POS0153 MRI SPINAL LESIONS IN PATIENTS WITHOUT MRI OR RADIOGRAPHIC LESIONS IN THE SACROILIAC JOINTS TYPICAL OF AXIAL SPONDYLOARTHRITIS

Background

There are limited data as to the frequency of spinal lesions on MRI in patients without MRI or radiographic features typical of sacroiliac joint (SIJ) disease and to what degree spine MRI might enhance diagnostic evaluation.

Objectives

To assess the frequency of MRI lesions of the spine in the ASAS-Classification Cohort according to the presence of MRI SIJ lesions typical of axSpA and/or radiographic sacroiliitis (mNY+).

Methods

MRI spine lesions were recorded by 9 central readers in an eCRF that captures global assessment of the spine (“Is the MRI consistent with axSpA: yes/no”) (yes=MRIglobal spine+) and detailed anatomical-based scoring of each discovertebral unit plus lateral and posterior structures. Independently, readers globally assessed SIJ scans for active and/or structural lesions typical of axSpA. We compared the frequency of MRIglobal spine+ and frequencies of different types of spinal lesions according to the presence/absence of axSpA on global evaluation of SIJ scans by ≥5 of 9 readers (MRIglobal SIJ+) and mNY+ sacroiliitis using Fisher’s exact test. Analysis was also stratified by rheumatologist diagnosis.

Results

Among 51 cases with SIJ as well as spine MRI scans and radiographs of the SIJ,19 (37.3%) had MRIglobal SIJ+, and 12 (23.5%) and 7 (13.7%) had MRIglobal spine+ by ≥2 and ≥5 reader agreement, respectively. MRIglobal spine+ occurred significantly more frequently in the presence of mNY+ sacroiliitis and MRIglobal SIJ+ but was also recorded in 4 of 32(12.5%) (≥2 readers) and 1 of 32(3.4%) (≥5 readers) cases that were MRIglobal SIJ- and x-ray negative, all 4 cases being diagnosed with axSpA. Moreover, vertebral corner BME lesions, but not spinal structural lesions, were significantly more frequent in MRIglobal SIJ- cases that had been clinically diagnosed as axSpA versus non-axSpA (Table 1).

Table 1.

Frequency of Spinal MRI lesions According to SIJ Imaging Positive for AxSpA

MRI Spinal Lesions, N (%)MRIglobalSIJ+ (n=19)MRIglobalSIJ- (n=32)P valueMRIglobal SIJ+ and/or mNY+ (n=22)MRIglobal SIJ- and mNY- (n=29)P valueMRIglobal SIJ- and SpA Diagnosis+(n=17)MRIglobal SIJ- and SpA Diagnosis- (n=15)P valueMRIglobal consistent with axSpA (≥2/9 readers agree)8 (42.1%)4 (12.5%)0.048(36.4%)4(13.8%)0.104 (23.5%)0 (0%)0.10MRIglobal consistent with axSpA (≥5/9 readers agree)6 (31.6%)1 (3.1%)0.016 (27.3%)1 (3.4%)0.031 (5.9%)0 (0%)1.0VC BME ≥19 (47.4%)15 (46.9%)46.9% RT 62.5% CT 29.4% GT1.010(45.5%)14(48.3%)1.011 (64.7%)4 (26.7%)0.04VC BME ≥26 (31.6%)10 (31.3%)31.2% RT 55.6% CT 19.6% GT1.06(27.3%)10(34.5%)0.769 (52.9%)1 (6.7%)0.007VC BME ≥36 (31.6%)7 (21.9%)21.9% RT 53.8% CT 13.7% GT0.526(27.3%)7(24.1%)1.07 (41.2%)0 (0%)0.008VC BME ≥45 (26.3%)5 (15.6%)0.475(22.7%)5(17.2%)0.735 (29.4%)0 (0%)0.046Vertebral Endplate BME ≥12 (10.5%)3 (9.4%)1.02(9.1%)3(10.3%)1.02 (11.8%)1 (6.7%)1.0Lateral vertebral BME3 (15.8%)3 (9.4%)0.663(13.6%)3(10.3%)1.03 (17.6%)0 (0%)0.23Facet BME ≥14 (21.1%)1 (3.1%)3.1% RT 20.0% CT 2.0% GT0.064(18.2%)1(3.4%)0.151 (5.9%)0 (0%)1.0Posterior BME ≥15 (26.3%)2 (6.3%)0.095(22.7%)2(6.9%)0.221 (5.9%)1 (6.7%)1.0VC Fat ≥18 (42.1%)42.1% RT 44.4% CT 15.7% GT10 (31.3%)31.2% RT 55.6% CT 19.6% GT0.558(36.4%)10(34.5%)1.05 (29.4%)5 (33.3%)1.0VC Fat ≥27 (36.8%)5 (15.6%)0.107(31.8%)5(17.2%)0.323 (17.6%)2 (13.3%)1.0VC Fat ≥36 (31.6%)31.6% RT 66.7% CT 11.8% GT3 (9.4%)0.066(27.3%)3(10.3%)0.151 (5.9%)2 (13.3%)0.59VC Fat ≥46 (31.6%)1 (3.1%)0.016(27.3%)1(3.4%)0.030 (0%)1 (6.7%)0.47Lateral Fat ≥16 (31.6%)2 (6.3%)0.046(27.3%)2(6.9%)0.060 (0%)2 (13.3%)0.21Erosion ≥13 (15.8%)2 (6.3%)0.353(13.6%)2(6.9%)0.641 (5.9%)1 (6.7%)1.0Bone Spur ≥14 (21.1%)5 (15.6%)0.714(18.2%)5(17.2%)1.04 (23.5%)1 (6.7%)0.34Ankylosis ≥12 (10.5%)0 (0%)0.132(9.1%)0(0%)0.180 (0%)0 (0%)-

Conclusion

Spinal lesions on MRI indicative of axSpA per majority read occurred in about 3% of patients without positive imaging in the SIJ. Frequency of spinal BME lesions was higher in cases with negative SIJ imaging but clinically diagnosed with axSpA.

Disclosure of Interests

None declared

POS1091 LESS RADIOGRAPHIC SPINAL DAMAGE IN PSORIATIC ARTHRITIS PATIENTS COMPARED TO SpA PATIENTS

Background

Psoriatic arthritis (PsA) is an inflammatory joint disease that is traditionally included in the Spondyloarthritis (SpA) spectrum. Prevalence and impact of axial involvement in PsA remain understudied but increasingly affect treatment decisions.

