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Antibiotic-Refractory Lyme Arthritis (ARLA) involves a complex interplay of T cell responses targeting Borrelia burgdorferi antigens succeeding towards autoantigens by epitope spreading. However, the precise molecular mechanisms driving the pathogenic T cell response in ARLA remain unclear. Our aim was to elucidate the molecular program of disease-specific Th cells. Using flow cytometry, high-throughput T cell receptor (TCR) sequencing and scRNA-seq of CD4+ Th cells isolated from the joints of European ARLA patients, we aimed at inferring antigen specificity through unbiased analysis of TCR repertoire patterns, identifying surrogate markers for disease-specific TCRs and connecting TCR specificity to transcriptional patterns. PD-1hiHLA-DR+CD4+ effector T cells were clonally expanded within the inflamed joints and persisted throughout disease course. Among these cells, we identified a distinct TCRβ motif restricted to HLA-DRB1*11 or *13 alleles. These alleles, being underrepresented in North American ARLA patients, were unexpectedly prevalent in our European cohort. The identified TCRβ motif served as surrogate marker for a convergent TCR response specific to ARLA, distinguishing it from other rheumatic diseases. In the scRNA-seq dataset, the TCRβ motif particularly mapped to peripheral T helper (TPH) cells displaying signs of sustained proliferation, continuous TCR signaling, and expressing CXCL13 and IFN-γ. By inferring disease-specific TCRs from synovial T cells we identified a convergent TCR response in the joints of ARLA patients that continuously fueled the expansion of TPH cells expressing a pathogenic cytokine effector program. The identified TCRs will aid in uncovering the major antigen targets of the maladaptive immune response. Supported by the German Research Foundation (DFG) MO 2160/4-1; the Federal Ministry of Education and Research (BMBF; Advanced Clinician Scientist-Program INTERACT; 01EO2108) embedded in the Interdisciplinary Center for Clinical Research (IZKF) of the University Hospital Würzburg; the German Center for Infection Research (DZIF; Clinical Leave Program; TI07.001_007) and the Interdisciplinary Center for Clinical Research (IZKF) Würzburg (Clinician Scientist Program, Z-2/CSP-30).

Objective To assess the first-year features of patients with chronic nonbacterial osteomyelitis (CNO). Methods Patients with a diagnosis of CNO, disease duration of under 13 months, and first registration in the German National Pediatric Rheumatologic Database (NPRD) between 2009 and 2018 were included in this cross-sectional analysis. Results Of 774 documented patients, 62.8% were female, and all patients had a median age of 11 years. The most affected clinical sites were the tibia (29.7%), pelvis (28.0%), and femur (27.8%). HLA-B27 was positive in 48 of 314 analyzed patients (15.3%). In 406 patients, an X-ray was performed at the first visit; X-ray results showed osteosclerosis/−lysis in 34.0% and hyperostosis in 14.5% of the patients. MRI scans (focal and whole-body scans) were performed in 648 patients, and 81.5% showed a positive TIRM/STIR signal. A total of 84.7% of the patients were administered nonsteroidal anti-inflammatory drugs, 9.6% were administered oral glucocorticoids, 10.8% were administered disease-modifying anti-rheumatic drugs (DMARDs), and 6.1% were administered bisphosphonates. An evaluation of the patient’s questionnaire showed an overall well-being (NRS 0–10) of 2.0. The PedCNO disease “activity” score revealed a 70% improvement in variables in 43% of patients in the initial 1-year follow-up. Copresentation with diagnostic criteria of pediatric enthesitis-related arthritis was rare. Conclusion To our knowledge, the NPRD cohort seemed to be the largest cohort of children and adolescents suffering from CNO worldwide. Most patients were treated effectively with NSAIDs, and only a small group of patients was administered additional medication. The patient-defined measures of disease activity had a moderate impact on patients’ daily lives. Trial registration Not applicable.

Background This prospective, long-term observational study, initiated in 2002, aimed to characterize clinical and laboratory data, whole body MRI detected lesions, and treatment responses in 37 juvenile patients with chronic non-bacterial osteomyelitis at a time when biological DMARDs were not yet standard therapy. Methods Patients were assessed at baseline and at 1 (without MRI), 3, 6, 12, 18, 24, 36, 48, 60 months. All patients received naproxen as first-line therapy. Clinical management allowed for escalation to sulfasalazine, pamidronate, and glucocorticoids as needed. Treatment response was evaluated using the pedCNO disease activity score (30/50/70/90% improvement). Further composite numeric disease activity (DA) scores– the CARRA CDAS and a new MRI DAS - were applied. Results The mean age at disease onset was 10.8 years, with a diagnostic delay of 5.8 months. Naproxen was the initial treatment in all patients. Second-line therapy was initiated in 10 patients due to inadequate improvement in physician global assessment of disease activity, patient-reported overall wellbeing or MRI lesions. Escalated therapies included sulfasalazine ( n  = 10), bisphosphonates ( n  = 1), methotrexate ( n  = 1), and short- (< 4 wks) or long-term oral glucocorticoids ( n  = 5 and n  = 3, respectively). The mean number of clinical lesions decreased from 2.1 to 0.4 at 12 months and reached 0.15 at 60 months. MRI-detected lesions declined from 5.0 to 2.25 at 12 months and to 1.1 at 60 months. Conclusion Most children experienced favourable long-term outcomes. Clinical improvement occurred more rapidly than radiologic resolution. Patients with insufficient response to NSAIDs should be considered for a treat-to-target approach, including the use of conventional and biologic DMARDs. Trial registration A trial registration EUDRA CT was not available at the time the study was started. Informed consent was given by all parents.

