PsA: a heterogeneous disease

PsA is a heterogeneous disease involving up to six domains (see Figure 1).1 Every person with PsA is unique: each will present with a different combination of these domains and varying degrees of severity. Regardless of the individual’s combination, PsA has a substantial effect on patients’ lives.1

Fig. 1 The prevalence of each of the six domains of PsA2

Expert opinion

Dr. Nicola Gullick discusses the importance of early diagnosis.

“The consequences of a delay in diagnosis would be that a patient may already have joint damage by the time they present, or they may have already lost quite a lot of function. So it’s not unusual for me to see a patient who’s had symptoms for perhaps two to three years, and they may have already lost their job by the time actually receive a diagnosis.”

Understanding PsA – dysregulation of cytokines

PsA is caused by the overproduction of pro-inflammatory cytokines; changes to inflammatory signalling pathways can affect cells in the skin and joints, causing symptoms of psoriatic disease, such as swelling and tenderness of the joints.3 Current research suggests that each domain is driven by the dysregulation of a different combination of cytokines (see Figure 2).

Fig. 2 Map of cytokines by each domain 4,5,6,7,8,9,10,11,12,13,14,15

Distinguishing PsA from Rheumatoid Arthritis (RA)

While there have been medical advances in this area, achieving an accurate diagnosis of PsA remains a challenge in the UK; specifically, distinguishing PsA from RA poses a particular issue.

Like PsA, RA is an autoimmune disease characterised by pain, swelling and stiffness of the joints (see Figure 3)3.

Fig. 3 Prominent clinical features of PsA and RA1,16,17

Expert opinion

Dr. Antoni Chan discusses the distinguishing features of PsA and explains its impact on the daily lives of patients.

“PsA has a very significant impact on patients’ day-to-day life. Firstly, if you think of the involvement of the joints, it could reduce their mobility and their independence. The pain can also be significant, and as a result of the inflammation that goes on, people have difficulty with their fatigue, their sleep, and their work.”

Other key indicators of PsA


PsA can be associated with a negative serologic test for rheumatoid factor and is commonly asymmetric, presenting enthesitis and dactylitis, beyond the peripheral joint involvement (see Figure 3)1, 18.


The pattern of joint involvement and bone erosion is different in RA and PsA.3, 19, 20 Bone changes in PsA include erosion and new bone formation, whereas new bone formation does not occur in people with RA3, 19, 20.

Psoriatic arthritis bone erosion

Fig. 4 PsA bone erosion19

Rheumatoid arthritis bone erosion

Fig. 5 RA bone erosion19


People with RA can experience primary synovitis, whereas PsA is characterised by enthesitis (inflammation of the entheses).19 Secondary synovitis can occur with enthesitis in PsA. This is different to the primary synovitis experienced by people with RA (see Figure 4 and Figure 5)19.


In PsA, radiographic disease progression is slower than in RA.21, 22, 23, 24, 25, 26 The Total Sharp Score (mTSS) was created to measure joint changes in RA and has now been modified to account for the clinical features of PsA.27

GRAPPA recommendations

The Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) identified the six domains of PsA and advocate a tailored treatment approach for patients, based on domain involvement.

Recommendations suggest targeting as many active disease domains as possible and considering a patient’s prior treatment history and comorbidities.


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