Objectives

A step towards fathoming this issue is to report on baseline radiographic spinal damage in PsA and SpA patients (pts) from 2 prospective multicentre cohort studies in private and academic rheumatology practices.

Methods

Data on PsA pts were from the Belgian Epidemiological Psoriatic Arthritis Study (BEPAS); prospective multicentre cohort in 17 Belgian rheumatology practices. Recruitment was Dec2012-Jul2014. Pts were included when fulfilling the Classification criteria for Psoriatic Arthritis (CASPAR). SpA pts were from a Belgian observational cohort (Be-Giant) of SpA pts fulfilling the ASAS SpA classification criteria. Radiographs of the spine were obtained at baseline and after 2 years. Two calibrated readers evaluated radiographic damage by assessing modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Readers were blinded for time sequence, clinical data and information from other obtained images (radiographs of hands, feet, sacroiliac joints). Consensus scores are described.

Results

In total 461 pts were included in BEPAS. Mean age was 52.79±12.29 years and 43.0% (n=198) were female; average disease duration was 8.5 ± 9.3 years and approximately 34% of the pts reported inflammatory axial pain. From 312 pts spinal radiographs were obtained. At baseline, the vast majority of PsA pts had an mSASSS of 0 (n=273, 87.5%), according to both readers. In 33 PsA pts (10.6%) mSASSS was 2 or more. For the SpA pts percentages were lower but the trend was similar (see Figure 1). Though lesser pts showed abnormalities, the SpA pts with spinal damage show a higher mSASSS, therefore indicating more spinal damage then the PsA pts (p<0.05). Both patient groups show some outliers with high mSASSS, increasing the average mSASSS especially in the SpA cohort (mean mSASSS = 9.1±14.11) compared to the median of 3 (IQR 2-6) in both cohorts

Syndesmophytes are seen in 10.6% and 6.2% of the PsA and SpA pts, respectively. Similar to the mSASSS, SpA pts had more syndesmophytes (mean: 4.4±5.50) compared to PsA pts (mean 2.0±1.45); p<0.05. PsA pts had more often syndesmophytes located in the cervical spine (24/35, 68.6%) compared to the SpA patient group (9/21, 42.9%); p<0.05.

Erosions and especially sclerosis and squaring are uncommon in both patient groups.

Conclusion

Spinal damage is seen in approximately 10% or less of both PsA and SpA pts in these cohorts. SpA pts show higher mSASSS values and more syndesmophytes as compared to the PsA pts. Syndesmophytes in PsA pts are more often located in the cervical spine while the location is more equally distributed in SpA pts.

Table 1.

Spinal damage at baseline of patients from the BEPAS (PsA patients) and Be-Giant (SpA patients) cohorts

PsA patients (n=312)SpA patients (n=260)PsA patients (n=312)SpA patients (n=260)mSASSS ≥2, no of patients33 (10.6%)19 (7.3%)Syndesmophytes (total spine)33 (10.6%)16 (6.2%)mSASSS ≥1, no of patients39 (12.5%)22 (8.5%)mean, (SD)2.0 (1.45)4.4 (5.50)mean, (SD)4.5 (4.24)9.1 (14.11)min, 0.25, median, 0.75, max1.0 1.0 2.0 2.0 8.01.0 1.0 2.5 5.0 22.0min, 0.25, median, 0.75, max1.0 2.0 3.0 6.0 21.01.0 2.0 3.0 10.0 64.0Syndesmophytes (cervical spine)24 (7.7%)9 (3.5%)Erosions ≥1, no of patients13 (4.2%)5 (1.9%)mean, (SD)1.8 (1.32)2.9 (2.89)mean, (SD)1.5 (1.39)1 (0.0)min, 0.25, median, 0.75, max1.0 1.0 1.0 2.0 7.01.0 1.0 2. 0 3.0 10.0min, 0.25, median, 0.75, max1.0 1.0 1.0 1.0 6.01.0 1.0 1.0 1.0 1.0Syndesmophytes (lumbar spine)11 (3.5%)12 (4.6%)Squaring ≥1, no of patientsNo obs.4 (1.5%)mean, (SD)1.9 (0.70)3.7 (4.21)mean, (SD)No obs1.8 (0.96)min, 0.25, median, 0.75, max1.0 1.0 2.0 2.0 3.01.0 1.0 1.0 5.0 12.0min, 0.25, median, 0.75, maxNo obs1.0 1.0 1.5 2.5 3.0Sclerosis ≥1, no of patients2 (0.6%)6 (2.3%)mean, (SD)1.5 (0.71)1.8 (1.33)min, 0.25, median, 0.75, max1.0 1.0 1.5 2.0 2.01.0 1.0 1.0 3.0 4.0

Acknowledgements

The BEPAS study has been supported by MSD Belgium, with noteworthy mentioning of Hermine Leroi.

Disclosure of Interests

None declared

POS0995 VALIDATION OF THE SPARCC MRI-RETIC E-TOOL FOR INCREASING SCORING PROFICIENCY OF MRI LESIONS IN AXIAL SPONDYLOARTHRITIS

Background

The web-based Spondyloarthritis Research Consortium of Canada (SPARCC) real-time iterative calibration (RETIC) modules for scoring MRI lesions in axial spondyloarthritis (axSpA) have been created by SPARCC developers to enable remote training of readers to appropriately use the SPARCC MRI inflammation and structural damage instruments and to attain adequate scoring proficiency.

Objectives

We aimed to test the performance of these modules in enhancing scoring proficiency in comparison to SPARCC developers.

Methods

The SPARCCRETIC SIJ inflammation and structural damage modules are each comprised of 50 DICOM axSpA cases with baseline and follow up scans and an online scoring interface based on SIJ quadrants. Continuous visual real-time feedback regarding concordance/discordance of scoring per SIJ quadrant with expert readers is provided by a color-coding scheme. Reliability is assessed in real-time by intra-class correlation coefficient (ICC), ICC data being provided every 10 cases, which are scored until proficiency targets for ICC are attained. In the present exercise, participants (n=15) from the EuroSpA Imaging project were randomized, stratified by reader expertise in scoring with SPARCC, to one of two reader training strategies (groups A and B) that each comprised 3 stages (25 patients per stage, 2 timepoints, blinded to chronology; independent assessment of Inflammatory and structural lesions): Group A. 1. Review of original SPARCC manuscript describing scoring method. 2. Review of PowerPoint summary of SPARCC method plus completion of SPARCCRETIC module. 3. Re-review of PowerPoint summary. Group B. Same 3-step strategy as A except SPARCCRETIC module completed at stage 3. The reliability of scoring was compared to an expert radiologist (SPARCC developer).

