Detection of subclinical enthesitis by ultrasonography in patients with psoriasis and controls.

INTRODUCTION: Psoriasis is a widespread chronic inflammatory skin disease; enthesitis is inflammation of the tendon, ligament, and joint capsule insertion, prevalent in patients with psoriatic arthritis. OBJECTIVES: The aim of study to evaluate the utility of the Madrid Sonography Enthesitis Index scoring system for accurate detection of subclinical enthesitis in patients with Psoriasis compared with healthy controls. Another objective was to assess increase in enthesis area and Psoriatic arthritis incidence, in a prospective 1-year follow-up. METHOD: Patients aged ≥18 years who were diagnosed with Psoriasis, without musculoskeletal complaints, and who did not have any clinical sign and/or symptom of enthesitis and synovitis were included in the study. The patients and healthy controls were evaluated with ultrasonography. Ultrasonography evaluation consisted of the detection of gray-scale enthesitis and power Doppler signal in the enthesis areas. The Madrid Sonography Enthesitis Index scoring system was used to quantify the extent of the sonographic enthesis abnormalities. RESULTS: The mean MASEI score, structure, thickness, erosion, and calcification were significantly higher in the Psoriasis group than in the control group. The mean MASEI score, structure, erosion, and calcification measurements were significantly higher at the last examination when compared to the first examination. The triceps was the most commonly affected tendon in both groups. CONCLUSION: Ultrasonography is an important tool for diagnosis and follow-up of subclinical enthesitis in patients with psoriasis. Regardless of disease duration and severity, patients should be screened using ultrasonography at yearly intervals.

'Double target' ultrasound monitoring of biologic therapy in psoriatic arthritis.

OBJECTIVES: We aimed to 1) evaluate by power Doppler (PD) ultrasound (US) the response to therapy of the most inflamed joint and enthesis (target sites) in psoriatic arthritis (PsA) patients starting a biologic disease-modifying anti-rheumatic drug (bDMARD); and 2) to investigate the correlation between the US response and clinical data. METHODS: Consecutive PsA patients with US synovitis and US 'active' enthesitis, starting a bDMARD, were included. The joint with the highest OMERACT-EULAR-US composite score and the enthesis with the highest PD grade (targets) were identified at baseline. The US examination and clinical assessment were performed at 0, 3 and 6 months. The response of OMERACT-EULAR-US synovitis composite score was defined as reaching a grade = 0 at follow-up examination; synovial and entheseal PD responses were defined as a PD=0 and/or a reduction of ≥2 PD grades at follow-up examination. RESULTS: Thirty patients were included. Synovitis composite score, synovial PD and entheseal PD showed significant responses at 3 and 6 months compared to baseline (p<0.01). Synovial PD responses were higher than entheseal PD responses at 3 months (71.4% vs 40.0%, p=0.01) and 6 months (77.8% vs. 46.7%, p=0.02). US synovitis responses were correlated with DAPSA (p<0.01) and MDA responses (p=0.01 for composite score, p=0.02 for PD). CONCLUSIONS: US was found sensitive for monitoring treatment response in PsA patients starting a biologic drug. Entheseal PD was less responsive than synovial PD, suggesting that enthesitis may represent a 'difficult-to-treat' domain in PsA.

DKK-1 in psoriatic arthritis: Correlation with disease activity and enthesopathy.

BACKGROUND: Psoriatic arthritis (PsA) is a complex inflammatory disease with varied clinical characteristics. A pathognomonic characteristic of PsA is enthesitis. Entheseal inflammation ultimately leads to the production of new bone (enthesophytes). Dickkopf-related protein-1 (DKK-1) is a wingless (Wnt) inhibitor that inhibits osteoblast function. OBJECTIVES: Assessment of the serum level of DKK-1 and its association with disease activity and enthesopathy in PsA patients. METHODS: This observational case-control study included 50 PsA patients and 50 healthy volunteers matched for age and gender. All participants were subjected to full medical history, clinical assessment, PSA activity using Disease Activity Index for Psoriatic Arthritis (DAPSA) score, the severity and extent of psoriasis were determined by the Psoriasis Area and Severity Index (PASI). Ultrasonographic assessment of the entheses was done in accordance with the Madrid Sonographic Enthesitis Index (MASEI). Serum level of DKK-1 and correlation with disease activity and enthesopathy in PsA patients were assessed. RESULTS: There was no significant difference between patients and controls regarding age and sex. The mean value of SPARCC index, DAPSA score and PASI score were 6.74±4.58, 33.24±15.26, and 8.35±10.93, respectively. There was significant difference between patients and controls regarding the serum levels of DKK-1 and MASEI score (p<0.0001). There was a significant positive correlation between serum DKK-1 and MASEI (r: 0.43527, p: 0.00158), MASEI inflammatory (r: 0.37958, p: 0.00655), and MASEI damage (r: 0.38384, p: 0.00593). CONCLUSIONS: Serum DKK-1 levels were elevated in PsA patients and were found to be correlated with MASEI score for enthesopathy.

