Imaging in Juvenile Idiopathic Arthritis: A Comprehensive Review

Abstract

Juvenile idiopathic arthritis (JIA) is the most common rheumatological disorder of the pediatric age group and includes all forms of arthritis that commence within 16 years of age, last for more than 6 weeks, and are of unknown cause. Its diagnosis is mainly clinical; however, imaging is essential in cases of equivocal clinical diagnosis, evaluation of disease burden, disease activity, and joint damage. Although radiographs were being used conventionally in JIA, the advent of anti-inflammatory therapies in JIA has resulted in a paradigm shift to increased utilization of ultrasonography and magnetic resonance imaging in disease evaluation, owing to greater sensitivity of the two modalities for detection of early inflammatory stages of the disease. This review discusses the role of imaging in JIA, including salient imaging findings and available scoring systems for monitoring this entity.

 

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Keywords

juvenile idiopathic arthritis - Enthesitis-related arthritis - juvenile oligoarthritis - acquired joint deformities - radiograph - magnetic resonance imaging

Introduction

Juvenile idiopathic arthritis (JIA) is the most frequent pediatric rheumatological disorder and demonstrates synovial inflammation as a key feature.[1] [2] It encompasses all forms of arthritis that commence within 16 years of age, last for more than 6 weeks, and are of unknown cause. JIA is a disease with an unpredictable clinical course, frequent relapses, chronicity, and significant disease-related morbidities.[3] [4] [5] This heterogeneous disorder includes various subtypes, namely, oligoarthritis (most common subtype, affects 1–4 joints within 6 months of onset), rheumatoid factor (RF)-positive polyarthritis (affects ≥5 joints within 6 months of onset with at least two positive RF tests 3 months apart within 6 months of disease onset), RF-negative polyarthritis (polyarthritis with a negative RF factor), systemic arthritis (≥1 joints affected with or preceded by at least 2 weeks of fever with one of the following: transitory rash/lymphadenopathy/hepatosplenomegaly/serositis), enthesitis-related arthritis (ERA), psoriatic arthritis (PsA) (arthritis or arthritis with psoriasis with at least two of following: dactylitis, nail pitting or onycholysis, or psoriasis in a first-degree relative) and undifferentiated arthritis.[1] [6] ERA is defined by the presence of either enthesitis or arthritis or both with at least two additional criteria: clinically documented sacroiliac joint tenderness or inflammatory low back pain; positive HLA-B27 antigen; male over 6 years of age at onset; acute (symptomatic) anterior uveitis; or a first-degree relative with ankylosing spondylitis/ERA/sacroiliitis with IBD/Reiter syndrome or acute anterior uveitis. The “undifferentiated” category is utilized for patients who do not fit any criteria or fit more than one category.[6]

JIA differs from rheumatoid arthritis in adults in various aspects apart from the seropositivity for rheumatoid factor (RF). Unlike RA, JIA, especially the ERA subtype, has a higher incidence of sacroiliitis, uveitis, and enthesitis. Additionally, ankylosis is more common in JIA compared with adult RA. The diagnosis of JIA is mainly clinical; however, imaging is essential in cases of an equivocal clinical diagnosis. Additionally, clinical examination is not sensitive for the evaluation of the axial joints, such as the spine and sacroiliac joints; imaging, therefore, becomes crucial in such situations.[1] [5] Other aspects where it falls short include evaluation of disease burden, disease activity, and joint damage. Monoarticular arthritis is yet another enigma where imaging can exclude closely mimicking disease entities.[4]

Imaging plays a vital role in the diagnosis and management of JIA. It assists in the evaluation of clinically equivocal cases and assesses the extent, activity, and severity of disease, cartilage, and joint damage.[1] [7] It additionally helps in monitoring response to treatment and guides the instillation of various intra-articular therapeutic agents.[1] The choice of investigation is directed by the joint under evaluation. While radiographs remain a major investigation used for the evaluation of JIA, modalities that can actively detect inflammatory changes before the onset of joint damage are increasingly assuming more importance in the diagnostic process. This shift is primarily driven by the clinical goal to suppress inflammation early so as to prevent irreversible joint damage.[8]

This review discusses the various available modalities utilized in the assessment of JIA, followed by an enumeration of the specific imaging findings. [Table 1] summarizes the available modalities for assessing the various aspects which find relevance in the evaluation of JIA.

