Psoriatic arthritis (PsA) is a chronic inflammatory arthritis that affects 0.3–1% of the general population and from 5% to >30% of patients with psoriasis, depending on the population studied.1
The onset of PsA usually occurs from 30 to 55 years of age.1,2,3
Despite the small percentage of the general population affected, PsA has a marked effect on healthcare utilisation and the functional ability of patients. The disability and morbidity associated with PsA are substantial, and mortality is increased compared with the general population.4,5,6,7
In the US, the direct costs of caring for patients with psoriasis and PsA (including hospitalisations, doctors' visits, and drug and non‐drug treatments) may be nearly US$650 million/year.8
Assessments of direct costs do not quantify the functional impairment associated with PsA, including pain and emotional effect on quality of life (QOL) and work‐related disability. A recent study showed a statistically significantly lower rate of employment for patients with PsA and an increased relative risk for unemployment with longer disease duration.9
Previous studies that have evaluated patient‐reported outcomes, such as the generic health status measure, the Short‐Form 36 Health Survey (SF‐36) and the disease‐specific Health Assessment Questionnaire Disability Index (HAQ DI), have found that PsA reduces QOL compared with that of the general population and its effect is similar to that of patients with rheumatoid arthritis.10,11,12,13
Patients with PsA are primarily afflicted with progressive joint damage and skin‐related physical effects that can severely affect functional ability during their productive years.4,6,14,15,16
In one study, Husted et al17
estimated that 72% of patients with PsA experienced either enduring physical disability or fluctuating states of physical disability during a 10‐year period. Although peripheral joint damage may be greater in patients with rheumatoid arthritis than in PsA, degrees of functional limitations and disability are often similar.18
However, Rahman et al19
showed no difference in radiological scores between patients with rheumatoid arthritis and those with PsA. Psoriasis also causes marked physical pain and disfigurement that may contribute to the emotional and psychosocial effects of PsA.16,20
One study found that 39% of patients with PsA indicated that the disease is a huge problem in everyday life.21
Therefore, effective treatments may considerably improve the QOL of patients with PsA.
In clinical trials, tumour necrosis factor (TNF) antagonists have shown marked improvements in skin and joint manifestations of PsA, and they have been shown to markedly improve patients' QOL.22
Adalimumab (HUMIRA; Abbott, Abbott Park, Illinois, USA) is a fully human, monoclonal antibody that binds to TNF with great specificity and affinity. It has shown beneficial effects in clinical trials on the signs and symptoms and psoriatic skin lesions of PsA.22
ADEPT (Adalimumab Effectiveness in Psoriatic Arthritis Trial), a 24‐week, phase III randomised, controlled trial, was conducted to evaluate the efficacy and safety of adalimumab in patients with moderately to severely active PsA.22
Results from ADEPT showed significant responses for both 20% improvement in the American College of Rheumatology response (ACR20) and 75% improvement in the Psoriasis Area and Severity Index (PASI 75) versus placebo at 12 and 24 weeks (p<0.001 for both).22
In addition, adalimumab was associated with significant inhibition of radiographic progression versus placebo at 24 weeks (p<0.001). Adalimumab was generally well tolerated, with a similar incidence of adverse events compared with placebo.
Although clinical measures such as ACR20 or PASI 75 are important end points in clinical trials of PsA, to a patient, the primary goal of treatment is to reduce pain, increase the ability to function, reduce fatigue and improve well‐being, allowing them to carry out normal daily activities. For this reason, it is important to also assess response to treatment from a patient's perspective through the use of disease‐specific measures, as well as comprehensive generic health status measures. This paper reports on the effect of adalimumab on physical and dermatological‐related functional limitations in PsA, as well as health‐related quality of life (HRQOL), fatigue and pain, as quantified by well‐established, disease‐specific measures and generic, patient‐reported outcome measures assessed during the ADEPT trial. The clinical relevance of the established patient‐reported outcomes in PsA is also dealt with.