Results

Very good scoring proficiency for status and change scores was evident for SPARCC BME even by non-experienced readers with similar levels of reliability irrespective of prior expertise. The beneficial impact of the SPARCCRETIC module on scoring proficiency was most consistently evident for the scoring of structural lesions and for Strategy B, where the impact was evident for all structural lesions, level of reader expertise, and status as well as change scores (Table 1). Scoring proficiency improved the most for the least experienced readers (Figure 1).

Table 1.

Inter-rater reliability (Status/Change ICC) compared to radiologist SPARCC developer

MRI LesionReader expertiseStrategy AStrategy BStage 1 cases (n=25)Stage 2 cases (n=25)Stage 3 cases (n=25)Stage 1 cases (n=25)Stage 2 cases (n=25)Stage 3 cases (n=25)BMENone (n=4)0.91 / 0.940.83/0.820.77/0.780.82/0.880.65/0.820.88/0.90Intermediate (n=6)0.88/0.880.90/0.900.85/0.900.93/0.940.78/0.800.83/0.80Experienced (n=5)0.92/0.940.90/0.880.92/0.930.83/0.880.84/0.900.89/0.89ANKYLOSISNone (n=4)0.86/0.660.83/0.280.86/0.780.66/0.410.69/0.340.88/0.80Intermediate (n=6)0.89/0.570.83/0.370.92/0.810.82/0.680.74/0.470.93/0.84Experienced (n=5)0.96/0.760.93/0.640.94/0.860.97/0.240.83/0.410.91/0.79BACKFILLNone (n=4)-0.08/-0.050.38/0.220.59/0.380.64/0.130.05/-0.090.47/0.27Intermediate (n=6)0.41/0.130.44/0.420.69/0.390.50/0.220.30/0.300.70/0.42Experienced (n=5)0.82/0.380.55/0.400.91/0.640.65/0.240.21/0.260.71/0.30EROSIONNone (n=4)0.13/-0.080.67/0.420.51/0.330.34/0.330.23/0.080.38/0.37Intermediate (n=6)0.42/0.180.56/0.120.51/0.440.33/0.270.45/0.180.53/0.39Experienced (n=5)0.61/0.330.64/0.340.64/0.420.51/0.270.58/0.110.62/0.31FAT METAPLASIANone (n=4)0.62/0.540.30/0.170.57/0.290.43/0.530.38/0.070.83/0.63Intermediate (n=6)0.49/0.380.59/0.300.79/0.510.57/0.780.50/0.420.81/0.47Experienced (n=5)0.75/0.620.81/0.340.91/0.700.84/0.900.56/0.130.78/0.37

Conclusion

Attaining scoring proficiency for MRI structural lesions in axSpA is difficult but can be consistently improved by using the SPARCCRETIC module, even for experienced readers.

Figure 1.

Disclosure of Interests

Walter P Maksymowych Speakers bureau: Abbvie, Janssen, Novartis, Pfizer, UCB, Consultant of: Abbvie, Boehringer Ingelheim, Celgene, Eli-Lilly, Galapagos, Novartis, Pfizer, UCB, Grant/research support from: Abbvie, Novartis, Pfizer, UCB, Anna Enevold Fløistrup Hadsbjerg Grant/research support from: Novartis, Mikkel Østergaard Consultant of: AbbVie, BMS, Boehringer-Ingelheim, Celgene, Eli Lilly and Company, Galapagos, Gilead, Hospira, Janssen, Merck, Novartis, Novo, Orion, Pfizer, Regeneron, Roche, Sandoz, Sanofi, UCB, Grant/research support from: AbbVie, BMS, Merck, Celgene, Novartis, Raphael Micheroli: None declared, Susanne Juhl Pedersen Grant/research support from: Novartis, Adrian Ciurea: None declared, Nora Vladimirova Grant/research support from: Novartis, Michael J Nissen Speakers bureau: Eli-Lilly, Janssen, Novartis, Consultant of: Abbvie, Celgene, Eli-Lilly, Janssen, Novartis, Pfizer, Kristyna Bubova: None declared, Stephanie Wichuk: None declared, Manouk de Hooge: None declared, Ashish Jacob Mathew Grant/research support from: Novartis, Karlo Pintaric: None declared, Monika Gregová: None declared, Ziga Snoj: None declared, Marie Wetterslev: None declared, Karel Gorican: None declared, Joel Paschke: None declared, Iris Eshed: None declared, Robert G Lambert Paid instructor for: Novartis

OP0150 ASAS RECOMMENDATIONS FOR REQUESTING AND REPORTING IMAGING EXAMINATIONS IN PATIENTS WITH SUSPECTED AXIAL SPONDYLOARTHRITIS

Background

Clinicians face uncertainties in their daily practice when requesting imaging examinations for patients with suspected axial spondyloarthritis (axSpA) or when producing an imaging report because the requirements and desired information of radiologists and rheumatologists / orthopedics alike are sometimes not completely known or understood.

Objectives

This project aimed to develop practical consensus recommendations for the standardized communication around imaging of sacroiliac joints and spine for diagnostic purposes in patients with suspected axSpA or their management in clinical practice.

Methods

An international task force was established combining radiologists (n=7) and rheumatologists (n=13) from the Assessment of SpondyloArthritis international Society (ASAS), two members of Young ASAS and a patient representative. The task force defined the project’s aims and developed a project statement. Then, considering published literature and the work of other groups, two survey rounds were designed, and all ASAS members invited to respond: first, to identify items for further consideration, second, to consider the detail of information to be communicated. Finally, ASAS members discussed the recommendations proposed by the task force during the ASAS annual workshop in January 2022 and voted regarding endorsement of the recommendations.

