Logo: to the web site of Uppsala University

Juvenile idiopathic arthritis, JIA, is used as an umbrella term covering a heterogeneous group of chronic arthritis forms in children, many of which have important differences compared to adult arthritis, while others possibly represent similar diseases among children and adults. Classification aims to give a better understanding of the pathogenesis, patterns, disease trajectories and treatment responses. For the juvenile psoriatic arthritis, JPsA, the classification criteria are currently being debated. The distribution of affected joints in JIA differs greatly and it is unknown why some joints appear to be more affected than others. The temporomandibular joint (TMJ) can be affected early in the course of the disease and often the symptoms are mild and without obvious swelling.

This thesis has its origin in the Nordic Study Group of Paediatric Rheumatology and the population-based prospective study of 510 children with newly diagnosed JIA included between 1997 and 1999. Totally 440 children were included in the eight-year follow-up, and in the TMJ study 265 patients were examined and underwent cone-beam computed tomography, CBCT, 17 years after onset.

After eight years a considerable proportion of the children with definite psoriasis were classified as undifferentiated JIA based on the exclusion criteria in the ILAR classification. Our data also presents the heterogenicity of JPsA and the development over time of clinical variables supporting a psoriatic diathesis, as well as the overlap between JPsA and enthesitis-related arthritis in a group of patients.  We found that extensive symptoms and dysfunctions of the TMJ are seen in JIA 17 years after disease onset, even in patients registered with inactive disease or remission. Individuals with substantial condylar damage on CBCT were found in all JIA categories. The deeper understanding of a chronic disease over time is crucial for research initiatives to improve care as well as for clinical decisions and planning of the health care.

Our findings suggest a need for a more appropriate classification of JPsA and also that aspects of TMJ involvement should be included in the general health assessment in JIA.

Juvenile idiopathic arthritis (JIA) is an umbrella term encompassing a heterogeneous group of chronic arthritis in children. Many of these have significant differences from adult arthritis, while others possibly represent similar diseases in children and adults. Classification aims to enhance the understanding of the disease’s pathogenesis, patterns of phenotypes, disease trajectories, and treatment responses. 

Patient-reported outcome measures (PROMs) are invaluable for assessing disease burden and play an important role in co-producing optimal health care for the child with JIA.

This thesis has its origin in the Nordic JIA study, a population-based, prospective study of 510 children with newly diagnosed JIA who were included between 1997 and 1999. In the 8-year follow-up, we found that features associated with psoriasis were linked to more severe disease progression over time. A significant proportion of children with both psoriasis and arthritis were not classified as having juvenile psoriatic arthritis (JPsA). To ensure that these children receive early, personalized treatment, future classifications should include psoriasis and psoriasis-related characteristics as criteria. 

In the 18-year follow-up, we studied temporomandibular joint (TMJ) arthritis. Orofacial symptoms and dysfunctions were common, and two-thirds of participants showed condylar deformities or erosions on cone-beam computed tomography (CBCT). An interdisciplinary approach is recommended to optimize management throughout the course of the disease.

The presence of HLA-B27 was associated with an increased risk of not being in remission off medication after 18 years of disease duration in males but not in females. Uveitis in HLA-B27 positive individuals is not always symptomatic, which clinicians need to be aware of. 

The Juvenile Arthritis Multidimensional Assessment Report, JAMAR, was translated into Swedish and validated in a clinical setting. The Swedish JAMAR proved to be a reliable tool that can be used in both routine clinical practice and research. The responses from the questionnaire can also serve as a basis for discussions between patients and caregivers.

In conclusion, JIA is a complex disease requiring attention to multiple aspects. Our results highlight the need for better classification of psoriasis in JIA, the importance of careful and multidisciplinary follow-up for TMJ arthritis, and an association between HLA-B27 positivity and more severe disease. The Swedish version of JAMAR serves as a valuable complement to existing PROMs and has the potential to enhance health care for children with JIA.