Patient-reported outcome measures in psoriasis: assessing the assessments
Authors: A.Y. Finlay
Journal: British Journal of Dermatology (2015)

Why should any clinician care about how psoriasis is measured? In most psoriasis consultations there is little or no measurement. The reality is that clinical decisions are taken on the history, the clinical examination and the clinician's ‘gut feeling’ about what would be best. The most compelling reason for measuring psoriasis is that measurement may improve the quality and appropriateness of clinical decisions. Clinical decision taking is subject to a wide range of influences, to which the clinician may be unaware or at least unwilling to admit.1, 2 Let's bring into the broth of clinical decision making at least a minimal record of severity or of change or of life-quality impact. Maybe the Wright brothers got away without much instrumentation, but you would rush to the exit if your pilot announced she was going to fly purely on direct vision and experience (unless of course you were about to land in the Hudson River). Although dermatologists think we have insight into the patient's perspective, in reality we are not that good at understanding it. As reported in this issue of the BJD, Kitchen et al.3 have carried out a critical review of psoriasis-specific patient-reported outcome measures (PROMs), and concluded that none is ideal. Their study is a useful starting point for anyone trying to choose what PROM would be best for their clinic or research project, or indeed for anyone setting out to develop a new measure. There is a need in dermatology for identification and adoption of high-quality PROMs, meeting specified levels of validation. This has inspired the current Harmonizing Outcome Measures for Eczema initiative,4 the Cochrane Skin Group Outcomes Research Initiative5 and the International Dermatology Outcome Measures Group.6 Guidelines developed by regulatory bodies such as the U.S. Food and Drug Administration or the European Medicines Agency may also potentially influence wider adoption of higher-quality PROMs.7 One concern over this flurry of interest in the identification and adoption of the best PROMs is that these various groups may not reach the same conclusions; indeed, as their methodologies differ, this is a highly likely outcome. If this proves correct we can look forward to continuing uncertainty about which outcome measures to choose: a sort of dermatology VHS vs. Betamax struggle. So while we await these various deliberations, what PROM choices for psoriasis do we have today? There are psoriasis-specific, dermatology-specific and generic measures to choose from. New disease-specific PROMs are frequently being published; Kitchen et al.3 identified 16 for psoriasis alone. Most have been used in very few studies, and there is little evidence of any of them being used in routine clinical practice. The dermatology-specific measures used in psoriasis are the Dermatology Life Quality Index (DLQI) and Skindex. Although there have been criticisms of the DLQI, it continues to be by far the most widely used PROM in psoriasis, perhaps because of its simplicity, widely accepted patient face validity and easy score band descriptors.8 Generic PROMs that can be used across all diseases have been used in psoriasis in research studies, but again not in routine clinical work. The Short Form 36, for example, has been used to compare the impact of psoriasis with the impact of nonskin diseases, and the EuroQol-5D is increasingly being used to assess the utility of interventions to inform national debates about funding of therapies.9 Other PROMs, such as the Hospital Anxiety and Depression Scale screening tool, should probably be used much more frequently in dermatology clinical practice, given our knowledge of the high prevalence but low recognition of depression that might benefit from intervention. Then there is an entirely novel angle concerning the measurement of the wider burden of psoriasis, not mentioned by Kitchen et al.: the impact on the quality of life of partners and other family members. Techniques to measure this are not strictly ‘patient’-reported outcome measures as they are completed by those around the patient. However, again there are available disease-specific, dermatology-specific and generic measures: the Psoriasis Family Index-14 (PFI-14),10 the Family Dermatology Life Quality Index (FDLQI) and the Family Reported Outcome Measure-16 (FROM-16).11 Although the tools now exist, there is as yet little published evidence in psoriasis of the extent of this wider burden, or of the effect of intervention. The excuses for not measuring psoriasis in the clinic are gradually getting weaker. There are now free apps to help you calculate Psoriasis Area and Severity Index scores, or to measure quality of life,12 and also attempts to assess the validity of such e-delivered measures.13 However, for a PROM to become of any real use in the clinic, there should be validated ‘meaning descriptors’ for the scores. Such data were available first for the DLQI,14 and now also for Skindex and the Simplified Psoriasis Index. These descriptors are not yet available for most psoriasis-specific PROMs. Information about the minimal important clinical difference15 is also helpful for clinical interpretation. Unless required to do so by guidelines, clinicians are never going to use PROMs in the clinical setting unless the following three criteria are met: (i) completion of the forms must be quick and not require any supervision; (ii) the scores must be easily understandable; and (iii) most importantly of all, the information must be helpful to clinicians in improving the appropriateness of their clinical decision taking. Up to now, most PROMs available for psoriasis do not have evidence of meeting all three criteria. We have a huge choice of measures and Kitchen et al.'s3 review is a useful introductory guide. The adoption of various standard measures of weight took about 4000 years to settle down, from the earliest efforts of the Indus Valley Civilization to the universal acceptance (at least in science) of the metric system. Let us hope that we can be a bit speedier agreeing on the most appropriate PROMs for psoriasis. A.Y.F. is joint copyright owner of the DLQI, PFI-14, FDLQI and FROM-16. Cardiff University gains income from the use of some of these measures. The Psoriasis360 app was organized and funded by Janssen.12