The association between sonographic enthesitis with sonographic synovitis and tenosynovitis in psoriatic arthritis patients.

OBJECTIVES: To examine the association between sonographic enthesitis with sonographic synovitis and tenosynovitis in PsA patients, and the association between sonographic enthesitis and clinical characteristics. METHODS: Consecutive PsA patients that fulfilled the ClASsification criteria for Psoriatic ARthritis (CASPAR) were prospectively recruited. Each patient was evaluated by comprehensive clinical and sonographic assessment (greyscale and Doppler), the latter including 52 joints, 40 tendons and 14 entheses [according to MAdrid Sonography Enthesitis Index (MASEI) plus lateral epicondyles] performed by an experienced sonographer blinded to the clinical data. The US enthesitis score was further categorized to inflammatory (hypoechogenicity, thickening, bursitis and Doppler) and structural (enthesophytes/calcifications and erosions) subcategories. Multivariate linear regression models assessed the association between enthesitis and the selected variables. RESULTS: A total of 158 PsA patients [mean (s.d.) age 52.3 (13) years, 88 (55.7%) females] were analysed. Multivariate linear regression analyses showed a significant association between sonographic enthesitis and sonographic synovitis (ß = 0.18, P = 0.008) and between sonographic enthesitis and sonographic tenosynovitis (ß = 0.06, P = 0.02). These associations were derived from the enthesitis inflammatory subcategory of the MASEI (P < 0.05). Associations between enthesitis and synovitis were also demonstrated on the level of the elbow, knee and ankle joints (P < 0.05). In addition, sonographic enthesitis was significantly associated with older age, male sex, swollen joint count, CRP level and physical occupation. CONCLUSIONS: Sonographic enthesitis is associated with sonographic synovitis and tenosynovitis. The severity of sonographic enthesitis may represent a marker for inflammatory activity in other musculoskeletal domains.

The burden of entheseal involvement in systemic lupus erythematosus: a comparative ultrasonograghic study.

BACKGROUND: Imaging is crucial for identifying and diagnosis of the musculoskeletal (MSK) symptoms, which are one of the most typical manifestations of systemic lupus erythematosus (SLE). For the joints, tendons, and entheseal sites, ultrasonography has shown to be sensitive and accurate for the diagnosis of both inflammation and structural damage. AIM: The goal of the current investigation is to determine the prevalence and the distribution of entheseal abnormalities in SLE patients, using musculoskeletal ultrasonography (MSUS) and to assess the relationship between entheseal sonographic changes and the SLE disease activity. PATIENTS AND METHODS: One hundred sixty-eight subjects were studied (56 SLE patients, 56 psoriatic arthritis (PSA) patients, and 56 normal cases). To compare the frequency and the distribution of entheseal involvement, high-resolution MSUS was conducted to assess the entheseal sites of all patients in accordance with the Madrid Sonographic Enthesitis Index (MASEI). RESULTS: Clinical enthesitis was detected in 39.3% of the SLE patients using the Leeds Enthesitis Index compared to 71% detected via US examination, indicating a high proportion of subclinical enthesitis in our SLE patients. The most frequently affected enthesis was the distal insertion of the patellar tendon at the tibial tuberosity which was detected in 41% of SLE patients. Enthesitis was significantly more frequent in PSA patients (100%) compared to SLE patients (71.4%) (p < 0.05) and more significantly frequent in SLE patients compared to the healthy controls (19.6%). There was a significant correlation between MASI and SLEDAI scores (r = 0.250*, p = 0.048) and the total protein in 24 h (r = 0.289*, p = 0.031). In addition, there was an inverse significant correlation between MASEI and serum albumin (r = - 0.324*, p = 0.015). CONCLUSION: In SLE patients, enthesitis is frequently clinical and ultrasound-verified. The most impacted enthesis is at the insertion of the quadriceps tendon. Enthesitis presence and the rise in the MASI score can serve as indicators of the severity of the SLE disease. Key Points • The most impacted entheseal site lies at the insertion of the quadriceps tendon. • The presence and the rise in MASEI score can serve as indicators of the severity of the SLE disease.