Table 1 Imaging modalities available in the assessment of JIA

Points under consideration	Modalities available
1. Assessment of disease (diagnostic utility), excluding mimics	MRI, radiographs
2. Assessment of disease burden	MRI
3. Assessment of disease activity and prognostication	MRI, USG
4. Assessment of cartilage and joint damage	Radiographs, MRI
5. Follow-up (including prediction of relapse)	MRI, USG
6. Evaluation of niche sites (cervical spine, sacroiliac joints)	MRI
7. Image-guided interventions (biopsy, intra-articular steroid injections)	USG

Radiographs

Radiographs are often the first and most commonly performed imaging investigation; however, they lack sensitivity to the early changes of arthritis ([Fig. 1]).[5] [7] Joint changes in advanced diseases can be seen as articular surface erosions, joint space reduction, and ankylosis in late stages ([Figs. 2] and [3]).[1] [5] [7] [9]

Fig. 1 Early radiographic changes of juvenile idiopathic arthritis (JIA) in a 5-year-old male with generalized bodyache and swelling of bilateral knees. Lateral radiographs of bilateral knees demonstrate (A and B) diffuse osteopenia with distention of both knee joints (arrows, A and B) with adjacent soft tissue swelling. Frontal radiograph of bilateral wrists shows similar findings of periarticular osteopenia and soft tissue swelling (arrows, C).

Fig. 2 Advanced radiographic changes of juvenile idiopathic arthritis (JIA). Frontal knee radiograph shows enlargement of the medial femoral condyles (white arrow, A) with a widened intercondylar notch (black arrow, A). Frontal radiograph focused on the right hip (B) shows uniform joint space reduction with subchondral irregularity and sclerosis (arrows, B). Frontal radiograph of pelvis and bilateral hips (C) in another patient with JIA shows symmetrical joint space reduction in bilateral hips with numerous subchondral erosions and sclerosis (white arrows, C). Subchondral sclerosis and irregularity with asymmetric space reduction is also observed at bilateral sacroiliac joints, suggesting sacroiliitis (black arrows, C).

Fig. 3 Sequelae of JIA. Frontal pelvic radiograph shows ankylosis of bilateral sacroiliac joints (black arrows, A) with near-complete loss of joint space in bilateral hips (white arrows, A). Posteroanterior (B) and oblique (C) views of the left hand depict marked periarticular osteopenia, ankylosis at radiocarpal, intercarpal, and 2–5th carpometacarpal joints (black arrows, B and C) with subluxation at the proximal interphalangeal joint of the index finger (white oval, B).

 

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Ultrasound

The diagnostic value of ultrasound (US) in the assessment and monitoring of patients with chronic inflammatory arthritis has increased in recent times based on its higher sensitivity than clinical examination for detecting inflammatory findings in early phases.[1] [9] Easy accessibility and radiation-free nature support its use for multiple joints. It is inexpensive and does not require sedation. A real-time multi-joint assessment is possible using this modality.

In the initial course of JIA, its typical US features include synovial thickening, its hypervascularity and effusion in the joint cavity, sheath, and bursa ([Fig. 4]).[1] [9] Moreover, cartilage thinning, enthesopathies, and intra- or extra-articular fat edema can also be observed.[1] [10] Synovial inflammation that causes increased synovial perfusion and capillary permeability shows abnormally increased color and power Doppler (PD) signals.[11] [12] US has a proven role in confirming the presence of synovitis and in detecting subclinical synovitis when assessing multiple joints, especially small joints.[1] [9] [11] However, despite the efficacy of US in the detection of peripheral cartilage abnormalities, due to its low penetration, it cannot be used to evaluate axial joints. Observer variability and operator dependence are also limitations to its use.

Fig. 4 Ultrasound in evaluation of JIA. Gray scale (A) and power Doppler (B) ultrasound images of the right knee in an 8-year-old female suspected of JIA demonstrate effusion (asterisk, A and B) and irregular frond-like hypoechoic synovial thickening (arrows, A and B) showing vascularity on Doppler. Ultrasound of the left ankle (C and D) showed thickening of the tibialis anterior tendon with mild vascularity within (arrows, C and D) s/o tenosynovitis.

US finds increased utility in the treatment of JIA by permitting image-guided synovial biopsies and intra-articular instillation of various therapeutic agents such as corticosteroids. The latter in particular is safe, precise, easy to perform, can be used virtually for almost all joints and tendon sheaths with minimal complications, the major two being subcutaneous tissue atrophy and skin hypopigmentation.[13] [14]

 

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Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) assesses the inflammatory process and is more sensitive compared than physical examination, conventional radiography, or US for the evaluation of inflammatory as well as destructive changes in JIA and juvenile spondyloarthritis (JSpA).[15] MRI can assess bone marrow edema, synovial inflammation, as well as enthesopathy ([Fig. 5]). It is extremely sensitive for detecting osteochondral damage as well.[15] Lack of ionizing radiation and a superior contrast resolution are additional benefits.

