In general, there are five clinical phenotypes of psoriatic arthritis (PsA), which may occur individually or in combination. One subtype may evolve over time into a different one:
- Symmetrical polyarthritis (30-50% of cases) is likely the most common phenotype of PsA.
- Asymmetrical oligoarthritis is also a common presentation of PsA.
- Distal interphalangeal (DIP) joint involvement is virtually always associated with nail psoriasis (image below).
- Arthritis mutilans is characterized by resorption of the phalanges (image below).
- Axial arthritis may be different in character from ankylosing spondylitis, the prototypical HLA-B27-associated spondyloarthritis. It may present as inflammatory low back pain with radiographic evidence of sacroiliitis, which is usually asymmetrical and can be asymptomatic, or spondylitis, which may occur without sacroiliitis and may affect any level of the spine in a non-contiguous manner.
In addition to psoriasiform lesions, there are a number of other characteristic, though not necessarily pathognomonic, clinical features of PsA:
- Nail involvement may be manifested as onycholysis (image below),
or nail pitting (image below).
- Dactylitis presents as the so-called “sausage digit”, diffuse swelling of the entire digit likely due to a combination of both arthritis and tenosynovitis (image below).
- Enthesitis, inflammation at insertion sites of tendon to bone (images below), is a shared characteristic of the spondyloarthritis.
- Extra-articular manifestations occur infrequently, but may include ocular inflammation (e.g. conjunctivitis, episcleritis, scleritis, and iritis), oral ulcers, and urethritis.
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*Images within this article are from the American College of Rheumatology Slide Collection.