Demonstrating the relationship of ultrasonographic parameters with disease activity and pain in lateral epicondylitis.

To evaluate the relationship of ultrasonographic evaluation parameters with pain, muscle strength and disease severity in lateral epicondylitis (LE). 64 people were included in present retrospective, cross-sectional study. Activity and rest pain was questioned with Visual Analog Scale (VAS). Also, Patient Rated Tennis Elbow Evaluation (PRTEE) and the maximum grip strength were evaluated. Hypoechoic region, neovascularity, cortical irregularity, enthesopathy and peritendinous fluid or bursitis were evaluated by ultrasonography. 48 of the patients were female and 16 were male. Mean age was 48.53 ±â€…6.12, body mass index was 27.70 ±â€…4.75. 55 (85.9%) hypoechoic region, 31 (48.4%) neovascularity, 21 (32.8%) cortical irregularity, 19 (29,7%) enthesopathy, and 18 (28.1%) peritendinous fluid or bursitis were detected by ultrasonography. When the ultrasonographic findings and clinical findings of the patients were compared, no significant difference was found between the hypoechoic region, cortical irregularity, enthesopathy and clinical findings (P > .05), while the extension grip strength was found to be significantly lower in patients with neovascularity (P = .045). In addition, patients with peritendinous fluid or bursitis, were found to be significantly lower in both flexion (P = .033) and extension (P = .023) grip strength, while PRTEE function (P = .021) subgroup and total (P = .038) scores were significantly higher. Hypoechoic region, cortical irregularities and enthesopathy were not evaluated to be associated with disease severity, pain and muscle strength. Neovascularity was found to be associated only with extension grip strength. Peritendinous fluid or bursitis was found to be associated with both flexion and extension grip strength and disease activity, but not associated with pain.

Effects of secukinumab on synovitis and enthesitis in patients with psoriatic arthritis: 52-week clinical and ultrasound results from the randomised, double-blind ULTIMATE trial with open label extension.

OBJECTIVES: In the ULTIMATE study with an open label extension, we assessed the long-term effect of secukinumab at tissue level on synovitis and enthesitis, and across all psoriatic arthritis (PsA) manifestations, using both clinical evaluations and power Doppler ultrasonography (PDUS). METHODS: This randomised, placebo-controlled, Phase 3 study (ULTIMATE) included biologic-naïve patients with PsA with active PDUS synovitis and clinical enthesitis, and inadequate response to conventional synthetic disease-modifying antirheumatic drugs. The study consisted of 3 treatment periods; in the first period (baseline to week 12) patients were randomised to receive subcutaneous secukinumab (150 mg or 300 mg according to severity of skin psoriasis) or placebo every week until week 4 and once every 4 weeks up to week 12. In the second period (weeks 12-24) all patients received open-label secukinumab with placebo patients switching to secukinumab (150 mg or 300 mg). The third period (weeks 24-52) was an extended open-label treatment period. The long-term responsiveness of the Global EULAR-OMERACT Synovitis Score (GLOESS), clinical enthesitis and global PDUS-detected enthesitis score (using two candidate definitions of activity) at patient level, together with clinical efficacy across key manifestations of PsA and safety were assessed. RESULTS: Of the 166 patients enrolled, 144 completed week 52. A significant reduction in GLOESS was demonstrated in the secukinumab group vs placebo at week 12, followed by a stable reduction of synovitis until week 52 in the secukinumab group while placebo switchers from week 12 reached a similar level of reduction at week 24 with stability thereafter. Likewise, a significant reduction in the Spondyloarthritis Research Consortium of Canada (SPARCC) enthesitis index was shown in the secukinumab group vs placebo at week 12 with sustained improvement to week 52. Global OMERACT PDUS enthesitis scores were numerically lower in secukinumab vs placebo switchers in the first two treatment periods, with some stability in the third period in both groups. Improvements in clinical responses were also observed across all key domains of PsA up to week 52 in both treatment groups with no new or unexpected safety signals. CONCLUSIONS: ULTIMATE showed consistent improvements in clinically and ultrasound-assessed synovitis and enthesitis and sustained clinical efficacy through week 52 in patients with PsA treated with secukinumab and placebo switched to secukinumab.

