Matrix orthogonality in the plane versus scalar orthogonality in a Riemann surface

We consider a non-Hermitian matrix orthogonality on a contour in the complex plane. Given a diagonalizable and rational matrix valued weight, we show that the Christoffel–Darboux (CD) kernel, which is built in terms of matrix orthogonal polynomials, is equivalent to a scalar valued reproducing kernel of meromorphic functions in a Riemann surface. If this Riemann surface has genus $0$, then the matrix valued CD kernel is equivalent to a scalar reproducing kernel of polynomials in the plane. Interestingly, this scalar reproducing kernel is not necessarily a scalar CD kernel. As an application of our result, we show that the correlation kernel of certain doubly periodic lozenge tiling models admits a double contour integral representation involving only a scalar CD kernel. This simplifies a formula of Duits and Kuijlaars.

POS1134 COMPARATIVE ANALYSIS OF THE CLINICAL AND LABORATORY PROPERTIES OF GOUT, OSTEOARTHRITIS, AND CALCIUM PYROPHOSPHATE DEPOSITION DISEASE

Background:The clinical differentiation between gout, osteoarthritis (OA), and calcium pyrophosphate deposition disease (CPPD) still remains a hurdle in daily practice without imaging or arthrocentesis. Although a plethora of clinical data exists, reliable predictor biomarkers for all but gout are still missing.Objectives:To explore an association between common physical examination, ultrasound and laboratory findings and gout, OA, and CPPD, which can in turn provide reliable diagnostic predictions.Methods:277 patients were retrospectively analysed using ANOVA with Scheffe’s post hoc tests and conditional inference trees regarding biomarkers such as age, sex, body mass index, hypertension, renal status, cumulative affected joint size, number of afflicted joints, double contour sign, intracartiliginous double contour sign, degree of vascularization on ultrasound (DoV), uric acid, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), ferritin, and leucocyte count. Simple linear regressions were carried out to explore associations between increased inflammatory parameters and the above-mentioned biomarkers. Statistically significant associations were defined as p values < 0.05.Results:The male sex was associated with gout (p value < 0.05 vs CPPD and < 0.05 vs OA). OA affected younger patients than CPPD (mean 64.5 vs 73.1 years, p < 0.05). Hypertension was correlated with gout (p < 0.05) and CPPD (p < 0.05), impaired renal status with gout when compared to OA (p < 0.05) but not compared to CPPD (p 0.21). A higher number of involved joints was associated with gout (mean 2.2 joints) compared to OA (1.0, p < 0.05) and CPPD (1.6, p 0.01). The double contour sign was not able to differentiate gout and CPPD with a sensitivity/specificity of 71%/55% for gout and 59%/39% for CPPD. The intracartilaginous double contour sign was specific for CPPD (99%) but with a low sensitivity of 26%. DoV was significantly associated with gout (vs OA, p < 0.05) and CPPD (vs OA, p < 0.05). Unsurprisingly, uric acid was associated with gout while ESR and CRP were increased in gout and CPPD, but not in OA. Some associations were statistically significant but arguably clinically unimportant. Conditional inference trees were able to exclude OA (specificity 97.5%) and CPPD (specificity 94.0%) as possible differentials based on just uric acid, CRP, hypertension, and sex, and diagnose gout with a sensitivity of 95.1%, summarized in Figure 1. Linear regressions demonstrated an elevated CRP response in people suffering from type II diabetes, higher cumulative joint points score, number of affected joints, as well as elevated uric acid, ESR, and leucocyte count.Figure 1.Conditional inference tree using unbiased recursive partitioning to reliably differentiate between gout, osteoarthritis, and calcium pyrophosphate deposition disease.Conclusion:Gout can be reliably diagnosed, simultaneously excluding OA and CPPD as differential diagnoses by conditional inference trees using just four biomarkers. A correlation between inflammatory reaction severity based on CRP levels was found in patients suffering from type II diabetes, more or larger joint involvement and elevated uric acid levels. The double contour sign remains a questionable differentiator between gout and CPPD with a sensitivity/specificity of 71%/55% for gout and 59%/39% for CPPD, similar to findings reported by Löffler et al (1) with a sensitivity/specificity of only 64%/52% for gout.References:[1]Löffler C, Sattler H, Peters L, Löffler U, Uppenkamp M, Bergner R. Distinguishing gouty arthritis from calcium pyrophosphate disease and other arthritides. J Rheumatol 2015; 42(3):513–20.Disclosure of Interests:Dmitrij Kravchenko Shareholder of: Pfizer, Raoul Bergner: None declared, Charlotte Behning: None declared, Valentin Schäfer Speakers bureau: AbbVie, Novartis, BMS, Chugai, Celgene, Medac, Sanofi, Lilly, Hexal, Pfizer, Janssen, Roche, Schire, Onkowissen, Royal College London, Consultant of: Novartis, Chugai, AbbVie, Celgene, Sanofi, Lilly, Hexal, Pfizer, Amgen, BMS, Roche, Gilead, Medac, Grant/research support from: Novartis, Hexal, Lilly, Roche, Celgene, Universität Bonn.