Fig. 5 MRI manifestations of enthesitis-related arthropathy (ERA) in an 11-year-old male with backache and HLA B27-positive status. Coronal short-tau inversion recovery (STIR) (A), T1W (B), and postcontrast T1W fat-suppressed (C) images depict symmetrical STIR hyperintensity in bilateral hip joints (arrows, A–C) with postcontrast enhancement suggestive of synovitis and active disease. Contrast imaging is essential to differentiate synovial thickening from effusion. Coronal oblique STIR (D), T1W (E), and postcontrast (F) images focused on sacroiliac joints (SIJ) show asymmetric subchondral marrow hyperintensity and contrast enhancement at the left SIJ with predominant involvement of the iliac end (arrows, D–F), suggesting sacroiliitis. A small subchondral cyst is also appreciated at the iliac end of the left SIJ (arrowhead, D).

The application of MRI includes not only providing a diagnosis at an early stage but also determining the extent of joint involvement, monitoring disease activity, recognizing a subclinical disease, and detecting complications arising in the course of the disease, including relapse.[15] [16] [17] [18] [19] [20] Presence of synovitis on MRI, in particular, has been found to be the strongest predictor of relapse in JIA patients who are in remission.[21] Multiple MRI-based scoring systems involving the knee,[16] [17] wrist, and metacarpophalangeal joints,[15] [18] temporomandibular joints (TMJs),[19] and sacroiliac joints[20] have been developed in JIA.

While fluid-sensitive sequences such as short tau inversion recovery (STIR) and fat-saturated T2 sequences remain essential for detecting marrow edema and synovitis, contrast-enhanced MRI has been found to be superior in delineating synovitis and visualizing epiphyseal cartilage defects. Involvement of the infrapatellar knee and cruciate ligament synovial involvement in particular has been found to be specific for JIA.[22] In large joints such as the knee, MRI is helpful in the differentiation of JIA from other causes of clinically suspected noninfectious arthritis.[23] In some studies, diffusion-weighted imaging (DWI) was accurate in detecting arthritis in JIA or suspected of having JIA and showed agreement with CE-MRI.[24] [25] MRI was found to be capable of detecting cartilage microstructural changes that occur before morphological changes in an apparently intact articular cartilage.[8] [15] [26] [27]

 

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Whole-Body MRI

MRI in JIA can be performed for a particular joint or as a whole-body MRI (WBMRI). WBMRI finds immense value in the diagnosis and follow-up in JIA owing to the advantages of allowing evaluation of multiple joints in one sitting. It also helps quantify the disease in terms of number (of joints involved), screen for enthesitis and axial skeletal involvement, predict relapse, and assess response to therapy ([Figs. 6] and [7]).[21]

Fig. 6 Utility of whole body MRI in the evaluation of JIA in a 15-year-old male with left knee pain. Coronal whole body STIR images (A, B—zoomed) demonstrate hyperintense marrow alteration in bilateral tibial metaphyses (arrows, A) extending into the physis on the left side with periostitis, better appreciated on the zoomed image (arrow, B). Whole body diffusion-weighted images with inverted grayscale (DWIBS, C and D) show restriction in both lesions (white arrows, C) with additional lesions in the right ilium (black arrow, C) and right sacroiliac joint (black arrow, D). The presence of sacroiliitis assists in the differentiation of this entity from chronic recurrent multifocal osteomyelitis (CRMO).

Fig. 7 JIA in a 13-year-old male on therapy who complained of left knee pain. Serial coronal whole body STIR images (A and B) demonstrate multifocal areas of marrow edema in bilateral proximal humeral epi-metaphyses (arrows, A), left distal femoral and proximal tibial metaphyses (arrows, B). Whole body DWIBS image shows additional lesions in the right proximal and left distal tibia (arrows, C). Whole body postcontrast T1W images (E, F—zoomed image) show synovitis in the left shoulder joint (arrow, D and E). Marrow edema in the left distal metaphysis (arrow, F) was subsequently confirmed by axial STIR (G) and postcontrast images (H) with adjacent periostitis (arrows, G and H).

The increasing utilization of WBMRI in JIA mandates the development of standardized protocols which ensure optimal coverage while simultaneously reducing the acquisition time.[28] For example, post-contrast dual-echo Dixon sequences are being utilized over STIR as Dixon technique can be used in combination with contrast imaging, thereby enabling simultaneous assessment of marrow signal (on water-only sequences), structural damage (on T1-weighted in phase sequence), and synovitis (best picked up in post-contrast sequences).[29] Although the coronal plane remains the single most important plane of acquisition, certain sites of involvement merit additional imaging. For example, sacroiliac joint involvement is best assessed on coronal oblique view, sagittal view is important for spine assessment, and an axial view of the pelvis and sagittal views of knees and feet are essential to assess the entheses.[28] Additionally, involvement of TMJs requires dedicated imaging. Hence, ideally, WBMRI also needs to be tailored according to the patient's symptomatology, keeping in mind the time constraints.

