Have I got PsA?

Here's a great Christmas present (a bit delayed): pain in the left knee, out of the blue on 30th December, and ongoing. My GP thinks it is psoriatic arthritis. What do you think? Some clues: – The pain started in the hip and rapidly descended to the knee, where it has been slowly getting worse. This was seriously getting me down until I started with ibuprofen gel today. – I have had psoriasis-type flakey skin behind my knees almost all year. It spread to other places, but I have driven it back, almost completely, with hydrocortisone. – I have a long history of minor psoriasis – decades, in fact. – I also get arthritic pains in the base of my thumbs, and some of my finger joints are looking a bit out of shape (although there is no psoriasis on the hands). I am on ibuprofen gel (on knee) for pain relief, and hydrocortisone to tackle the superficial psoriasis on the knee and therefore, hopefully, inside the knee. I'm 90% sure this is psoriatic arthritis. Any other suggestions welcome. Al W