Results

The final set of recommendations is presented in Figure 1. Six recommendations deal with imaging requests in patients with axSpA. The first three recommendations entail clinical features, patients’ symptoms and risk factors. Recommendation 4 concerns previous imaging and reports and recommendation 5 refers to contraindications to imaging or contrast media. Recommendation 6 is about the suspected diagnosis and possible clinical differential diagnoses and the reason for the examination. Eleven additional recommendations refer to the radiology report. The first point addresses clinical information included in the report. Recommendations 2 to 4 advise on information about the technical conduct of the exam, the use of contrast media and image quality. Imaging findings that should be mentioned in the report if present are listed in recommendations 5 to 7. Finally, recommendations 8 to 11 combine advice for the conclusion, and for suggesting additional imaging or referral to a rheumatology expert if a different physician requested the imaging. The recommendations were endorsed by ASAS with approval from 73% of voting members (43 agreed, 10 rejected, 6 abstained).

Figure 1.

ASAS recommendations for requesting and reporting imaging in patients with suspected axial Spondyloarthritis.

Conclusion

These ASAS recommendations provide guidance for requesting and reporting imaging examinations in the context of axSpA and for standardizing and enhancing communication between rheumatologists and radiologists to improve diagnosis and patient care.

Disclosure of Interests

Torsten Diekhoff Paid instructor for: Novarits, Eli Lilly, MSD, Canon MS, Consultant of: Eli Lilly, Iris Eshed: None declared, Chiara Giraudo: None declared, Kay-Geert Hermann: None declared, Manouk de Hooge: None declared, Lennart Jans: None declared, Anne Grethe Jurik: None declared, Robert G Lambert: None declared, Pedro M Machado: None declared, Walter P Maksymowych: None declared, Michael Mallinson: None declared, Helena Marzo-Ortega: None declared, Victoria Navarro-Compán: None declared, Susanne Juhl Pedersen: None declared, Mikkel Østergaard: None declared, Monique Reijnierse: None declared, Martin Rudwaleit: None declared, Fernando Sommerfleck: None declared, Ulrich Weber: None declared, Xenofon Baraliakos: None declared, Denis Poddubnyy: None declared

OP0251 DATA-DRIVEN DEFINITIONS BASED ON INFLAMMATORY LESIONS FOR A POSITIVE MRI OF THE SPINE CONSISTENT WITH AXIAL SPONDYLOARTHRITIS

Background:

The ASAS definition of a positive MRI for inflammation in the spine (ASAS-MRIspine+) is intended for classification of patients as having axSpA but is often misused for diagnostic purposes. This is problematic because bone marrow edema (BME) in the spine may occur in 20-40% of those with mechanical back disorders. The ASAS MRI group has generated updated consensus lesion definitions which have been validated on MRI spine images from the ASAS Classification Cohort.

Objectives:

We aimed to identify quantitative cut-offs based on numbers of vertebral corners that define ASAS-MRIspine+, there being two gold standards: A. majority central reader decision as to the presence of spine MRI findings consistent with axSpA B. rheumatologist expert opinion diagnosis of axSpA.

Methods:

Eight ASAS-MRI readers recorded MRI lesions in the spine according to recently updated ASAS definitions from 62 cases in an eCRF that comprises global assessment (MRI consistent with axSpA? (yes/no)), and detailed scoring of lesions for all sites in the spine. We calculated sensitivity and specificity for numbers of vertebral corners with BME where a majority of readers (≥5/8) agreed as to the presence of MRI findings consistent with axSpA. We selected cut-offs with ≥95% specificity. These cut-offs were analyzed for their predictive utility for rheumatologist diagnosis of axSpA by calculating positive and negative predictive values (PPV, NPV) and selecting cut-offs with PPV ≥95%. Both criteria were considered requirements for designation of MRI cut-offs defining ASAS-MRIspine+.

Results:

MRI findings consistent with axSpA were observed by majority read in 8 (20%) of 40 cases diagnosed with axSpA, and 0 (0%) of 19 cases without axSpA. Cut-offs achieving specificity of ≥95% for MRI findings consistent with axSpA were 4 vertebral corners (sensitivity 75%) for all cases, 3 vertebral corners (sensitivity 37.5%) for cases with ≥1 additional location with inflammation, 1 vertebral corner (sensitivity 62.5%) in cases with ≥2 vertebral corner fat lesions (Table 1). All of the above cut-offs also had very high PPV (≥95%) for diagnosis of axSpA in cases diagnosed by the rheumatologist (Table 2).

Table 1.

Majority readers agree MRI findings consistent with axSpA are present is the gold-standard external reference

MRI cut-offsSensitivity (95%CI)Specificity (95%CI)BME in ≥2 vertebral corners87.5 (47.3 - 99.7)87.0 (75.1 - 94.6)BME in ≥ 3 vertebral corners87.5 (47.3 - 99.7)94.4 (84.6 - 98.8)BME in ≥4 vertebral corners75.0 (34.9 - 96.8)98.2 (90.1 - 100.0)Cases with ≥1 additional non-corner site inflammatory lesionBME in ≥2 vertebral corners37.5 (8.5 - 75.5)94.4 (84.6 - 98.8)BME in ≥3 vertebral corners37.5 (8.5 - 75.5)98.2 (90.1-100.0)Cases with ≥2 vertebral corner fat lesionsBME in ≥1 vertebral corner62.5 (24.5 - 91.5)100.0 (93.4-100.0)BME in ≥2 vertebral corners62.5 (24.5 - 91.5)100.0 (93.4-100.0)Table 2.

Predictive values of cut-offs for number of vertebral corners with BME according to the diagnostic ascertainment of the rheumatologist

MRI cut-offsSensitivity (95%CI)Specificity (95%CI)PPVNPVMRI findings consistent with axSpA ≥any 2 readers52.5 (36.1 - 68.5)94.7 (74.0 - 99.9)95.5 (75.3 - 99.3)48.6 (40.2 - 57.2)MRI findings consistent with axSpA ≥majority read20.0 (9.1 - 35.6)100.0 (82.4 - 100.0)100.037.3 (33.7 - 40.9)BME in ≥ 4 vertebral corners17.5 (7.3 - 32.8100.0 (82.4 - 100.0)100.036.5 (33.3 - 39.9)Cases with ≥1 additional inflammatory lesionBME in ≥ 3 vertebral corners10.00 (2.8 - 23.7)100.00 (82.4 - 100.0)100.034.5 (32.2 - 36.9)Cases with ≥2 vertebral corner fat lesionsBME in ≥1 vertebral corner12.50 (4.2 - 26.8)100.00 (82.4 - 100.0)100.035.2 (32.6 - 37.9)

Conclusion:

A cut-off of BME in ≥4 vertebral corners, or ≥3 corners in the setting of additional inflammatory lesions at other locations or corner fat, are primary candidates for defining ASAS-MRIspine+. These cut-offs apply to typical patients referred to a rheumatologist with a high index of suspicion of axSpA and may not be appropriate in other populations.

