Background Questions on the disease course and prognosis are often among the first questions asked by the patients/parents after having received a paediatric rheumatic diagnosis. These are also important questions for the clinicians and the researchers. Paediatric rheumatology is a fairly new speciality, and through decades we have struggled to define diagnostic criteria, terminology and categorizations of many of the paediatric rheumatic diseases. Thus, today we are still lacking many of the answers regarding outcome, and especially the long-term adult outcome of these diseases.

Objectives The purpose of the lecture is to discuss the spectrum of pediatric rheumatic diseases, what kind of study design is needed to study long-term outcome, point to outcome as a multidimensional phenomenon, and try to summarize our present knowledge on long-term outcome.

Pediatric rheumatic diseases Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease of childhood. Many of the other rheumatic diseases are probably mostly the same disease as their adult counterpart, with some special phenotypic characteristics. JIA, on the contrary, has no distinct adult counterpart, and is probably of heterogeneous origin. Some of the categories are typically a disease specific for children where adult-onset are rare, while other categories may well be an early onset of the adult disease.

Outcome studies – design and challenges Historically retrospective case studies have been used to study long-term outcome. This may provide information on common and typical childhood features, but are of limited value for defining the prevalence of remission and the risk of continuous disease or flares. Prospective longitudinal cohort studies will be more informative about prognosis and outcome, but information may be hampered by selection bias of the initial cohort. Population-based prospective longitudinal cohort studies are the ideal design to study outcome in a certain disease, and especially in diseases with a varied spectrum of disease activity. Such studies are resource-demanding and depend on the ability to keep the cohort intact over time. Patient registries and databases may in the future add valuable information on long-term outcome, but selection bias will always be a challenge, and the outcome measures need to be kept simple. Even if we manage to obtain good-quality adult outcome data, outcome will always reflect “yesterday's” treatment, and thus new treatment options will necessitate new outcome studies. The prerequisite to all outcome studies is common classification criteria and common outcome measures.

Outcome is multidimensional To study outcome in rheumatic diseases, we need valid and reliable instruments to measure disease activity and remission, permanent damage, patient-reported functional disability and quality of life, and objective measurements of participation. Some of the most important advances in paediatric rheumatology research in the later years, have been the efforts of PRINTO and CARRA to develop these necessary instruments in order to facilitate future outcome studies in paediatric rheumatic diseases.

Conclusions The outcome of all the pediatric rheumatic diseases has improved a lot during the last decades in the era of modern medical treatment, especially in relation to physical disability and mortality. The biologic treatment have even changed the outcome of the most severe cases, but long-term studies are still lacking and safety of newer treatment options is a major concern, especially when treatment starts in childhood. There seem to be an agreement that most pediatric rheumatic diseases are more chronic than we tended to think. At present, a high variety in study design and definitions of outcome makes meta-analyses very difficult to perform. Accepting that only well-designed population-based prospective and very longitudinal studies can increase our still very limited knowledge of adult outcome of pediatric rheumatic diseases, we have a lot more to learn.

Disclosure of Interest None declared