Advances in the Evaluation of Peripheral Enthesitis by Magnetic Resonance Imaging in Patients With Psoriatic Arthritis.

Enthesitis is a key disease manifestation in patients with psoriatic arthritis (PsA) that considerably contributes to pain, lower physical function, and reduced quality of life. Clinical assessment of enthesitis lacks sensitivity and specificity, and therefore better methods are urgently needed. Magnetic resonance imaging (MRI) allows detailed assessment of the components of enthesitis, and consensus-based validated MRI scoring systems exist. These include the Outcome Measures in Rheumatology (OMERACT) Heel Enthesitis MRI Scoring System (HEMRIS) method, which assesses the entheses of the heel region in a detailed manner, and the OMERACT MRI Whole-Body Score for Inflammation in Peripheral Joints and Entheses (MRI-WIPE) method, which provides an overall assessment of the inflammatory burden in the peripheral entheses and joints in the entire body using whole-body MRI. At an MRI workshop at the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) 2022 meeting in Brooklyn, the MRI appearances of peripheral enthesitis were described, as were the scoring methods. The utility of MRI for improved assessment of enthesitis was demonstrated with examples of patient cases. Clinical trials in PsA that evaluate enthesitis by MRI as a key endpoint should include the presence of MRI enthesitis as an inclusion criterion, and apply validated MRI outcomes to assess the effect of therapeutics on enthesitis are recommended.

Mineral tessellation in mouse enthesis fibrocartilage, Achilles tendon, and Hyp calcifying enthesopathy: A shared 3D mineralization pattern.

The hallmark of enthesis architecture is the 3D compositional and structural gradient encompassing four tissue zones - tendon/ligament, uncalcified fibrocartilage, calcified fibrocartilage and bone. This functional gradient accommodates the large stiffness differential between calcified bone and uncalcified tendon/ligament. Here we analyze in 3D the organization of the mouse Achilles enthesis and mineralizing Achilles tendon in comparison to lamellar bone. We use correlative, multiscale high-resolution volume imaging methods including µCT with submicrometer resolution and FIB-SEM tomography (both with deep learning-based image segmentation), and TEM and SEM imaging, to describe ultrastructural features of physiologic, age-related and aberrant mineral patterning. We applied these approaches to murine wildtype (WT) Achilles enthesis tissues to describe in normal calcifying fibrocartilage a crossfibrillar mineral tessellation pattern similar to that observed in lamellar bone, but with greater variance in mineral tesselle morphology and size. We also examined Achilles enthesis structure in Hyp mice, a murine model for the inherited osteomalacic disease X-linked hypophosphatemia (XLH) with calcifying enthesopathy. In Achilles enthesis fibrocartilage of Hyp mice, we show defective crossfibrillar mineral tessellation similar to that which occurs in Hyp lamellar bone. At the cellular level in fibrocartilage, unlike in bone where enlarged osteocyte mineral lacunae are found as peri-osteocytic lesions, mineral lacunar volumes for fibrochondrocytes did not differ between WT and Hyp mice. While both WT and Hyp aged mice demonstrate Achilles tendon midsubstance ectopic mineralization, a consistently defective mineralization pattern was observed in Hyp mice. Strong immunostaining for osteopontin was observed at all mineralization sites examined in both WT and Hyp mice. Taken together, this new 3D ultrastructural information describes details of common mineralization trajectories for enthesis, tendon and bone, which in Hyp/XLH are defective.

The use of ultrasound to detect enthesitis as a potential guide for intervention in patients with psoriasis at risk of psoriatic arthritis: a systematic review.

INTRODUCTION: Psoriatic arthritis is estimated to develop in 2% of patients with psoriasis per year and can result in significant morbidity. Early diagnosis and treatment of psoriatic arthritis are imperative to prevent irreversible arthritic joint damage. Dermatologists play a key role in identifying patients who are at risk for or with early signs of psoriatic arthritis. Subclinical enthesopathy may be a risk factor for psoriatic arthritis or an early sign of the disease and can be detected using ultrasound. METHODS: In this systematic review, we determined the prevalence of ultrasound-diagnosed enthesitis in psoriasis patients, as well as their risk of subsequent progression to psoriatic arthritis. RESULTS: We determined that the detection of enthesitis on ultrasound was associated with higher risk of future psoriatic arthritis. Systemic therapy was associated with improvement in enthesitis findings in patients with psoriasis but not in those with chronic structural damage or established psoriatic arthritis. Additionally, one study showed that ustekinumab treatment resulted in a significantly lower rate of psoriatic arthritis development. CONCLUSIONS: These studies support the value of early detection and treatment in the prevention of progression to psoriatic arthritis, as well as the use of ultrasound for screening for risk factors in psoriasis patients. Future studies are needed to further evaluate when preventative therapy can be useful among patients with psoriasis with risk factors for psoriatic arthritis.