At the author's institution, WBMRI is routinely used for the assessment of JIA patients. STIR, DWI, and post-contrast images are typically acquired in four to seven stations in the coronal plane (field of view: 480–480 mm, matrix: 384–269) with a total scan time of ∼45 to 50 minutes. Dedicated joint imaging is performed as per the patient's symptoms.

 

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Imaging Findings

Arthritis

Synovial inflammation and joint destruction are key features of JIA. The involvement may be restricted to a single joint, namely, monoarticular (e.g., knee), oligo or polyarticular (e.g., small joints of the hand), varying according to the subtype of JIA as detailed earlier ([Table 1]).[1] [30] [31] The various imaging features are detailed in [Table 2].

Table 2 General manifestations of JIA on imaging

Modality	Present role	Features
1. Plain radiography	● Standard imaging modality in the past; however, now the focus is shifted to detecting synovial inflammation and marrow edema, which is not possible through radiographs. ● Still utilized as a means to record the bone erosions and growth disturbances. ● Lack of definitive scoring systems (except in the wrist) due to complex changes in the growing pediatric skeleton	Early changes  ● Soft tissue swelling  ● Joint effusions  ● Periarticular or diffuse osteopenia  ● Band-like metaphyseal decreased bone density Late changes  ● Joint space narrowing (appears late after significant cartilage damage)  ● Epiphyseal overgrowth (owing to hyperemia), e.g., widening of the intercondylar notch and squaring lower pole of the patella in the knee  ● Erosive changes and subchondral cysts  ● Periostitis Sequelae (growth abnormalities)  ● Limb lengthening (in early phase due to hyperemia)  ● Limb shortening due to early physeal closure  ● Accelerated bone maturation  ● White “Harris” lines in the metaphysis of the long bones[5]  ● Bone-in-bone appearance of carpal, tarsal bones, and vertebrae[5]  ● Malalignment—flexion and extension deformities; subluxation and dislocation  ● Ankylosis
2. USG and Doppler	● More sensitive than radiography for detecting the manifestations ● Especially useful for small joints ● USG-guided procedures like intra-articular installation of steroids and biopsy	● Synovial thickening and hypervascularity  ● Effusion  ● Cartilage thinning  ● Tenosynovitis  ● Enthesopathy  ● Increased vascularity on Doppler
3. MRI (including whole body MRI)	● Early disease detection at the inflammatory phase ● Considered as the investigation of choice as per joint ESSR-ESPR guidelines[8] ● TMJ MRI could be performed in patients suspected clinically of TMJ involvement[8] ● MRI of the whole spine to be considered in JIA patients with the clinical involvement of the spine[8] ● MRI in children with suspected axial SpA can include sacroiliac joints and hips[8] [15] ● Increasing literature of whole-body MRI in evaluation[15] ● Multiple scoring systems based on MRI are available ● Potential role in prediction of relapse[21]	● Synovitis—irregular synovial thickening  ● Bone marrow edema  ● T2 hypointense frondlike pannus formation  ● Rice bodies  ● Significant enhancement, especially infrapatellar and cruciate ligament synovial involvement  ● Joint effusions  ● Cartilage defects  ● Bone erosions  ● Enthesitis  ● Tenosynovitis

Abbreviations: ESPR, European Society of Pediatric Radiology; ESSR, European Society of Musculoskeletal Radiology; SpA, spondyloarthritis.

 

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Specific Joint Involvement

Temporomandibular Joint

TMJ involvement is commonly reported in JIA, with reported prevalence rates ranging between 38 and 87%.[8] [32] [33] Appearance of significant changes preceding the clinical symptoms highlights the importance of imaging the TMJ in newly diagnosed cases of JIA and also at time points when the treatment plans are changed so as to prevent long-term cosmetic and functional deformities.[8] [15] Although conventional radiography and computed tomography (CT) detect bony erosions and condylar abnormalities, they are unable to detect soft tissue changes which appear early. Similarly, USG has limited utility in axial joint arthritis.[1] [8] MRI hence is the modality of choice for the assessment of TMJ arthritis and is advocated for all symptomatic patients, preferably with contrast.[8] Typical findings of active disease include marrow edema and enhancement, joint effusion, synovial thickening, and enhancement, while chronic changes include condylar flattening, erosions, and disk abnormalities. Both open and closed mouth views should be obtained to demonstrate disk abnormalities and abnormal condylar morphology, respectively.[8] A potential limitation that one may encounter while reading MRs of JIA is inaccurate measurement of synovial thickness due to rapid dissemination of contrast from the inflamed synovium into the joint space and close proximity to enhancing retrodiscal venous plexus.[15] Simultaneous comparison with post-contrast images with fat-suppressed T2-weighted images may assist to mitigate this issue.[8] Few scoring systems have been utilized for grading the TMJ manifestation of JIA and are briefly enumerated in [Table 3].[19] [34] [35]

