For Psoriasis and Associated Arthritis:
Apply topically, directly onto plaque, Tamanu oil or (Rosehip oil+Glyercin+E+RosemaryEO) or helps a lot!
Stronger treatment is to again, apply directly onto plaque, liquid micellized Vitamin A, 5000 IU in the form of "retinyl palmitate" or "vitamin A palmitate". On Amazon.com you could buy vitamin A palmitate, micellized. You might be able to find it at a health food store as well. Put a few drops directly on a small scaly spot at night and again in the morning to see if it helps. If it helps, try expanding to a bigger area.
For the arthritis and toe pain, I find avoiding ALL nightshade plants solves the problem! You'll find a lot of information about this online. Absolutely nothing with tomatoes, white potatoes, eggplant, and all peppers except black pepper. This means no paprika, no chili powder, no jalapenos, etc. Mayonnaise has paprika in it! Most processed foods have some, however slight, red or green pepper in them. I switched from tomato based sauces to Italian dressings and I mix plain yogurt with garlic powder, onion powder, cumin, salt and black pepper for a Mexican flavor.
I also don't eat any preservatives or anything artificial. Yep, I pretty much make all my own seasonings, sauces, dressings, desserts. I also try to stay alkaline. 1-2 Alfalfa capsules helps alkalize after too much grain/meat. Also, I got colitis (bleeding colon) from the Clindamycin antibiotic that didn't cure my urinary tract infection it was suppose to cure (but that's another story). I stopped eating gluten to help my colon heal and now I just continue to not eat gluten. Gluten may increase your arthritis symptoms - you'd have to eliminate it from your diet and test that out for yourself.
The disease is mystifying doctors. They think it has to do with the immune system overreacting. Getting rid of the food triggers can help immensely! There is a whole class of "anti-nutrient" foods. If you find what I am suggesting helps tame your symptoms, you may want to go even further and google "anti-nutrients".