Disclosure of Interests:

None declared

OP0075 SPINAL RADIOGRAPHIC PROGRESSION IN AXIAL SPONDYLOARTHRITIS AND THE IMPACT OF CLASSIFICATION AS NONRADIOGRAPHIC VERSUS RADIOGRAPHIC DISEASE

Background:

Data on spinal radiographic progression is more limited in nonradiographic axial spondyloarthritis (nr-axSpA) than in the radiographic disease state (r-axSpA). It remains unclear, whether radiographic sacroiliitis is by itself associated with progression of spinal structural damage.

Objectives:

To investigate whether spinal radiographic progression relates to structural damage at the sacroiliac level in axSpA by means of statistical mediation analyses in a large prospective real-life cohort of patients with axSpA.

Methods:

Patients from the Swiss Clinical Quality Management cohort were included if they fulfilled the ASAS classification criteria and could be classified as nr-axSpA or r-axSpA after central scoring of pelvis radiographs. Spinal radiographs performed every 2 years were scored according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). The relationship between classification status and spinal progression over 2 years was investigated using binomial generalized estimating equations models with adjustment for sex, ankylosing spondylitis disease activity score (ASDAS) and tumor necrosis factor inhibitor treatment. Baseline spinal damage was considered an intermediate variable and included in sensitivity analyses, as were additional variables potentially influencing radiographic progression.

Results:

In total, 88 nr-axSpA and 418 r-axSpA patients contributed to data for 725 radiographic intervals (Table 1). Mean (SD) mSASSS change over 2 years was 0.16 (0.62) units in nr-axSpA and 0.92 (2.78) units in r-axSpA, p=0.01. Nr-axSpA was associated with a significantly lower progression over 2 years (defined as an increase in ≥2 mSASSS units) in adjusted analyses (OR 0.33, 95%CI 0.13; 0.83), confirmed with progression defined as the formation of ≥1 syndesmophyte. Mediation analyses revealed that sacroiliitis exerted its effect on spinal progression indirectly by being associated with the appearance of a first syndesmophyte (OR 0.09, 95%CI 0.02; 0.36 for nr-axSpA vs r-axSpA) (Fig. 1 and 2). Baseline syndesmophytes were predictors of further progression.

Table 1.

Baseline characteristics at first radiograph.

ParameterN506nr-axSpAN = 88r-axSpAN = 418PFemale sex, %50654.533.7<0.001Age, y50639.5±11.140.4±11.00.52Symptom duration, y49810.0±9.914.0±9.8<0.001HLA-B27 positive, %45271.680.70.09BASDAI4274.6±2.04.2±2.30.26ASDAS4082.8±0.92.8±1.10.74Elevated CRP, %42230.640.60.14BASFI4332.8±2.23.1±2.50.71BASMI4351.1±1.42.2±2.0<0.001mSASSS5060.9±1.56.8±12.7<0.001Syndesmophytes, %5069.135.2<0.001On TNFi, %50619.336.40.002Fig. 1.

Modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) for individual patients plotted as a function of duration since symptom onset.

Fig. 2.

Two-year mSASSS progression depicted in a cumulative probability plot. Progression was defined as an increase in mSASSS of at least 2 units (dotted line) in 2 years.

Conclusion:

Spinal structural damage is mainly restricted to patients with r-axSpA, leading to relevant prognostic and therapeutic implications.

Disclosure of Interests:

Monika Hebeisen: None declared, Raphael Micheroli: None declared, Almut Scherer: None declared, Xenofon Baraliakos Grant/research support from: Grant/research support from: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen, Consultant of: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen, Speakers bureau: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen, Manouk de Hooge: None declared, Désirée van der Heijde Consultant of: AbbVie, Amgen, Astellas, AstraZeneca, BMS, Boehringer Ingelheim, Celgene, Cyxone, Daiichi, Eisai, Eli-Lilly, Galapagos, Gilead Sciences, Inc., Glaxo-Smith-Kline, Janssen, Merck, Novartis, Pfizer, Regeneron, Roche, Sanofi, Takeda, UCB Pharma; Director of Imaging Rheumatology BV, Robert B.M. Landewé Consultant of: AbbVie; AstraZeneca; Bristol-Myers Squibb; Eli Lilly & Co.; Galapagos NV; Novartis; Pfizer; UCB Pharma, Kristina Buerki: None declared, Michael Nissen Grant/research support from: Abbvie, Consultant of: Novartis, Lilly, Abbvie, Celgene and Pfizer, Speakers bureau: Novartis, Lilly, Abbvie, Celgene and Pfizer, Burkhard Moeller: None declared, Pascal Zufferey: None declared, Pascale Exer: None declared, Adrian Ciurea Consultant of: Consulting and/or speaking fees from AbbVie, Bristol-Myers Squibb, Celgene, Eli Lilly, Merck Sharp & Dohme, Novartis and Pfizer.

OP0055 MINIMAL RADIOGRAPHIC DAMAGE OF SACROILIAC JOINTS DETECTED IN PSORIATIC ARTHRITIS PATIENTS

Background:

Psoriatic arthritis (PsA) is an inflammatory joint disease that is traditionally included in the Spondyloarthritis (SpA) spectrum. Prevalence and impact of axial involvement in PsA remains understudied but increasingly affects treatment decisions.

Objectives:

The first step, in this multi-purpose radiographic study, is to report on baseline radiographic damage of the sacroiliac joints (SIJ) in PsA patients from a prospective multicentre cohort study in private and academic rheumatology practices.

Methods:

Data from the Belgian Epidemiological Psoriatic Arthritis Study (BEPAS), a prospective multicentre cohort involving 17 Belgian rheumatology practices. Recruitment was from December 2012 until July 2014. Patients were included in the study when the local rheumatologist could diagnose an existing or new PsA and when patients fulfilled the Classification criteria for Psoriatic Arthritis (CASPAR). Radiographs of the SIJ were obtained at baseline and after 2 years. Two calibrated readers assessed radiographic damage by grading the SIJ according to the modified New York (mNY) criteria. When assessing the images, readers were blinded for clinical data and information from other obtained images (radiographs of the hands, feet and spine). Individual scores as well as consensus scores are described.

