I had a similar problem with my wifes pre-existing condition. I spent a lot of time emailing the EK Clinic for clarification of which drugs and what treatment would be covered before joining - which EK promptly reneged upon when I arrived.
The clinic ended up refusing to pay for external consultations - which as an EK FO you will struggle to pay for yourself. Luckily, we were able to get some medication at no cost from our home country.
The clinic rigidly enforce the 'pre-existing condition' clause and will try and associate every other condition with it in order to wriggle out of any financial commitment. My wife was rushed into hospital with an unrelated problem and the company tried to refuse to pay - even though the consultants at the hospital said it had nothing to do with her pre-existing - the company in the end did pay so that she could be released but then docked the cost from my wages later with no warning!
The medical support for families was one of the (many) factors that went towards my decision to leave.