Soriasis medication banned substance for Powerlifiting?

I recently was diagnosed with a severe case of Soriasis, a skin disorder. For treatment the doctor told me the only thing that would clear it up was prednisone, which I found out later is a type of steroid (not anabolic) called a Glucocorticosteroid. My skin disorder is too severe for any topical treetment since my whole body is swelled up, so he gave me oral tablets 60mg every other day. I compete in drug free powerlifting and olympic lifting competitions. I just found out this is considered a banned substance? Why? It isn't an anabolic steriod, it has nothing to do with strength! It lowers your immune system which reduces inflamation. how could this have any increase in sport performance? from what I have read it increases your cortisone level which is catablolic, breaks down your muscle! meaning it causes you to loose muscle mass and strength!

I think the main indication relevant to sports with corticosteroids is due to their mood elevating efffect (causing euphoria) and also due to possible increased motor activity.
 
If it is a systemic application (not topical) then i think it is allowed IF:
IT can be justfied on medical grounds & a document presented to the Anti-Doping Commission
 
Saying this, im not sure if thats the way the powerlifting/weightlifting governing bodies work. Youre absolutely right, they are catabolic hormones, not anabolic.
 
From a medical point of view, thats the only possible effects that i can think of that may cause corticosteroids to be banned.