Results:

In total 461 patients where included in BEPAS. Mean age was 52.79±12.29 years and 43.0% (n=198) were female; average disease duration was 8.5 ± 9.3 yrs and approximately 34% of the patients report inflammatory axial pain. From 338 patients SIJ radiographs were obtained. At baseline, the vast majority of patients did not fulfil the mNY criteria (n=325, 96.2%), according to both readers. In 8 cases (2.4%) there was concordance on fulfilment of the mNY criteria. Discordant cases (n=5, 1.4%) were equally distributed. Agreement between the 2 readers was good with 98.5% overall agreement and kappa=0.75. Therefore, with a more sensitive approach (any of the 2 readers scores mNY positive) we see slight differences; 13 patients (3.8%) fulfil the mNY criteria. Table 1 shows radiographic damage by individual readers

Table.

Baseline data on radiographic damage of the sacroiliac joints in Belgian patients with newly diagnosed or existing PsA included in the BEPAS.

N=338Right sacroiliac jointLeft sacroiliac jointGradesType of lesionReader 1Reader 2Reader 1Reader 20No abnormalities298 (88.2%)301 (89.1%)298 (88.2%)296 (87.6%)1Indefinite abnormalities32 (9.5%)23 (6.8%)27 (8.0%)23 (6.8%)2-3Abnormalities5 (1.5%)12 (3.6%)9 (2.7%)19 (5.6%)Erosion3 (0.9%)11 (3.3%)4 (1.2%)18 (5.3%)Sclerosis4 (1.2%)12 (3.6%)5 (1.5%)13 (3.9%)Joint space alteration (narrowing or widening)1 (0.3%)1 (0.3%)4 (1.2%)2 (0.6%)Partial ankylosis2 (0.6%)3 (0.9%)5 (1.5%)8 (2.4%)4Total ankylosis3 (0.9%)2 (0.6%)4 (1.2%)-

In 128 patients (37.9%) a follow-up x-ray after 2 years was available. In 124 patients (96.9%) there was reader agreement on mNY negative status. There was disagreement between readers on a positive mNY in 2 patients (equally distributed) and agreement on 2 patients (1.6%). There were no patients with consensus between readers on the change in mNY over 2 years, but 1 reader reported 1 patient becoming mNY positive after 2 years.

Conclusion:

Despite the patient self-identified presence of axial disease in up to 34% in this cohort of PsA patients, there was minimal radiographic damage on SIJ, suggesting that SIJ disease is not a major manifestation of PsA.

Disclosure of Interests:

Manouk de Hooge: None declared, Alla Ishchenko: None declared, Serge Steinfeld: None declared, Adrien Nzeusseu Toukap Grant/research support from: AbbVie, Celgene Corporation, Janssen, Pfizer, UCB – grant/research support, Consultant of: AbbVie, Eli Lilly, Janssen, Novartis, UCB – consultant, Speakers bureau: AbbVie, Eli Lilly, Janssen, Novartis, UCB – advisory board member, Dirk Elewaut: None declared, Hermine Leroi Employee of: MSD Belgium, Rik Lories Grant/research support from: AbbVie, Boehringer Ingelheim, Celgene Corporation, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Pfizer, Samumed and UCB – grant/research support (on behalf of Leuven Research and Development), Consultant of: AbbVie, Boehringer Ingelheim, Celgene Corporation, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Pfizer, Samumed and UCB – consultant (on behalf of Leuven Research and Development), Speakers bureau: AbbVie, Boehringer Ingelheim, Celgene Corporation, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Pfizer, Samumed and UCB – speaker (on behalf of Leuven Research and Development), Kurt de Vlam Grant/research support from: Celgene, Eli Lilly, Pfizer Inc, Consultant of: AbbVie, Eli Lilly, Galapagos, Johnson & Johnson, Novartis, Pfizer Inc, UCB, Filip van den Bosch Consultant of: AbbVie, Celgene Corporation, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, and UCB, Speakers bureau: AbbVie, Celgene Corporation, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, and UCB

FRI0317 CONSENSUS DEFINITIONS FOR MRI LESIONS IN THE SPINE OF PATIENTS WITH AXIAL SPONDYLOARTHRITIS: FIRST ANALYSIS FROM THE ASSESSMENTS IN SPONDYLOARTHRITIS INTERNATIONAL SOCIETY CLASSIFICATION COHORT

Background:

A recent consensus from the ASAS MRI group has culminated in updated spine lesion definitions for axial spondyloarthritis (ASAS_MRI_defn)1. There has been no central reader evaluation of MRI scans from the ASAS Classification Cohort (ASAS-CC)2to determine the spectrum of MRI lesions in the spine in this cohort.

Objectives:

To determine the spectrum of active and structural lesions on MRI images of the spine from the ASAS-CC according to the consensus ASAS_MRI_defnupdate.

Methods:

ASAS_MRI_defnwere recorded by 9 central readers in an eCRF for global assessment and detailed scoring of each discovertebral unit and postero-lateral structures. Vertebral corner bone marrow edema (VCBME) and corner fat (VCFAT) lesions were recorded if present on 2 slices; facet joint, lateral, and posterior inflammatory lesions were recorded if present on a single slice. Vertebral corner erosion, bone spurs, and ankylosis were each scored on a single slice. Comparison of active and structural lesion frequencies by local rheumatologist diagnosis of axSpA was assessed descriptively according to ≥2 and majority reader (≥5/9) concordant data.

Results:

MRI scans of the spine were available from 69 cases with axSpA diagnosed in 44/64 (68.8%). VCBME was most frequent with ≥1 lesion in 32(46.4%) and 19 (27.5%) by ≥2 and ≥5/9 readers, respectively. VCFAT was the most frequent structural lesion with ≥1 lesion in 24 (34.8%) and 14 (20.3%) by ≥2 and ≥5/9 readers, respectively. There were significantly more VCBME lesions in axSpA patients than non-axSpA (mean(SD):1.8(2.7) vs 0.3 (0.5)) (p<0.001) while differences in VCFAT were not significant (Table). The presence of ≥2 VCBME had 90-95% specificity for axSpA. Significantly more VCBME and VCFAT were observed in the setting of radiographic sacroiliitis (modified New York criteria (mNY)).

