Imaging of the temporomandibular joint in children with juvenile idiopathic arthritis; references and novel scoring systems for active and permanent disease

Abstract

Sammendrag / Summary in Norwegian Bildediagnostikk av kjeveleddet hos barn med barneleddgikt; referansemateriale og skåringssystemer for å vurdere aktiv sykdom og permanent skade Barneleddgikt (juvenil idiopatisk artritt, JIA) er den vanligste, kroniske revmatiske sykdommen hos barn og rammer årlig ca. 15 barn per 100 000 i Norge. Sykdommen er en betydelig belastning for barnet i form av smerte og stivhet i ledd, langvarig behandling og hyppige kontroller i helsevesenet. Kjeveleddet er involvert hos en stor andel av pasientene, med smerter og ubehag, og mulig dårligere munnhelse. Bildediagnostikk er et viktig hjelpemiddel for å vurdere om kjeveleddene er affiserte, om der er pågående inflammasjon og om det er tilkommet permanent skade. Moderne bildediagnostikk som magnetkamera (MR) og cone-beam datortomografi (CBCT) er utfordrende å tolke. Det finnes også lite kunnskap om kjeveleddenes utseende hos friske barn. Derfor er det vanskelig å skille friske kjeveledd fra syke. For å lære mer om friske barns kjeveledd fikk vi lov å se på allerede utførte MRundersøkelser av 101 barn som ikke har JIA for å finne pålitelige bildefunn og målinger. Vi fikk også lov å gjennomføre MR og CBCT på barn med JIA. På 86 av barna med JIA testet vi et stort antall målinger og bildefunn for å se hvilke som var pålitelige. Vi fant ut at mange bildefunn og målinger av kjeveledd hos barn både med og uten JIA er upålitelige. Hos barn uten JIA er det vanlig å se kontrastvæske i kjeveleddet. Det er noe som man tidligere trodde bare forekom hos syke barn. På MR er syv bildefunn pålitelige nok til å brukes for å beskrive permanent skade og fire bildefunn kan brukes til å beskrive aktiv sykdom. Hos barn med JIA er ni bildefunn på CBCT pålitelige nok til å brukes for å beskrive permanent skade. Vi har sett at mange typer målinger av anatomiske strukturer i kjeveleddet er forbundne med stor usikkerhet. Basert på erfaringene fra pålitelighetstestene, anbefaler vi et eget skåringssystem for MR og et for CBCT. Systemene kan brukes til å vurdere kjeveleddet hos barn med JIA.

Summary in English Imaging of the temporomandibular joint in children with juvenile idiopathic arthritis; references and novel scoring systems for active and permanent disease Juvenile idiopathic arthritis (JIA) is the most common, chronic rheumatic disease in children. Globally, there are large variations in incidence, ranging from 1.6-23 per 100 000 children/year and prevalence from 3.8-400 per 100 000 children. The annual incidence in Norway is estimated at 15 per 100 000 children. Disease course and prognosis varies between different categories of JIA, and recent publications indicate that the temporomandibular joint (TMJ) is affected in a large proportion of children with JIA. Children diagnosed with JIA are more prone than their peers to develop orofacial pain, growth disturbances of the TMJ, and reduced quality of life. A large multicenter, prospective, observational, case-control study on JIA (The Norwegian JIA Study – Imaging, oral health, and quality of life in children with juvenile idiopathic arthritis, NorJIA) www.norjia.com was conducted from 2015 to 2020, including a large cohort of children with JIA in three regions of Norway. One of the focus areas for the NorJIA study is the evaluation of medical imaging of the temporomandibular joint (TMJ). Herein lies the aim to document normal variation of imaging findings and to develop robust image-based classification systems. Moreover, these aims are in line with the research strategy of the European Society of Paediatric Radiology (ESPR). Several publications during the last 10-15 years have shed light on the normal and pathological image features of the paediatric TMJ. The publications address findings using radiographic techniques, cone-beam computed tomography (CBCT), and magnetic resonance imaging (MRI), but thorough testing of the precision of these image features is lacking. Without proof of acceptable precision, the results from imaging studies will be associated with uncertainty. In this thesis we first aimed to establish normal standards for the development of the TMJ, based on the most robust MRI-based image features and continuous measurements. We then aimed to identify and test the precision of a wide set of MRI -based and CBCT-based image features of the TMJ in children with JIA. Subsequently, the aim was to propose a CBCT-based and MRI-based scoring system, based on the most precise imaging findings. In the first paper we used a retrospectively collected dataset including 101 head MRI examinations, of which 36 included images before and after intravenous contrast, performed for other reasons than JIA. Following thorough calibration three experienced radiologists performed consensus reading twice to determine agreement between each reading. In this cohort of children without JIA we found that continuous measurements showed wide limits of agreement, which is a statistical indication of low agreement between readers. Several of the categorical image features were also hampered with inaccuracy. We found that the anterior inclination increases by age, that condylar flattening in the coronal plane is a common finding, and that mild contrast enhancement of the joint tissue is very common in children without JIA. In paper two, we used a balanced dataset consisting of the MRI examinations of 86 of the participants in the NorJIA study. Two consultant radiologists scored the MRI dataset according to 25 different image features (twice by one of the radiologists). We found seven image features in the osteochondral domain and four in the inflammatory domain to be of acceptable precision. Several image features previously used to characterize disease of the TMJ in JIA turned out to be imprecise. In paper three, we used a balanced dataset consisting of 84 CBCT examinations, also drawn from the NorJIA study. Three consultant radiologists scored the dataset after thorough discussion, calibration and testing. One of the radiologists scored the dataset twice. As in paper one and two, essentially all continuous measurements of the TMJ turned out to be imprecise. From the categorical image features nine were deemed precise enough to be used further. Conclusion: For an MRI-based scoring system of the TMJ in JIA, we propose seven image features of the osteochondral domain and four in the inflammatory domain. For a CBCT-based scoring system in JIA, we propose a scoring system consisting of nine image features suitable for evaluation of TMJ deformity.