Table 3 Summary of available scoring systems in JIA

Joint involved	Scoring system	Key features
Knee	MRI-based: Juvenile arthritis MRI scoring system (JAMRIS)[16] [17]	Detection and grading of 4 features (2 for early inflammatory changes and 2 for advanced structural changes)  A. Synovial hypertrophy(0–2 mm, 2–4 mm, and >4 mm)  B. Bone marrow change (none, <10% volume, 10–25%, and >25%)  C. Cartilage lesion (none, <10% area, 10–25%, and >25%)  D. Bone erosions (none, <10% volume, 10–25%, and >25%)
	USG-based-Childhood Arthritis and Rheumatology Research Alliance (CARRA) JIA USG workgroup system[45]	Recognition and grading of synovial hypertrophy, effusion, and Doppler signal in three views: Longitudinal suprapatellar view; medial, lateral parapatellar transverse views
Hip	Radiography-based: Childhood Arthritis Radiographic Score of the Hip (CARSH)[46]	Based on the grading of the following abnormalities  A. Joint space narrowing (<50%/>50%/ankylosis)  B. Erosions (small/marked/severe/extensive  C. Growth abnormalities (mild/severe)  D. Subchondral cysts (mild/severe)  E. Malalignment  F. Acetabular sclerosis  G. Avascular necrosis of the femoral head
Wrist	Radiography-based: Sharp/van der Heijde score[47]	Joint space narrowing and erosions scored in 15 and 16 areas in the hand and wrist, respectively. Total score ranges from 0 to 280.
	MRI-based: Damasio et al[18]	Assessment of synovitis in 5 wrist recesses—distal radioulnar, radiocarpal, mid carpal, 1st carpometacarpal, and 2–5th carpometacarpal joints. 3 parameters assessed:  A. Degree of synovial enhancement  B. Effusion  C. Degree of overall inflammation
TMJ	All MRI-based  1. Koos et al's classification[19]	Division into 4 subtypes, which were further graded:  A. Condylar abnormalities—flattening, erosions, osteophytes  B. Contrast uptake  C. Synovial hypertrophy  D. Marrow edema
	2. Vaid et al's classification[34]	Division into acute and chronic features with subsequent grading  A. Acute—joint effusion, synovial enhancement, synovial thickening, and bone marrow edema  B. Chronic—Pannus formation, condylar flattening, bony erosions, and disc deformity, destruction, and displacement
	3. JAMRIS-OMERACT TMJ consensus score[35]	Grading of the following criteria from 0 to 2 points  A. Inflammatory domain—marrow edema, marrow enhancement, joint effusion, joint enhancement, and synovial thickening  B. Osteochondral domain—condylar flattening, erosions, and disk abnormalities
Spine	None	None
Sacroiliac joint	All MRI-based  1. Spondyloarthritis Research Consortium of Canada (SPARCC)[20]	Cartilaginous portion of SIJ scored for the following:  A. SPARCC sacroiliac joint (SIJ) inflammation score (SIS)—BME, intensity, and depth for inflammation lesions  B. SPARCC SIJ structural score (SSS)—erosions, fat metaplasia, backfill (fat proliferation within a previous area of erosion), sclerosis, ankylosis
	2. JAMRIS-OMERACTSIJ scoring system[38] [39]	Cartilaginous SIJ divided into 4 quadrants and scored (from 0 to 4 points)  A. Active lesions: bone marrow edema (presence, intensity, and depth), osteitis, joint fluid, joint space enhancement, inflammatory erosion, capsulitis, and enthesitis   B. Structural lesions: erosions, fat metaplasia, backfill, sclerosis, ankylosis

 

