There are different types of psoriatic arthritis. Classification varies, depending on the source:
- Asymmetric Oligoarticular PsA affects fewer than four joints, and (unlike RA) does not affect the same joint on both sides of the body. This type of PsA is generally considered mild due to the small number of joints affected. “Mild” is a comparative word that does not necessarily take into account the impact of the disease on a person’s life. Approximately 70% of people with psoriatic arthritis have this type.
- Symmetric Polyarticular PsA affects four or more joints, and (like RA) can affect the same joint on both sides of the body. This type of PsA is more severe since more joints are involved. Approximately 25% of people with psoriatic arthritis have this type.
- DIP Predominant affects mainly the distal interphalangeal joints of the fingers and toes. Inflammation of the DIPs is a clue that the autoimmune disease involved is PsA instead of RA. Approximately 5% of people with psoriatic arthritis have this type.
- Arthritis Mutilans, aka chronic absorptive arthritis, affects fewer than 5% of PsA and RA patients. This type is severe and causes deformity.
- Enthesitis is inflammation of the tendon/ligament insertion sites (where tendons/ligaments attach to bone). Over time, fibrosis or calcification can occur.
- Spondylitis includes inflammation of the cervical spine (neck) and sacral spine (lower back), as well as hands, feet, hips, knees, elbows, and other joints as in RA and symmetric PsA.
- Dactylitis affects fingers and toes, and indicates swelling of the entire digit. This is in contrast to RA, wherein joints will swell, but not entire fingers/toes.
ClASsification criteria for Psoriatic ARthritis (CASPAR) requires inflammatory articular disease, but not necessarily visible swelling or symmetry. Spine pain, enthesitis, or tendonitis are sufficient. If that criteria is met, then at least three points from the following five categories qualify a person for a diagnosis of psoriatic arthritis:
- Psoriasis — either
- current psoriatic skin or scalp disease diagnosed by a rheumatologist or dermatologist (2 points), or
- personal history of psoriasis (1 point), or
- 1st degree (parent, child, sibling) or 2nd degree (grandparent, grandchild, aunt, uncle, nieces, nephews, half-siblings) blood relative with psoriasis (1 point)
- Psoriatic nails (1 point)
- Negative RF blood test (1 point)
- Dactylitis (swollen “sausage” fingers/toes)– current or history (1 point)
- New bone formation near joints visible on x-ray (1 point)