I have a close friend who has very, very severe Psoriasis that affects (and will probably shorten) her whole life. She has one of the worst cases her doctors have ever seen.
She takes Enbrel, and it has made a very significant difference for her. She isn't "cured" (I don't believe there is a cure), but her skin and her symptoms are much more manageable when she takes the Enbrel, and her life is much closer to normal. It is dangerous, and very expensive, and a real hassle, but if your condition is for SURE psoriasis, and none of the less dangerous drugs have worked, it is absolutely worth a try.