened, and on October 23 doctors performed the biopsy. The hospital said the instruments used in the surgery were cleansed according to standard procedures. Eighteen that had been in direct contact with the brain and its protective tissue were quarantined. The other patients were operated on between October 24 and November 1. The case of classic CJD was confirmed on November 4. Patrick Li Chung-ki, from Queen Elizabeth Hospital, said the incidence of classic CJD is about one case per million per year and the rate of infection in Hong Kong generally followed this pattern. He said while there had been no cases of people contracting CJD through neurosurgical instruments in the past 20 years, people who had potentially been exposed needed to be told. Existing sterilisation techniques destroyed viruses and bacteria, but were not always effective against much tougher prions. 'I don't think we can say that the risk [of exposure is zero],' Dr Li said, 'but ... it is very low.' Patients would be informed of the chances of actual infection and warned not to donate blood or organs. They would also be advised to inform doctors before undergoing future surgery so tighter infection control measures could be put in place. 'If we don't tell them then it will be difficult to implement those measures,' Dr Li said.