Epidemiology.

Epidemiological research in the field of paediatric rheumatology is important for reasons such as the identification of possible aetiological factors, description of the natural history, identification of biologically homogeneous disease groups and health care planning. This review will focus on the epidemiology of 'idiopathic' juvenile arthritis (JA) where data are available for comparison in terms of time, space and ethnic origin. Methodological issues that make comparisons of data difficult, such as case definition, source population and case ascertainment, will be discussed in relation to the data presented. The incidence and prevalence of JA cover a wide range, but, in studies that use similar methodology, an incidence of 5-18 and a prevalence of 30-150 per 100,000 children under the age of 16 is found in Europe and on the American continent. Studies from other parts of the world indicate differences in age of onset and subgroup distribution related to geographical location and/or race.

Epidemiology of rheumatic disease in children.

Major problems associated with interpreting and comparing epidemiologic studies on chronic arthropathies in children include the diversity of classification criteria and selection bias. A new set of classification criteria for peripheral arthritis in children, aiming toward defining biologically homogeneous subgroups, was recently proposed and should be further tested. Descriptive studies from all over the world are now emerging on childhood rheumatic diseases, increasing the potential for comparing the impact of genetic and environmental factors on disease frequency and manifestations. Awareness about pain syndromes in children, such as juvenile primary fibromyalgia and reflex sympathetic dystrophy, has increased, and this population now forms a substantial portion of clinic visits in pediatric rheumatology. The impact of the rheumatic diseases in children on disability and quality of life during childhood and in adult life is still to a large extent unknown and must be further studied in an epidemiologic context.

The natural history of juvenile chronic arthritis: a population based cohort study. I. Onset and disease process.

OBJECTIVE: To study the natural history and the disease process in a population based cohort of patients with juvenile chronic arthritis (JCA) who were in the process of being transferred from pediatric to adult rheumatology care. METHODS: From a prospective population based epidemiological study in southwestern Sweden the cohort of patients with JCA born from 1968 through 1972 were investigated after a median disease duration of 7.1 years. The study cohort constituted of 124 patients with median age 17.7 years. RESULTS: At followup 49.2% patients still required medication, 20.2% had inactive disease and 30.6% were in remission. The highest risk of continuing disease activity was observed in patients with short disease duration (RR = 9.0) or very long duration (RR = 2.5) compared with those having medium long duration. Girls were 5 times more likely than boys to have continuing disease activity. Based on incidence data from the total population of the epidemiological study it can be estimated that an additional 100 patients with JCA, who were in remission in the beginning of the study, should be included in the present cohort. Thus a total of 60% of the patients with JCA had disease in remission and 70% were rid of disease activity when reaching adulthood in a population based setting. CONCLUSION: The selection of patients in studies of the natural history of JCA markedly influences the results, which may be one explanation for the divergent views of JCA as both a mild and a progressive disease.

The natural history of juvenile chronic arthritis: a population based cohort study. II. Outcome.

OBJECTIVE: To investigate the outcome in a population based cohort of patients with juvenile chronic arthritis (JCA) who were in the process of being transferred from pediatric to adult rheumatology care. METHODS: The cohort of patients born in 1968 through 1972, recruited from a population based epidemiological study in southwestern Sweden, were called to a followup after a median disease duration of 7.1 years. The study group consisted of 124 patients with a median age of 17.7 years. The disability and discomfort dimensions were evaluated using the Childhood Health Assessment Questionnaire (C-HAQ). The impact of the disease on social life was evaluated by patients and parents. RESULTS: The median C-HAQ disability index was 0.19 with a range from 0 to 2.75 (maximum possible score = 3). Sixty percent of the patients indicated some difficulty in daily activities. Female sex and a polyarticular disease course were risk factors for disability. The strongest determinants for disability were continuing disease activity and a positive IgM rheumatoid factor. Social impact of the disease was strongly linked to a raised C-HAQ disability index. CONCLUSION: Even in a population based study of JCA, which includes many mild cases, the majority of patients experienced some difficulty in daily activities when judged by themselves. This underlines the necessity to use the patient's own values in outcome studies, rather than the physician's. Further development of internationally accepted, standardized instruments to evaluate the handicap dimension of childhood arthritis is called for.

Physical training of children with juvenile chronic arthritis. Effects on force, endurance and EMG response to localized muscle fatigue.

We examined force, endurance and the electromyographic response to muscle fatigue in ten children with juvenile chronic arthritis (JCA) and ten age-matched healthy controls before and after physical training. Our main finding was a reduced electromyographic response to localized muscle fatigue in the patient group. After training there was a tendency towards a normalized response pattern. A possible explanation may be selective type-II muscle fiber atrophy, and recovery of these fibers after training.

Epidemiology of juvenile chronic arthritis in southwestern Sweden: a 5-year prospective population study.

Previous epidemiological studies of juvenile chronic arthritis (JCA) report divergent results owing to differences in diagnostic criteria, patient retrieval, and study designs. To investigate incidence and prevalence of JCA in a total population, this prospective survey was performed in southwestern Sweden between 1984 and 1988. Cases were identified using the European League Against Rheumatism criteria for JCA and were reported annually from eight pediatric departments and local pediatricians in the studied area. During the 5 years, 213 new cases of JCA were found, corresponding to an incidence of 54.6 per 100,000 children younger than 16 years of age. The average annual incidence was 10.9 per 100,000. The peak incidence rate, 18.3 per 100,000 was found in girls 0 through 3 years old. The lowest incidence rate, 6.4 per 100,000, was found among boys 12 through 15 years old. In December 1988, 334 cases of JCA were recorded, giving a prevalence of 86.3 per 100,000. When patients in remission were omitted the prevalence was 64.1 per 100,000. The monoarticular+pauciarticular onset type constituted 68.3% of the prevalence cases, while 21.9 were polyarticular and 6.6% had systemic onset. To avoid underestimation of incidence and prevalence, and to get a correct picture of disease patterns, epidemiological surveys of JCA should be population-based rather than referral center-based. Further descriptive studies of JCA in different well-defined geographic areas are important to make valid comparisons. Such comparisons could give clues to etiological factors, both genetic and environmental.

Craniomandibular function in juvenile chronic arthritis. A clinical and radiographic study.

Craniomandibular function was studied in 70 subjects with juvenile chronic arthritis (JCA). The subjects represented the total group of children and adolescents with the diagnosis JCA in a Swedish county. At examination, the median age of the subjects was 11.9 years and the median duration of the disease was 2.6 years. The most important finding of the study was the high prevalence (41%) of radiographic signs of temporomandibular joint (TMJ) pathology. Few subjects showed the typical craniofacial abnormalities associated with JCA, like mandibular micrognathia, facial asymmetries and open bite. Subjective symptoms of dysfunction were almost absent in subjects younger than seven years but were reported by 56% of the older subjects. TMJ sounds and pain on jaw movements were the most frequent symptoms reported. At the clinical examination, TMJ crepitations and restricted horizontal jaw movements were noted in 26% and 32% respectively. The high prevalence of TMJ involvement found in this study underlines the importance that dentists become part of the medical team responsible for the treatment of children and adolescents with JCA.