Background MRI plays an increasingly important role in the assessment and monitoring of disease activity in juvenile idiopathic arthritis (JIA). Awareness of the incidence and distribution pattern of MRI abnormalities in JIA is a valuable tool in the daily practice of the reading radiologist and the treating clinician. Preferred locations for pathology within target joints are facilitated by knowledge on common distribution patterns of MRI abnormalities, enabling rapid differentiation between JIA abnormalities and normal variants.
Objectives To determine (1) incidence and (2) distribution pattern of soft-tissue- and osseous abnormalities upon MRI of the two of the most affected joints in JIA (i.e. the knee and wrist)
Methods MRI datasets of 166 active JIA patients (123 with knee and 43 with wrist involvement) were analyzed. Two readers evaluated presence of 4 literature-based items per joint. Common items included synovial hypertrophy (SH), bone marrow changes (BMC), and bone erosions (BE). Joint-specific features were additionally evaluated: cartilage lesions (CL) for the knee and tenosynovits (TS) for the wrist. Scoring locations in these two joints were also literature-based. Incidence of each scored item was defined separately. Involvement per location, analyzed as percentage of the total amount of affected locations, was determined.
Results SH showed the highest incidence in both the knee and wrist (56.9-65.1% of the patients). Besides BMC (34.1%), the incidence of osteochondral features was low in the knee (CL 6.5%; BE 4.9%). In contrast, the incidence of these features in the wrist were relatively high (BMC 37.2% and BE 30.2%) and TS was present in 46.5% of the patients with wrist involvement.
In order to make MRI easy, ‘top-3-location’ per feature was constituted. Below, the ‘number 1’ or most frequently affected location per feature is mentioned. In the knee these locations consisted of cruciate ligaments (25.1% in SH), medial patella (28.1% in BMC, 33.3% in CL) and lateral femur trochlea (50% in BE).
In the wrist, the radiocarpal joint (32.8% in SH), extensor-tendon-group (83.3% in TS), lunate (15.2% in BMC) and capitate/triquetrum (21.4% in BE) were mostly affected. Being the most important feature in JIA, SH in the knee showed preferred presence in the central locations, which accounted for >85% of the total affected locations. Less obvious demarcation for SH was found in the wrist. Both in the knee and wrist the three least affected locations of SH were never found to be involved without the presence of at least one of the three other most frequently affected locations.
Conclusions This study provides an overview of incidence and distribution of a well-defined spectrum of MRI abnormalities within the knee or wrist of clinically active JIA patients. SH has highest incidence in both joints. In daily practice, a top-3-location per feature suggestive for pathology is helpful in navigation through the MRI of the knee or wrist in JIA patients.
Disclosure of Interest None Declared