Prevalence and clinical associations of ultrasound-confirmed enthesitis in systemic lupus erythematosus.

OBJECTIVES: To assess the prevalence of US-confirmed enthesitis in a cohort of patients with SLE and to analyse the clinical associations to enthesitis during the course of SLE. METHODS: In a retrospective analysis of the SLE cohort of the Lupus Unit of the Careggi University Hospital, US examinations of SLE patients presenting with tender and/or swollen joints were retrieved to assess the presence of enthesitis. Patients with US-proven enthesitis were compared with SLE controls with tender and/or swollen joints who showed no US evidence of enthesitis. Clinical and laboratory features were compared at disease onset and during follow-up. RESULTS: A total of 400 patients fulfilling EULAR/ACR classification criteria for SLE were assessed. Of these, 106 underwent articular US examination. Evidence of enthesitis was found in 31/106 (29.2%) patients. Seventy-one patients without US-enthesitis were included as controls; four were excluded due to lack of follow-up data. Laboratory and clinical features were comparable between cases and controls at disease onset. Throughout a median follow-up of 10.0 (interquartile range [IQR] 8.3-23.3) years for cases and 12.4 (IQR 7.2-13.3) years for controls, patients with enthesitis were less likely to develop renal involvement (22.6% vs 46.5%, P = 0.028) and failed B cell depletion more frequently (75.0% vs 0%). CONCLUSION: In SLE patients with clinically active joints, US-proven enthesitis is a fairly common finding. Enthesitis in SLE could be the hallmark of a distinct disease phenotype with less renal involvement, more arthritis and low response to anti-CD 20 therapy, potentially requiring a tailored treatment.

Validity of ultrasonography in detecting enthesitis in children: A systematic literature review.

OBJECTIVE: A systematic review to assess the value of ultrasonography (US) for detecting enthesitis in juvenile idiopathic arthritis (JIA). METHODS: PubMed and Embase databases were searched for articles published from January 1966 to May 2021; we selected those meeting the inclusion criteria according to the US definition of enthesitis and metric properties studied. We assessed the clinical features of the population, study design, the type and number of entheses examined, the definition and scoring system of US enthesitis and metric properties according to the OMERACT filter (truth, discrimination and feasibility). The quality of the studies was evaluated with the Quality Assessment of Diagnostic Accuracy Studies 2. RESULTS: Five publications met the inclusion criteria (26 to 146 patients and 1 to 10 bilaterally examined entheses). All studies focused on lower-limb entheses. The elementary lesions included in the definition of adult enthesitis were generally assessed. Few studies reported US reliability and none evaluated sensitivity to change of US. US revealed entheseal abnormalities in 9.4 to 53% of JIA patients and 20 to 83% of enthesitis-related arthritis cases. No significant abnormalities were found in healthy children. US findings were poorly correlated with clinical examination. The overall quality of the studies was low, mainly because of the lack of a reference standard. CONCLUSION: US is a sensitive tool to detect entheseal abnormalities in JIA. The current evidence highlights that a standardized US definition of enthesitis in children is lacking and US criteria and discriminant validity have not been established.

The identification of association between ultrasonographic enthesitis and the ASAS Health Index in patients with axial spondyloarthritis.