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Spinal Involvement

Cervical spine involvement is seen in more than half of the patients of JIA and is common in the polyarticular, systemic onset, and ERA subtypes.[8] [15] [36] Subclinical involvement is common, similar to TMJ involvement. Contrast-enhanced MRI (CE MRI) is the most sensitive investigation to detect changes and should be combined with conventional radiography (including flexion and extension views) so as to provide combined anatomic and functional information.[15] Characteristic radiographic findings include ankylosis of the posterior elements, especially facet joints typically at C2–C3 vertebral level with reduced IVD space and narrowed vertebral body at the same level giving the characteristic “juvenile cervical vertebrae” appearance, anterior atlantoaxial subluxation, subluxation at C2 and C7 vertebrae and irregular dens erosions giving “apple core” deformity.[1] [15] [36] Atlantoaxial instability may require demonstration with flexion and extension views. Osteoporosis and loss of cervical lordosis are the other features that can be appreciated on the radiographs. MRI shows bone marrow edema, synovial thickening, and joint effusion at C1–C2 level in addition to the radiographic abnormalities ([Fig. 8]). It can also monitor late complications such as malalignment and neural compression.[8] Although thoracic and lumbar involvement is rare, it is prudent to do a whole spine screening to increase diagnostic accuracy. A definite role of US is yet to be elucidated when considering cervical spine evaluation in JIA. No endorsed scoring system is available for spinal involvement.

Fig. 8 Cervical spine involvement in JIA in a 10-year-old female. Sagittal T2W (A) and T1W (B) images demonstrate a widening of the atlantodens interval with a T2 hyperintense soft tissue (arrow, A). Marrow edema is also evident (yellow arrow head, A) with cortical irregularity (yellow arrow head, B). Serial axial postcontrast images (C and D) show homogeneous enhancing soft tissue suggestive of hypertrophied synovium filling the atlantodens interval and extending along the lateral masses of C2 (arrows, C and D).

Sacroiliitis

Sacroiliac joint (SIJ) involvement is frequently reported in the later course of enthesitis-related arthropathy (ERA) subtype of JIA and correlates with a negative outcome.[8] [15] The role of radiography and USG is limited in the evaluation and MRI remains the mainstay modality for assessment. Pertinent active imaging features include synovitis, capsulitis, bone marrow edema, and enthesitis ([Figs. 5] and [9]).[15] Erosions, sclerosis, fatty infiltration, and bony ankylosis are advanced features. Bone marrow edema is typically periarticular or subchondral in location and appears bright on STIR sequences ([Figs. 5] and [9]). Synovial thickening is, however, best determined and differentiated from joint effusion on Postcontrast T1 fat-saturated images.[8] Since enthesitis precedes SIJ involvement and frequently affects the hips, evaluation of the hips should be considered at the same time as SIJ imaging.[37] The MR-based scoring systems related to SIJ affliction are addressed in brief in [Table 3].[19] [38] [39]

Fig. 9 Sacroiliitis in a 16-year-old patient with JIA. Frontal pelvic radiograph shows sclerosis and irregularity in bilateral SI joints (arrows, A). Axial fat-suppressed T2W image (B) shows marrow hyperintensity involving the left SIJ joint, with predominant involvement of the iliac end (arrow, B), suggestive of residual activity in the left side.

 

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Enthesitis

The term “enthesis” denotes anatomic sites of attachment of tendons, ligaments, and joint capsules. Affliction of the synovio-entheseal complex, which consists of the entheses, adjacent synovium, and adipose tissue as a single unit, is a typical feature of JIA, especially in ERA and psoriatic arthritis subtypes.[1] [40] Damage to the enthesis resulting in an immune response in the synovium and adipose tissue explains the involvement of fibrocartilaginous joints like sacroiliac and TMJ in JIA.[40] Presence of enthesitis is an indication to consider biological disease-modifying agents in patients with psoriatic arthritis who do not show a response to glucocorticoid therapy.

USG and MRI are major modalities to be considered for evaluation. Radiographs may be negative at early stages due to poor soft tissue resolution; they may, however, assist in monitoring of erosive disease.[1] [41] USG provides a detailed assessment and identifies tendon thickening, changes in echogenicity, enthesophytes, bone erosions, and vascularity, including Doppler. MRI allows simultaneous detection of tendon, bone, and soft tissues; it identifies soft tissue edema, tendon thickening, and T2 hyperintensity near the attachment site detecting bone marrow edema which aids in diagnosis. Commonly involved regions include the insertion of the Achilles tendon on the posterior calcaneus, apophyses of the hip, and sacroiliac joints ([Fig. 10]).[15]

Fig. 10 Enthesitis-related arthropathy in a 14-year-old male. Coronal STIR (A), T1W (B), and postcontrast (C) images show marrow edema in the left acetabulum (arrow, A) with subchondral sclerosis (arrow, B) and postcontrast enhancement (white arrow, C). Left hip synovitis is also evident (arrowhead, C). Axial (D) and coronal STIR (E) images show marrow edema at bilateral ischial tuberosities (arrows, D) and anterior superior iliac spine with mild periostitis (arrow, B), suggesting enthesitis.

