Arthritic psoriasis should be differentiated from rheumatoid arthritis, osteoarthritis, osteoporosis, and reactive arthritis. Key points of differentiation from rheumatoid arthritis: arthritic psoriasis has psoriatic lesions and is negative for rheumatoid factor. Psoriatic joint involvement is often asymmetric, while rheumatoid arthritis is often symmetric. Psoriasis often involves all the joints of a particular finger/toe, whereas this pattern of involvement is not often seen in rheumatoid arthritis. Finger (toe) inflammation is an important manifestation of arthritic psoriasis, which is not seen in rheumatoid arthritis. Inflammatory neck and back pain occurs in about half of patients with arthritic psoriasis, but it is not a manifestation of rheumatoid arthritis. The presence of both spinal and peripheral arthritis makes arthritic psoriasis very diagnostic and almost excludes rheumatoid arthritis.