OP0204 URATE CRYSTAL DEPOSITIONS ARE ASSOCIATED WITH INFLAMMATORY MARKERS AND CAROTID PLAQUES INDICATING SUBCLINICAL INFLAMMATION IN GOUT; BASELINE RESULTS FROM THE NOR-GOUT STUDY

Background:In gout patients the extent of monosodium urate (MSU) crystal depositions can be quantitated by use of ultrasound. Gout may be associated with atherosclerotic disease which might be related to low-grade inflammation. Calprotectin is a major granulocyte protein reflecting the level of systemic inflammation.Objectives:To explore whether the extent of MSU crystal depositions is associated with low grade systemic inflammation as assessed by calprotectin/C-reactive protein (CRP) and with carotid pathologies in asymptomatic gout patients.Methods:The baseline data from NOR-GOUT, a prospective study of patients with crystal-proven gout with increased serum urate levels (>360 μmol/L), were used. All patients were assessed by ultrasound (GE Logiq E9 machine) to assess MSU depositions (OMERACT definitions; double contour (DC), tophi and aggregates) with bilateral assessment of wrist, MCP2, knee, ankle, MTP1 and insertions of triceps, quadriceps, proximal/distal patellar and Achilles tendons, all scored semi-quantitatively 0-3. Bilateral B-mode ultrasound assessments of the carotid arteries examined carotid intima-media thickness (cIMT; increased thickness >0.9mm). Atherosclerotic plaques were identified as protrusions of ≥1.5 mm or ≥ 2 times the adjacent IMT. Sum scores of each of the ultrasound elementary lesions for MSU depositions were calculated and the associations with calprotectin (plasma assessed by ELISA (Calpro), normal levels <910 µg/L), CRP (routine assessment, normal levels <4mg/L) as well as cIMT and presence of carotid plaque were explored. Correlations were performed by use of Spearman and differences between group was investigated by Mann-Whitney test.Results:A total of 202 gout patients without flare were included (95.5% men, mean (SD) age of 56.5 (13.8) years, 7.9 (7.7) years since first flare). The mean (SD) sum sore of DC was 4.4 (3.5), tophi 6.6 (6.6), aggregates 9.3 (5.6), calprotectin 801 (525) µg/L, CRP 7 (14) mg/L and serum urate (SUA) 499 (77) μmol/L. Carotid examinations were performed in 122 (60.4%) of the patients. Significant correlations were found between the MSU depositions and the inflammatory markers as well as cIMT. The 27% patients with increased calprotectin had the highest levels of each of the three elementary lesions (p=0.001) (Figure), and the 39% with elevated CRP levels had the highest levels of tophi and aggregates (p<0.05). The 18% with increased thickness of cIMT and the 53% of patients with carotid plaque had the highest levels of aggregates (p=0.003 and p=0.037, respectively).Conclusion:In asymptomatic gout patients, higher load of MSU crystal depositions was associated with increased levels of inflammatory markers, cIMT and presence of atherosclerotic plaques in the carotid arteries. This may indicate that crystal depositions cause subclinical inflammation with subsequent systemic implications, but future longitudinal studies are needed to confirm such causal relationships.Sum scoredouble contourSum scoretophiSum score aggregatesCalprotectin0.26**0.32**0.28**CRP0.20*0.25**0.18*Right IMTNSNS0.18*Left IMTNSNS0.21*Sum bilateral IMTNSNS0.22*Spearman’s correlations. NS; Not significant, *p<0.05, **p<0.001Disclosure of Interests:Hilde Berner Hammer Speakers bureau: AbbVie, Lilly and Novartis, Silvia Rollefstad: None declared, Gro Jensen: None declared, Lars Karoliussen: None declared, Lene Terslev Speakers bureau: Speakers fee from AbbVie, Janssen, Roche, Novartis, Pfizer, MSD, BMS and GE, Espen A Haavardsholm: None declared, Tore K. Kvien Speakers bureau: Tore K Kvien has received fees for speaking and/or consulting and/or research funding to Diakonhjemmet Hospital from AbbVie, Biogen, BMS, Celltrion, Egis, Evapharma, Ewopharma, Eli Lilly, Gilead, Hikma, MSD, Mylan, Novartis, Oktal, Pfizer, Sandoz, Sanofi and UCB., Anne Grete Semb: None declared, Till Uhlig: None declared

Diagnostic efficacy of joint ultrasonography, dual-energy computed tomography and minimally invasive arthroscopy on knee gouty arthritis, a comparative study

