Professor Pascal Richette, Dr Frank Behrens and Professor Oliver FitzGerald share their expertise on the different phenotypes of psoriatic arthritis and importance of considering all six domains of the disease.
Psoriatic arthritis is a heterogeneous disease involving up to six domains1 (see Figure 1). Every patient with psoriatic arthritis is unique: Each will present with his/her own combination of these domains, with varying severity and disease burden levels. Regardless of the individual’s combination, psoriatic arthritis has a substantial effect on patients’ lives.1
Fig. 1 The prevalence of the six domains of psoriatic arthritis2-21Tap to zoom
The chronic inflammatory state of psoriatic arthritis is a consequence of the overproduction of pro-inflammatory cytokines.22 Chronic changes to the inflammatory signalling pathways can affect cells in the joints and skin, causing symptoms of psoriatic disease, such as swelling and tenderness of the joints.22,23 Current research suggests that each domain is driven by the dysregulation of a different combination of cytokines24-42 (see Figure 2).
Fig.2 Map of cytokines by each domain24-42Tap to zoom
The clinical features of psoriatic arthritis clearly distinguish it from rheumatoid arthritis (see Figure 3).43,44 Psoriatic arthritis and rheumatoid arthritis are both autoimmune diseases characterised by pain, swelling and stiffness of the joints.43,44 However, psoriatic arthritis is usually associated with a negative serologic test for rheumatoid factor and is commonly asymmetric, presenting enthesitis and dactylitis, beyond the peripheral joint involvement (see Figure 1).45,46
Fig.3 Prominent clinical features of psoriatic arthritis and rheumatoid arthritis43, 44, 45, 47Tap to zoom
The pattern of joint involvement and bone erosion is different in psoriatic arthritis and rheumatoid arthritis.48-51 Bone changes in psoriatic arthritis include erosion and new bone formation, whereas new bone formation is not associated with rheumatoid arthritis.48-51
Psoriatic arthritis is characterised by enthesitis (inflammation of the entheses).50 Enthesitis in psoriatic arthritis is extra-articular, can have a mechanical trigger, and is associated with pain and new bone formation. On the other hand, patients with rheumatoid arthritis experience primary synovitis (see Figures 4a and 4b).50,51
Secondary synovitis may also occur with enthesitis in psoriatic arthritis. This is when synovitis occurs after the release of pro-inflammatory molecules from the entheses, and is different to the primary synovitis seen in rheumatoid arthritis.50
Fig.4a Psoriatic arthritis bone erosion50,51Tap to zoom
Fig.4b Rheumatoid arthritis bone erosion48-51Tap to zoom
In psoriatic arthritis, the radiographic progression is knowingly slower than in rheumatoid arthritis.52-58 The modified Total Sharp Score (mTSS) was created to measure joint changes in rheumatoid arthritis and has been modified to account for the clinical features of psoriatic arthritis.58 Randomised controlled trials using mTSS have been used to illustrate this difference in average progression rate (see Figure 5).52-57
Fig. 5 Radiographic progression rates in PsARCTs from 2007 to 201552-57Tap to zoom
Many patients with psoriatic arthritis have comorbid conditions59, with 42% having three or more comorbidities.60 The most frequently reported comorbidities are hypertension59, obesity59, depression1 and cardiovascular problems1.
One study of 611 patients with psoriatic arthritis identified the prevalence of the following most common comorbidities:59
Fig. 6 - Most common comorbidities of psoriatic arthritis
Patients with psoriatic arthritis are more likely to experience comorbidities than patients with psoriasis.61 In addition to this, recent studies have also shown that patients affected by psoriatic disease are more likely to have liver disease (especially non-alcoholic fatty liver disease) compared to patients with rheumatoid arthritis.62Commonly associated comorbidities of psoriatic arthritis59, 61- 63
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