Psoriatic arthritis manifests with joint swelling and pain and can lead to permanent joint damage. There are a few patterns of joint involvement in psoriatic arthritis and in some cases it can present similarly to rheumatoid arthritis (about 15%). Spinal joint involvement (spondyloarthropathy) is common in psoriatic arthritis (about 20% people with psoriatic arthritis are affected by spondyloarthropathy).
Skin: Psoriasis is usually present in people with psoriatic arthritis but sometimes history of psoriasis or psoriasis in a first degree relative are sufficient to make a diagnosis; if other typical features are present.
Nails: Nail psoriasis is frequent in psoriatic arthritis compared to psoriasis; nail involvement also counts as a criterion when a diagnosis of psoriatic arthritis is considered. There are different kinds of nail involvement. It is important to keep in mind that nail changes are nonspecific and can be caused by other common things (like fungus and nutrient deficiencies). A dermatologist or rheumatologist can best diagnose psoriatic nail disease.
Tendons/Bones: tendons are affected in psoriatic arthritis especially at their site of insertion on bone (enthesitis). This condition can be recognized on ultrasound or MRI. When enthesitis is advanced it can lead to inflammatory reaction of the bone and new bone growth (that is different than simple spurs) at the tendon insertion site. At this stage reactive bone formation may be seen on plain X-rays.
Laboratory tests: currently, there are no antibodies to confirm a diagnosis of psoriatic arthritis. Doctors usually test for rheumatoid arthritis antibodies to rule out rheumatoid arthritis before making a diagnosis of psoriatic arthritis.