Cathay's medical is very thorough. Discuss any concerns with the doctor when you do your second interview medical at Cathay City. Lying about medical history is grounds for immediate dismissal (as with most airlines), so I would recommend putting your best 'spin' on it, but not lying. If the doctor has any concerns about a specific problem, that are beyond their capacity for futher checkup, they'll request you go to a specialist (at your own cost).
Good luck and I hope it doesn't stop you getting in!