The Need for Biological Outcomes for Biological Drugs in Psoriatic Arthritis

Perhaps no disease has been bedeviled more than psoriatic arthritis (PsA), with its proliferation of different clinical outcome measures. The development of these various measures to a large degree reflects both an inability to fully grasp disease pathogenic mechanisms and the difficulty in measuring them, especially in the context of the disease’s clinical heterogeneity. The absence of biological outcome measures, including an immunological or inflammation-related serum marker, makes the tomographic ability of magnetic resonance imaging (MRI) to directly measure inflammation arguably the most useful surrogate for PsA biological disease assessment. This is important because outcome measures to assess PsA are mushrooming (Figure 1). Figure 1. The use of clinical outcome measures in (A) psoriatic arthritis (PsA) compared to (B) rheumatoid arthritis (RA) over the decades28,30. There is an exponential increase in PsA outcome measures compared to RA because of the multidimensional nature of the disease, which makes it more difficult to assess adequately. The relatively more complex nature of PsA provides a challenge in developing a good tool that can measure joints, skin, nails, and entheses, resulting in the creation of multiple tools in the search for the ideal all-in-one outcome measure. Because biological drugs specifically target the immune system, MRI, with its ability to measure inflammation in different tissues, is the technique best able to measure most of the changes in PsA. The lists of outcome measures may not be exhaustive. MRI: magnetic resonance imaging; PASI: Psoriasis Area and Severity Index; MEI: Mander Enthesitis Index; SF-36: Medical Outcomes Study Short Form-36; HAQ: Health Assessment Questionnaire; BSA: body surface area; DLQI: Dermatology Life Quality Index; PsARC: Psoriatic Arthritis Response Criteria; DAPSA: Disease Activity in PsA; BASMI: Bath Ankylosing Spondylitis Metrology Index; BASFI: Bath Ankylosing Spondylitis Function Index; BASDAI: Bath Ankylosing Spondylitis Disease Activity Index; ACR: American College … Address correspondence to Dr. A.L. Tan, Leeds Institute of Rheumatic and Musculoskeletal Medicine, Chapel Allerton Hospital, Chapeltown Road, Leeds LS7 4SA, UK; E-mail: a.l.tan{at}leeds.ac.uk