Psoriatic Arthritis (PsA) is a complex, musculoskeletal disease characterized by a
heterogeneous clinical phenotype and variable disease course. With new treatment
options emerging, it has become difficult for rheumatologists to know which therapy is
best for which patient. Postponing efficacious therapy – even for six months – can result
in progression of joint erosions, decreased long-term physical function and reduced risk
of medication-free remission. Hence, there is an urgent clinical need to tailor medical
treatment to individual patients. This thesis discusses recent advances to unravel the
complexity of PsA, on a journey towards precision medicine. The clinical work presented
in this thesis provides indirect evidence for the efficacy of conventional synthetic disease
modifying anti-rheumatic drugs in PsA. The results of a literature review and experimental
laboratory research underline the importance of the adaptive immune system in disease
pathogenesis. Two new dysregulated T cell mechanisms are discovered, which could
be investigated as therapeutic targets. Furthermore, by clinical research and reviewing
literature the need for robust predictors is confirmed, both for the development of
PsA in psoriasis patients and for the response to therapy. In recent years, advancing
experimental methods, analytical techniques and computational modeling approaches
have enabled researchers to study an increasing range of clinical, (epi)genetic, immune,
and other biomarkers. Future research is warranted to discover and validate robust
prediction models to facilitate personalized treatment and prevention of PsA.