Objective: This study aimed to investigate the diagnostic performance of minimally invasive arthroscopy for knee gout when comparing with joint ultrasonography and dual-energy computed tomography (DECT). Methods: From January 2016 to December 2018, 121 inpatients with knee joint swelling and pain were prospectively enrolled, including 63 gout patients and 58 non-gout patients. All patients underwent pre-operative ultrasonography and DECT to evaluate knee joint monosodium urate (MSU) deposits, followed by minimally invasive arthroscopy. The gold-standard for gout diagnosis was defined as the detection of MSU crystals in the synovial fluid under polarizing microscopic or pathological analysis. Results: The diagnostic results of ultrasonic double contour sign, hyperechogenic foci, MSU deposition (detected by DECT), MSU deposition (detected by arthroscopy) and MSU deposition in cartilage (detected by arthroscopy) were significantly associated with that of the gold-standard. Except for hyperechogenic foci, the other four indexes had high sensitivity and specificity (approximately or over 80%) and a large odds ratio (OR) (14.73 to 36.56), indicating good diagnostic performance. Detection of MSU deposition in cartilage by arthroscopy had a good diagnostic agreement with the ultrasonic double contour sign (κ = 0.711, p < 0.001). Conclusion: Joint ultrasonography, DECT, and minimally invasive arthroscopy had high sensitivity and specificity for the diagnosis of knee gouty arthritis. Minimally invasive arthroscopy was superior to joint ultrasonography and DECT, which can be a useful supplement for the diagnosis of gout. Advances in knowledge: This is the first study comparing the diagnostic performance for knee gout among the joint ultrasonography, DECT, and minimally invasive arthroscopy.

The trochanteric double contour is a valuable landmark for assessing femoral offset underestimation on standard radiographs: a retrospective study

Background Inaccurate projection on standard pelvic radiographs leads to the underestimation of femoral offset—a critical determinant of postoperative hip function—during total hip arthroplasty (THA) templating. We noted that the posteromedial facet of the greater trochanter and piriformis fossa form a double contour on radiographs, which may be valuable in determining the risk of underestimating femoral offset. We evaluate whether projection errors can be predicted based on the double contour width. Methods Plain anteroposterior (AP) pelvic radiographs and magnetic resonance images (MRIs) of 64 adult hips were evaluated retrospectively. Apparent femoral offset, apparent femoral head diameter and double contour widths were evaluated from the radiographs. X-ray projection errors were estimated by comparison to the true neck length measured on MRIs after calibration to the femoral heads. Multivariate analysis with backward elimination was used to detect associations between the double contour width and radiographic projection errors. Femoral offset underestimation below 10% was considered acceptable for templating. Results The narrowest width of the double line between the femoral neck and piriformis fossa is significantly associated with projection error. When double line widths exceed 5 mm, the risk of projection error greater than 10% is significantly increased compared to narrower double lines, and the acceptability rate for templating drops below 80% (p = 0.02). Conclusion The double contour width is a potential landmark for excluding pelvic AP radiographs unsuitable for THA templating due to inaccurate femoral rotation.

Performance of Ultrasound in the Clinical Evaluation of Gout and Hyperuricemia

BackgroundEvaluation of monosodium urate (MSU) crystal deposition and related lesion in joints using ultrasound in gout and hyperuricemia patients. MethodsTotal 202 gout patients and 43 asymptomatic hyperuricemia patients were included, the clinical data and ultrasunic assessment results were collected and statistically analyzed. ResultsDeposition of MSU crystals were found in 25.58% (11/43) of the patients with asymptomatic hyperuricemia and 76.24% (154/202) of the patients with gout. In the all examined 1082 joints from gout patients, 33.09% (358/1082) of them were detected MSU crystals. In MSU crystal positive joints, 77.37% (277/358) of them had history of attacks. Among the joints of gouty arthritis, 56.88% (277/487) of them were found MSU crystals. Double contour sign (DCS), hyperechoic aggregate (HAG) and Tophi were found in 32.65% (159/487), 7.80% (38/487) and 24.64% (120/487) of the joints, respectively. DCS and Tophi, but not HAG, appeared increasingly in gout duration extension. In the patients with more than 15 years of gout history, DCS, Tophi and HAG were found in 48.18%, 40.00%, 6.36% of US assessed joints, respectively. In the gout patients, synovial lesion and bone erosion were found in 17.74% (192/1082) and 7.58% (82/1082) of joints, respectively. Synovial lesion was related with HAG, while bone erosion was related to tophi and DCS. Nephrolithiasis was detected in 20.30% (41/202) of gout patients and 4.65% (2/43) of hyperuricemia patients, indicating nephrolithiasis occurred in more gout patients than in hyperuricemia patients.ConclusionHAG is the early sign of MSU crystal deposition in joints. Early urate lowering therapy (ULT) may reduce HAG and ameliorate synovitis and synovial hypertrophy. DCS and tophi are the risk factors of bone erosion. Early ULT should be considered in the gout patients with DCS or tophi. And nephrolithiasis was remarkably relevant to MSU crystal deposition in joints in gout patients.