Psoriasis is a horrible disease. It can affect one's skin, which is terribly itchy, uncomfortable and burning in some case. It can also cause arthritis, which is extremely painful and can lead to major deformities. But very few people realise is that you can have psoriasis in your nails. It can cause discolouration, defomity and other horrible things.
I know this personally. I do have psoriatic arthritis after all. While I don't have skin psoriasis, I do have nail psoriasis. It is currently extremely mild, as it responded well to Methotrexate and later Enbrel. However I did struggle for years! While it was nothing like most of the pictures you would see if you Googled 'Psoriatic toe nail' (And I recommend you don't), it was very bad and painful. I had, what looked like, nails growing over my nails. It cause pain with many kinds of shoes, so I had to buy shoes based off of how much 'toe room' they gave. I ended up having to get part of one of my nails removed because it was so badly damaged.
Not only was the pain very bad, but it was extremely embarassing. I was too embarassed to wear open toe shoes, go swimming in public and all sorts of things. I can only imagine this sort of pain people with skin psoriasis go through, especially because my mum has moderate psoriasis on her legs.
It's odd how these disease are. It's as if they get you one way or another. Especially with psoriatic arthritis.