Inflammation of the functional entheses at the dorsal aspect of metacarpophalangeal joints, also known as peritenon extensor tendon inflammation (PTI) and annular pulleys along volar aspect of fingers related to flexor tendons, is a feature of psoriatic arthritis.[42]

 

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Extra-articular Findings

The various subtypes of JIA have known extra-articular manifestations. Associations with systemic arthritis include hepatosplenomegaly, lymphadenopathy, pulmonary disease, like interstitial fibrosis, and serositis, such as pericarditis.[43] Anterior uveitis is a frequent feature observed in oligoarthritis, RF-positive polyarthritis, psoriatic arthritis, and ERA. Uveitis in ERA tends to be symptomatic, sudden in onset, and more often unilateral as compared with other entities.[44] Psoriatic arthritis is additionally associated with skin lesions and dactylitis. Inflammatory bowel disease and Reiter's syndrome have been associated with ERA.[44]

 

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Scoring System for Severity Assessment

The majority of the scoring systems in JIA have been devised and validated on MRI owing to superior efficacy in demonstration of both soft tissue and osseous abnormalities. The joint-specific systems are briefly tabulated in [Table 3].[16] [17] [18] [19] [20] [35] [38] [39] [44] [45] [46] [47]

 

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Mimics and Differential Diagnoses

While the diagnosis of polyarticular JIA is straightforward owing to classical clinical and laboratory findings, monoarthritis or oligoarthritis poses a diagnostic conundrum. Pertinent differentials to be considered include tuberculosis, hemophilic arthropathy, and other synovial proliferative conditions such as pigmented villonodular synovitis (PVNS), synovial hemangioma, etc.[1] [48] Among these, tuberculosis remains a key diagnosis to be excluded in monoarthritis, particularly in endemic countries ([Fig. 11]).[49] [Table 4] enumerates the key diagnostic features differentiating the two entities.

Fig. 11 Mimics of JIA: Biopsy-proven tubercular arthritis in a 10-year-old boy. Frontal (A) and lateral (B) radiographs of the left ankle demonstrate subphyseal erosions in the distal tibia with an apparent widening of physis (arrows, A and B). Sagittal T2W MR image (C) shows effusion hyperintensity in the tibiotalar joint (arrow, C) and distal tibial physis (arrowhead, C). Postcontrast sagittal (D) and axial (E) images show subphyseal enhancement in distal tibial epi-metaphyses (asterisks, D) and synovitis with extension to surrounding soft tissues (arrows, D and E).

Table 4 Differentiating features of JIA from tubercular arthritis (presenting as monoarthritis)

Feature under consideration	JIA	TB
Clinical features	Uveitis common	Fever, cough, weight loss
Radiograph:	● Soft tissue swelling ● Joint effusions ● Periarticular or diffuse osteopenia ● Epiphyseal enlargement ● Advanced bone age	Overlapping features ● Phemister's triad: juxta-articular osteopenia/osteoporosis, peripheral osseous erosions, and gradual narrowing of joint space ● Epiphyseal enlargement is uncommon ● Periosteal reaction may be present
MRI
Bone marrow edema site	Epiphyseal, subchondral	Under the growth plate, metaphyseal, extensive
Transmetaphyseal spread	Absent	Seen
Extension of marrow edema beyond joint confines[47]	Not common	Common
Synovial thickening	Thick, irregular	Smooth, thin
Intraosseous abscess	Not seen	common
Periarticular soft tissue collection	uncommon	Common

Abbreviations: JIA, juvenile idiopathic arthritis; MRI, magnetic resonance imaging; TB, tuberculosis.

Additionally, Poncet's disease, which refers to polyarthritis due to immunological reaction to tubercular protein and is associated with features of active tuberculosis, should be differentiated from polyarticular JIA, especially in endemic regions.

Although uncommon in the pediatric age group, diffuse tenosynovial giant cell tumor (TSGCT), earlier known as PVNS, remains a close differential of JIA owing to the imaging appearance. The knee is most commonly involved and the presentation can be of localized or diffuse variety. Monoarticular diffuse TSGCT in particular may mimic JIA.[50] Radiographs show soft tissue swelling and joint effusion. Bone erosions are less severe (as compared with JIA) and indicative of advanced disease. Bone density is typically preserved and joint space narrowing is absent. US demonstrates a thickened and hypertrophied synovium with increased vascularity, similar to JIA. MRI is diagnostic and depicts synovial hypertrophy with intra-articular villous projections showing low T2 signal areas and blooming on gradient (GRE) images due to hemosiderin deposition. The latter finding helps establish a confident diagnosis of diffuse TSGCT.[50]

Hemophilic arthropathy also manifests with similar features observed in JIA on radiography, including epiphyseal enlargement, widened intercondylar notch in the knee, effusion, and bone erosions; however, joint space involvement is distinctly uncommon. MRI, if done, is diagnostic, showing low T2 signal hemosiderin deposition and blooming on GRE images.

