From Signs and symptoms:
"Pain, swelling, or stiffness in one or more joints is commonly present in psoriatic arthritis. Psoriatic arthritis is inflammatory, and affected joints are generally red or warm to the touch. Asymmetrical oligoarthritis, defined as inflammation affecting one to four joints during the first six months of disease, is present in 70% of cases."
This is the form that I have, affecting my left shoulder, right hip & right knee, joints that have been damaged over the years. I recently reduced the pain and inflammation in these joints by doubling my intake of EPA & DHA by eating two cans/day of Tesco Mackerel in spicy sauce, instead of one. Unfortunately, the improvement didn't last, so I'm back to one can/day.
Occasionally (when high temperatures make me feel ill), my hands & feet on the left side of my body swell, causing "sausage-fingers & sausage-toes". The reason why only the left side of my body's affected is because the heart pumps more to the left than to the right (according to my GP). One solution to this is to stop the heart from pumping so fast & hard when feeling ill by taking a β1 receptor antagonist (a.k.a. beta blocker) e.g. Atenolol. As I'm using Atenolol off-label, I get them on-line.
I completely suppressed my skin rashes and plaques since 2007, by supplementing with 5,000iu/day of Vitamin D3, ~3g/day of EPA & DHA from Sardines/Mackerel & ~400mg/day of Mg from ~4g/day of Epsom Salts spread out over my waking hours.
However, there's this (emphasis, mine):-
"Along with the above-noted pain and inflammation, there is extreme exhaustion that does not go away with adequate rest. The exhaustion may last for days or weeks without abatement."
I'm lucky in that the exhaustion isn't extreme, but it is significant and it coincides with high temperatures. Since I wrote this, I've lost 10kg and now feel slightly better in high temperatures. On the minus side, pub chairs are much less comfortable and Winter feels colder!