Conclusion:

Spine lesions on MRI are relatively frequent in patients with undiagnosed back pain presenting to the rheumatologist. The presence of ≥2 VCBME, but not VCFAT, may have some diagnostic utility.

References:

[1]Maksymowych WP, et al. Arthritis Rheumatol 70 (suppl 10): 654, 2018

[2]Rudwaleit et al. Ann Rheum Dis 2009;68: 777-83

Vertebral Corner MRI lesionsmajority of readers (>=5)≥2 readersaxSpA=Yes (n=44)axSpA=No (n=20)p-valueaxSpA=Yes (n=44)axSpA=No (n=20)p-valueCorner Fat ≥112 (27.3%)2 (10%)0.1917 (38.6%)7 (35%)0.78Corner Fat ≥210 (22.7%)2 (10%)0.3113 (29.5%)4 (20%)0.64Corner Fat ≥38 (18.2%)1 (5%)0.2510 (22.7%)3 (15%)0.74Corner Fat ≥47 (15.9%)1 (5%)0.429 (20.5%)2 (10%)0.48Corner BME ≥117 (38.6%)1 (5%)0.00625 (54.5%)6 (30%)0.047Corner BME ≥215 (34.1%)1 (5%)0.01319 (43.2%)2 (10%)0.009Corner BME ≥311 (25%)0 (0%)0.01316 (36.4%)1 (5%)0.008Corner BME ≥48 (18.2%)0 (0%)0.09412 (27.3%)1 (5%)0.048mNY=Yes (n=10)mNY=No (n=49)p-valuemNY=Yes (n=10)mNY=No (n=49)p-valueCorner Fat ≥15 (50%)9 (18.4%)0.0475 (50%)17 (34.7%)0.48Corner Fat ≥25 (50%)7 (14.3%)0.0225 (50%)11 (22.4%)0.12Corner Fat ≥34 (40%)5 (10.2%)0.0364 (40%)9 (18.4%)0.20Corner Fat ≥44 (40%)4 (8.2%)0.0224 (40%)7 (14.3%)0.079Corner BME ≥15 (50%)11 (22.4%)0.1167 (70%)22 (44.9%)0.18Corner BME ≥25 (50%)9 (18.4%)0.0475 (50%)14 (28.6%)0.27Corner BME ≥35 (50%)6 (12.2%)0.0145 (50%)11 (22.4%)0.12Corner BME ≥45 (50%)3 (6.1%)0.0025 (50%)7 (14.3%)0.022

Disclosure of Interests:

Walter P. Maksymowych Grant/research support from: AbbVie, Novartis, Pfizer, and UCB, Consultant of: AbbVie, Boehringer Ingelheim, Celgene, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, and UCB, Employee of: Chief Medical Officer of CARE Arthritis Limited, Speakers bureau: AbbVie, Janssen, Novartis, Pfizer, and UCB, Iris Eshed: None declared, Pedro M Machado Consultant of: PMM: Abbvie, Celgene, Janssen, Lilly, MSD, Novartis, Pfizer, Roche and UCB, Speakers bureau: PMM: Abbvie, BMS, Lilly, MSD, Novartis, Pfizer, Roche and UCB, Susanne Juhl Pedersen Grant/research support from: Novartis, Ulrich Weber: None declared, Manouk de Hooge: None declared, Joachim Sieper Consultant of: AbbVie, Boehringer Ingelheim, Eli Lilly and Company, Janssen, Merck, Novartis, Pfizer, Roche, and UCB Pharma, Speakers bureau: AbbVie, Boehringer Ingelheim, Eli Lilly and Company, Janssen, Merck, Novartis, Pfizer, Roche, and UCB Pharma, Stephanie Wichuk: None declared, Denis Poddubnyy Grant/research support from: AbbVie, MSD, Novartis, and Pfizer, Consultant of: AbbVie, Bristol-Myers Squibb, Eli Lilly, MSD, Novartis, Pfizer, Roche, UCB, Speakers bureau: AbbVie, Bristol-Myers Squibb, Eli Lilly, MSD, Novartis, Pfizer, Roche, UCB, Martin Rudwaleit Consultant of: AbbVie, BMS, Celgene, Janssen, Eli Lilly, MSD, Novartis, Pfizer, Roche, UCB Pharma, Désirée van der Heijde Consultant of: AbbVie, Amgen, Astellas, AstraZeneca, BMS, Boehringer Ingelheim, Celgene, Cyxone, Daiichi, Eisai, Eli-Lilly, Galapagos, Gilead Sciences, Inc., Glaxo-Smith-Kline, Janssen, Merck, Novartis, Pfizer, Regeneron, Roche, Sanofi, Takeda, UCB Pharma; Director of Imaging Rheumatology BV, Robert B.M. Landewé Consultant of: AbbVie; AstraZeneca; Bristol-Myers Squibb; Eli Lilly & Co.; Galapagos NV; Novartis; Pfizer; UCB Pharma, Robert G Lambert: None declared, Mikkel Ǿstergaard Grant/research support from: AbbVie, Bristol-Myers Squibb, Celgene, Merck, and Novartis, Consultant of: AbbVie, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Eli Lilly, Hospira, Janssen, Merck, Novartis, Novo Nordisk, Orion, Pfizer, Regeneron, Roche, Sandoz, Sanofi, and UCB, Speakers bureau: AbbVie, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Eli Lilly, Hospira, Janssen, Merck, Novartis, Novo Nordisk, Orion, Pfizer, Regeneron, Roche, Sandoz, Sanofi, and UCB, Xenofon Baraliakos Grant/research support from: Grant/research support from: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen, Consultant of: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen, Speakers bureau: AbbVie, BMS, Celgene, Chugai, Merck, Novartis, Pfizer, UCB and Werfen

FRI0304 SERUM IGG-UNDERGALACTOSYLATION PROFILES REFLECT CUMULATIVE EXPOSURE TO SYSTEMIC INFLAMMATION IN SPONDYLOARTHRITIS PATIENTS

Background:

Inflammation in spondyloarthritis (SpA) is often not reflected by elevated acute phase reactants such as C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR). It has been shown that IgG glycosylation patterns are subject to specific alterations (i.e. undergalactosylation) in chronic inflammatory diseases. Since these changes only occur in persistent inflammatory processes, lasting at least one to two t1/2of IgG (24 days), it was hypothesized that IgG-glycan profiles could serve as a surrogate marker for chronic inflammation in SpA patients.