Progressive pseudorheumatoid dysplasia, also known as progressive pseudorheumatoid arthropathy of childhood, is a rare genetic skeletal dysplasia that may mimic JIA at presentation owing to the common symptoms of stiffness and restricted movement in multiple joints.[48] [51] Characteristic findings of metaphyseal expansion of proximal phalanges of hand and feet, especially at proximal interphalangeal joints on hand radiographs and gouge-shaped anterosuperior vertebral endplate defects on spine radiographs, help in differentiating this entity from JIA ([Fig. 12]).[48] [51]

Fig. 12 Mimics of JIA: progressive pseudorheumatoid dysplasia (PPRD) in an 11-year-old male. Frontal radiograph of both hands demonstrates metaphyseal expansion in the short bones of the hand, most marked at the distal aspect of proximal phalanges (arrows) with flexion deformities at bilateral proximal interphalangeal joints (arrowheads). Distal epiphyses of the metacarpals are enlarged (asterisks). Periarticular erosions are distinctly not present, which, along with metaphyseal expansion, helps differentiate PPRD from inflammatory arthritis like JIA.

Chronic noninfectious osteomyelitis (CNO) may occasionally mimic JIA due to overlapping morphological features such as marrow edema. Both entities, however, are primarily differentiated on imaging on the basis of “epicenter” of the disease; CNO is typically centered in the metaphysis as opposed to JIA, which is a joint-centric disease and is associated with synovial abnormalities.[52]

 

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Recommendations and Guidelines on Choice of Imaging Modality

The choice of imaging modality to be utilized depends mainly on the body part being evaluated (e.g., knee vs. sacroiliac joints) and the course of the disease (inflammatory phase or advanced phase). [Table 5] summarizes the European League against Rheumatism (EULAR)-Pediatric Rheumatology European Society (PReS) task force guidelines on use of various imaging modalities in JIA,[26] while [Table 6] covers recommendations for performing radiography in JIA from the French societies for rheumatology, radiology, and pediatric rheumatology.[53]

Table 5 The EULAR-PReS guidelines for use of imaging modalities in JIA[26]

	Recommended investigation(s)
Diagnosis and assessment of disease extent	US and MRI (superior to clinical evaluation)
Excluding other diagnoses	US, MRI, conventional radiograph
Disease-related damage evaluation	Conventional radiograph
Damage evaluation at an early stage	US and MRI
TMJ and axial joint inflammation evaluation	MRI
Prognostication	CR (joint damage) US/MRI (persistent inflammation)
Monitoring disease activity	US and MRI
Guided joint injections	US
Detection of joint inflammation in clinically inactive joints	US and MRI

Abbreviations: CR, conventional radiography; JIA, juvenile idiopathic arthritis; MRI, magnetic resonance imaging; TMJ, temporomandibular joint; US, ultrasound.

Table 6 Recommendations from French societies for rheumatology, radiology, and pediatric rheumatology for performing conventional radiography in JIA[53]

Patient subset	Recommendation (whether radiography should be performed)
Monoarthritis at presentation	Yes
Oligo JIA (diagnosis)	Yes
Oligo JIA with inactive disease	No
RF-positive Poly JIA	Yes Wrist, hand, and forefoot, and other symptomatic joints, if any
New-onset RF-negative polyJIA with adverse prognostic factors[a]	Yes
Axial ERA	Yes Spine and hip
Multifocal enthesitis	No
JIA with persistent neck pain, MRI not available	Yes

Abbreviations: ERA, enthesitis-related arthritis; JIA, juvenile idiopathic arthritis; RF, rheumatoid factor.

^a Adverse prognostic factors: early wrist involvement, distal involvement, symmetric arthritis, high C-reactive protein/erythrocyte sedimentation rate, and bone erosions.

 

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Conclusion

Imaging in JIA forms a key part of the diagnostic evaluation and further management. While radiographs assist in the diagnosis of equivocal cases, they mainly detect advanced structural defects and have a limited role in facilitating early diagnosis. The advent of anti-inflammatory therapies to reduce the progression in JIA has resulted in a paradigm shift to increased utilization of USG and MRI in disease evaluation, owing to the greater sensitivity of the two modalities for the detection of early inflammatory stages of the disease. This has also contributed to the development of multiple joint-specific scoring MR-based systems which can assist in disease monitoring and follow-up.

 

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Conflict of Interest

None declared.

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Publication History

Article published online:
18 August 2025