Overall prevalence is ~0.5% (range 0.1-1%), however, it affects up to 30% of patients with psoriasis 1. In contrast to many other arthropathies, there is no gender predilection in psoriatic arthritis.
Dermatological features of psoriasis precede arthritis in 90% 3. There is a strong association with nail involvement, particularly for DIP joint arthritis.
Both environmental and genetic factors are thought to play a role. Up to 60% are HLA-B27 positive 2.
The hallmark of PsA is the combination of erosive change with bone proliferation, in a predominantly distal distribution (e.g. interphalangeal more than metacarpophalangeal joints). The disease most commonly involves the hands, followed by feet. It can also affect sacroiliac joints and spine. Knees, elbows, ankles and shoulders are less frequently involved 2.
In the hands and feet, the pattern of distribution may be that of a symmetric polyarthropathy, or asymmetric oligoarthropathy.
Imaging findings include:
- enthesitis and marginal bone erosions; "pencil-in-cup" deformities are common, but not pathognomonic for PsA 3
- joint subluxation or interphalangeal ankylosis may be present.
- bone proliferation results in an irregular, “fuzzy” appearance to the bone around the affected joint 2
- periostitis: may appear as a periosteal layer of new bone, or as irregular thickening of the cortex itself 2
- dactylitis: which can present as a “sausage digit” which refers to soft tissue swelling of a whole digit; ultrasound examination of a sausage digit demonstrates underlying synovitis and tenosynovitis 4
- arthritis mutilans: a severe form of either PsA or rheumatoid arthritis caused by marked bony resorption and the consequent collapse of soft tissue; when this affects the hands, it can cause a phenomenon sometimes referred to as "telescoping fingers"
- ivory phalanx: classically involving the distal phalanx of the great toe
- sacroiliitis: often asymmetrical
- spondylitis: asymmetric paravertebral ossifications and relative sparing of the facet joints
General imaging differential considerations include:
- rheumatoid arthritis
- “gull wing” central erosions are present in erosive OA vs “mouse ears” peripheral bare area erosions in PsA
reactive arthritis (Reiter syndrome)
- tends to involve feet > hands
- 1. Klippel JH. Primer on the rheumatic diseases. Springer Verlag. (2008) ISBN:0387356649. Read it at Google Books - Find it at Amazon
- 2. Jacobson JA, Girish G, Jiang Y et-al. Radiographic evaluation of arthritis: inflammatory conditions. Radiology. 2008;248 (2): 378-89. doi:10.1148/radiol.2482062110 - Pubmed citation
- 3. Weissleder R, Wittenberg J, Harisinghani MG. Primer of diagnostic imaging. Mosby Inc. (2003) ISBN:0323023282. Read it at Google Books - Find it at Amazon
- 4. Olivieri I, Padula A, Scarano E et-al. Dactylitis or "sausage-shaped" digit. J. Rheumatol. 2007;34 (6): 1217-22. J. Rheumatol. (pdf) - Pubmed citation
- 5. Martel W, Stuck KJ, Dworin AM et-al. Erosive osteoarthritis and psoriatic arthritis: a radiologic comparison in the hand, wrist, and foot. AJR Am J Roentgenol. 1980;134 (1): 125-35. AJR Am J Roentgenol (abstract) - Pubmed citation
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