Objectives:

To assess the value of serum IgG-undergalactosylation in SpA patients in relation to outcome measures for disease activity, determined by patient reported outcomes, serum inflammatory markers and imaging outcomes.

Methods:

Serum samples were obtained from SpA patients at the baseline visit of Be-Giant: a Belgian observational cohort including SpA patients who fulfill the ASAS classification criteria for axial or peripheral SpA. IgG Fc N-glycans were released directly in whole serum by endo-β-N-acetyl-glucosaminidase fromStreptococcus pyogenes(EndoS), fluorescently labeled with ATPS and analyzed by capillary electrophoresis, rendering glycan profiles with six peaks (Figure 1). Relative peak heights were combined in the undergalactosylation score (UGS), capturing the relative upregulation of non-galactosylated glycans normalized to the total peak height (1). Baseline radiographs (X-SIJ) and magnetic resonance images (MRI) of the sacroiliac joints (SIJ) were assessed by three calibrated readers for sacroiliitis (fulfillment of the modified New York criteria; grading 0 to 4 per SIJ) and for inflammatory lesions according to the Spondyloarthritis Research Consortium of Canada (SPARCC) method (score from 0 – 72) respectively. Grades and inflammatory lesions that were seen by at least 2 readers were used for further analysis.

Figure 1.

Example of a serum IgG-specific glycan profile. Adapted from (1), with permission.

Results:

Glycan profiles were obtained from 376 SpA patients; UGS was scaled (mean = 0, SD = 1) for further analysis. UGS was independently associated with ASDAS-CRP (β1= 0.15, 95% CI 0.04 – 0.26, p = 0.006) and BASFI (β1= 0.44, 95% CI 0.16 – 0.72, p = 0.002) but not with BASDAI (β1= 0.12, 95% CI -0.13 – 0.38, p = 0.34). UGS showed a weak to moderate correlation with CRP (Rs= 0.30, p < 0.001) and ESR (Rs= 0.27, p <0.001). In axial SpA, UGS was significantly higher in patients with ankylosing spondylitis compared to non-radiographic axial SpA (OR = 2.41, 95% CI 1.60 – 3.73, p < 0.001) and showed an independent association with the total grading of the SIJ (β1= 0.44, 95% CI 0.09 – 0.80, p = 0.01, Figure 2) and SPARCC score (β1= 2.64, 95% CI 0.98 – 4.31, p = 0.002). All models were adjusted for age, gender, BMI, CRP, anti-TNF treatment and symptom duration.

Conclusion:

This study shows and independent association of serum IgG undergalactosylation with disease activity and functional impairment in SpA patients. Moreover, UGS was significantly higher in advanced compared to early-stage axial disease and therefore may reflect the cumulative exposure to systemic inflammation.

References:

[1]Vanderschaeghe D, Meuris L, Raes T, et al. Endoglycosidase S Enables a Highly Simplified Clinical Chemistry Procedure for Direct Assessment of Serum IgG Undergalactosylation in Chronic Inflammatory Disease. Mol Cell Proteomics. 2018;17(12):2508-17.

Figure 2.

Correlation between UGS and X-SIJ total grading of sacroiliitis. R = Spearman’s correlation coefficient.

Disclosure of Interests:

Ann-Sophie De Craemer: None declared, Zuzanna Lukasik: None declared, Leander Meuris: None declared, Liselotte Deroo: None declared, Thomas Renson: None declared, Manouk de Hooge: None declared, Philippe Carron: None declared, Annelies Van Hecke: None declared, Nico Callewaert: None declared, Filip van den Bosch Consultant of: AbbVie, Celgene Corporation, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, and UCB, Speakers bureau: AbbVie, Celgene Corporation, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, and UCB, Dirk Elewaut: None declared

Evolution of body-wall musculature in the Platyhelminthes (Acoelomorpha, Catenulida, Rhabditophora)

In an effort to understand the phylogeny of the Platyhelminthes, the patterns of body-wall musculature of flatworms were studied using fluorescence microscopy and Alexa-488-labeled phalloidin. Species of the Catenulida have a simple orthogonal gridwork of longitudinal and circular muscles. Members of the Rhabditophora have the same gridwork of musculature, but also have diagonal muscles over their entire body. Although a few species of Acoelomorpha possessed a simple orthogonal grid of musculature, most species typically have distinctly different patterns of dorsal and ventral body-wall musculature that include sets of longitudinal, circular, U-shaped, and several kinds of diagonal muscles. Several distinct patterns of musculature were identified, including 8 patterns in 11 families of acoels. These patterns have proven to be useful in clarifying the phylogeny of the Acoelomorpha, particularly with regard to the higher acoels. Patterns of musculature as well as other morphological characters are used here for revisions of acoel systematics, including the return of Eumecynostomum sanguineum (Mecynostomidae) to the genus Aphanostoma (Convolutidae), the revision of the family Childiidae, and the formation of a new family, Actinoposthiidae.

Musculature of the facultative parasite Urastoma cyprinae (Platyhelminthes)

In an effort to understand how the feeding motions of Urastoma cyprinae are generated, the arrangement of its musculature was studied using fluorescence microscopy of phalloidin-linked fluorescent stains and conventional light histology and transmission electron microscopy. BODIPY 558/568 phalloidin and Alexa 488 phalloidin resolved a meshwork of ribbon-shaped body-wall muscles as well as inner-body musculature associated with the pharynx and male copulatory organ. The general pattern of body-wall muscles in U. cyprinae is similar to that of other rhabdocoel turbellarians in consisting only of circular, longitudinal, and diagonal fibers; the arrangement of these muscles readily correlates with the bending motions the animal undergoes as it feeds at the surface of gills in bivalves it parasitizes. The orogenital atrium of U. cyprinae lies at the posterior apex of the body, opening at a terminal pore. As evidenced by the arrangement of its epithelium and musculature, it appears to be an invagination of the body wall and comes closest of any such duct studied in turbellarians to satisfying the hypothetical model of a "pseudopharynx," ostensibly adapted as an organ for swallowing and so supplementing the ingestive role of the animal's true pharynx.