This study aimed to evaluate association between the entheseal abnormalities in ultrasound and the Assessment of Spondyloarthritis International Society Health Index (ASAS HI) in patients with axial spondyloarthritis (axSpA). Seventy-four patients with axSpA were enrolled in this study. Ultrasonographic evaluation of entheses was performed by a blinded rheumatologist with the Madrid Sonographic Enthesitis Index (MASEI). The MASEI total score and the MASEI sub-scores (e.g., structural damage and activity scores) were calculated. The ASAS HI and the other SpA tools (e.g., Bath Ankylosing Spondylitis Disease Index, the Ankylosing Spondylitis Disease Activity Score) were used to evaluate patients' health and disease activity. Correlation and multivariate linear regression analyses were performed to assess the relationship between the MASEI and the ASAS HI. The mean score of the ASAS HI was 7.7 ± 4.6. The MASEI total score was calculated as 8.4 ± 6.8, while the mean MASEI-activity was 4.7 ± 3.6 and the mean MASEI-structural damage was 3.8 ± 4.5. There was no correlation between ASAS HI and MASEI total scores (r = 0.11, p = 0.34). However, the ASAS HI had a positive correlation with the MASEI-activity (r = 0.49, p < 0.001) and had a low negative correlation with the MASEI-structural damage (r = - 0.29, p < 0.05). In the linear regression model, the MASEI-activity and MASEI-structural damage were significantly related to the ASAS HI (ß = 0.72 and - 0.58, respectively; R2 = 0.53 p < 0.001). This study reported that the ASAS HI score was more negatively affected by active entheseal lesions rather than structural lesions. We suggest adding the entheses evaluation with ultrasonography to other tools for monitoring the health status of patients with axSpA.

Efficacy of secukinumab on dactylitis in patients with active psoriatic arthritis from the FUTURE 5 study.

OBJECTIVES: Dactylitis is an important clinical domain of psoriatic arthritis (PsA) associated with significant burden of disease and impaired function. Post-hoc analysis of the FUTURE 5 study was performed to evaluate the efficacy of secukinumab in patients with dactylitis at baseline over 2 years. METHODS: Randomised patients received secukinumab 300mg with loading dose (LD)/150mg LD/150mg without loading dose/placebo. Assessment of dactylitis was based on Leeds Dactylitis Index. Exploratory analyses included resolution of dactylitis based on severity, time to first resolution of dactylitis (Kaplan-Meier estimate) and resolution of dactylitis (heatmap analysis). Clinical efficacy outcomes, composite domains of disease activity, health-related quality of life (HRQoL) and radiographic progression using van der Heijde-modified total Sharp score were assessed in patients with/without dactylitis at baseline. RESULTS: Overall, 389/996 (39%) patients presented with dactylitis at baseline, had more active clinical disease and greater disease activity than those without dactylitis at baseline. Resolution of dactylitis was observed across all treatment groups at Week 104. Improvement in joints, enthesitis, skin psoriasis, nail outcomes, physical function and HRQoL were sustained over 2 years in patients with dactylitis at baseline. With secukinumab treatment, >80% of patients did not show structural radiographic progression. The proportion of non-structural radiographic progressors were comparable across patients with/without dactylitis at baseline with secukinumab treatment over 2 years. CONCLUSIONS: Patients with dactylitis at baseline were associated with higher burden of disease. Secukinumab provided sustained improvements across all clinical outcomes, QoL and inhibition of radiographic progression in PsA patients with dactylitis at baseline over 2 years.

Non-invasive metabolic profiling of inflammation in joints and entheses by multispectral optoacoustic tomography.

OBJECTIVE: To explore the metabolic characteristics of arthritis and enthesitis using multispectral opto-acoustic tomography (MSOT), a technology using near-infrared multispectral laser to stimulate tissues and detect the emitted acoustic energy, enabling non-invasive quantification of tissue components in vivo based on differential absorbance at multiple wavelengths. METHODS: We performed a cross-sectional study in patients with RA or PsA and healthy controls (HCs). Participants underwent clinical, ultrasonographic and MSOT examination of MCP and wrist joints as well as the entheses of the common extensor tendon at the lateral humeral epicondyles and of the patellar, quadriceps and Achilles tendon. MSOT-measured haemoglobin (Hb), oxygen saturation, collagen and lipid levels were quantified and scaled mean differences between affected and unaffected joints and entheses were calculated as defined by clinical examination or ultrasonography using linear mixed effects models. RESULTS: We obtained 1535 MSOT and 982 ultrasonography scans from 87 participants (34 PsA, 17 RA, 36 HCs). Entheseal tenderness was not associated with significant metabolic changes, whereas enthesitis-related sonographic changes were associated with increased total Hb, oxygen saturation and collagen content. In contrast, the presence of arthritis-related clinical and sonographic findings showed increased Hb levels, reduced oxygen saturation and reduced collagen content. Synovial hypertrophy was associated with increased lipid content in the joints. CONCLUSION: MSOT allows determination of distinct metabolic differences between arthritis and enthesitis in a non-invasive setting in humans in vivo.