Background Hypophosphatasia (HPP) is a rare, inherited metabolic disorder caused by loss-of-function mutations in the ALPL gene that encodes the tissue-nonspecific alkaline phosphatase TNAP (ORPHA 436). Its clinical presentation is highly heterogeneous with a remarkably wide-ranging severity. HPP affects patients of all ages. In children HPP-related musculoskeletal symptoms may mimic rheumatologic conditions and diagnosis is often difficult and delayed. To improve the understanding of HPP in children and in order to shorten the diagnostic time span in the future we studied the natural history of the disease in our large cohort of pediatric patients. This single centre retrospective chart review included longitudinal data from 50 patients with HPP diagnosed and followed at the University Children’s Hospital Wuerzburg, Germany over the last 25 years. Results The cohort comprises 4 (8%) perinatal, 17 (34%) infantile and 29 (58%) childhood onset HPP patients. Two patients were deceased at the time of data collection. Diagnosis was based on available characteristic clinical symptoms (in 88%), low alkaline phosphatase (AP) activity (in 96%), accumulating substrates of AP (in 58%) and X-ray findings (in 48%). Genetic analysis was performed in 48 patients (31 compound heterozygous, 15 heterozygous, 2 homozygous mutations per patient), allowing investigations on genotype-phenotype correlations. Based on anamnestic data, median age at first clinical symptoms was 3.5 months (min. 0, max. 107), while median time to diagnosis was 13 months (min. 0, max. 103). Common symptoms included: impairment of motor skills (78%), impairment of mineralization (72%), premature loss of teeth (64%), musculoskeletal pain and craniosynostosis (each 64%) and failure to thrive (62%). Up to now 20 patients started medical treatment with Asfotase alfa. Conclusions Reported findings support the clinical perception of HPP being a chronic multi-systemic disease with often delayed diagnosis. Our natural history information provides detailed insights into the prevalence of different symptoms, which can help to improve and shorten diagnostics and thereby lead to an optimised medical care, especially with promising therapeutic options such as enzyme-replacement-therapy with Asfotase alfa in mind.

Hypophosphatasia (HPP) is a clinically heterogeneous rare, inherited disorder of bone and mineral metabolism with extensive allelic heterogeneity in the ALPL gene. In this report, we present a family with heterozygous parents (maternal p.(Glu191Lys), paternal p.(Gly334Asp) mutations in the ALPL gene) and four children (one genotypically normal, one heterozygous carrier and two compound heterozygous) showing an unexpected high phenotypic variability. One of the compound heterozygous showed clinical symptoms of the mild childhood form mainly affecting the teeth. The other one was more seriously affected with severe failure to thrive, delayed motor development, need for oxygen supply and profound mineralization deficit compatible with an infantile form of HPP. Functional in vitro studies identified p.(Glu191Lys) as mild (68%, no dominant-negative effect) and p.(Gly334Asp) as severely affected allele (1.2%, dominant-negative effect). In vitro simulation of the children's genetic status showed a residual AP activity of 29%, while the biochemical AP activity in the serum was comparably reduced in both children (22 and 36 U/l). This family report indicates that mapping ALPL mutations within the gene does not necessarily help to predict the clinical severity of the phenotype. Therefore, results of prenatal diagnostics have to be interpreted with caution and prenatal genetic diagnosis and counseling for HPP should be provided within an experienced multidisciplinary team. Research about other confounding factors is urgently needed.

Introduction Chronic non-bacterial osteomyelitis (CNO) is an autoinflammatory bone-disease of unknown origin. The National Pediatric Rheumatologic Database (NPRD) collects long-term data of children and adolescents with rheumatic diseases including CNO. Objective To assess characteristics, courses, and outcomes of CNO with onset in childhood and adolescence and to identify outcome predictors. Methods From 2015 to 2021 patients with a confirmed diagnosis of CNO, who were registered in the NPRD during their first year of disease and at least one follow-up visit, were included in this analysis and observed for up to 4 years. Results Four hundred patients with recent diagnosis of CNO were enrolled in the NRPD during the study period. After 4 years, patient data documentation was sufficient to be analyzed in 81 patients. A significant decline of clinical and radiological lesions is reported: at inclusion in the registry, the mean number of clinical lesions was 2.0 and 3.0 MRI lesions per patient. A significant decrease of manifestations during 4 years of follow-up (mean clinical lesions 0.5, p  < 0.001; mean MRI lesions 0.9 ( p  < 0.001)) was documented. A significant improvement of physician global disease activity (PGDA), patient-reported overall well-being, and childhood health assessment questionnaire (C-HAQ) was documented. Therapeutically, an increase of disease-modifying anti-rheumatic drugs over the years can be stated, while bisphosphonates rather seem to be considered as a therapeutic DMARD option in the first years of disease. Only 5–7% of the patients had a severe disease course as defined by a PGDA >  = 4. Predictors associated with a severe disease course include the site of inflammation (pelvis, lower extremity, clavicle), increased erythrocyte sedimentation rate, and multifocal disease at first documentation. The previously published composite PedCNO disease activity score was analyzed revealing a PedCNO70 in 55% of the patients at 4YFU. Conclusion An improvement of physician global disease activity (PGDA), patient reported overall well-being and imaging-defined disease activity measures was documented, suggesting that inactivity of CNO disease can be reached. PedCNO score and especially PGDA, MRI-defined lesions and in a number of patients also the C-HAQ seem to be reliable parameters for describing disease activity. The identification of risk factors at the beginning of the disease might influence treatment decision in the future.

Sterile bone inflammation is the hallmark of autoinflammatory bone disorders, including chronic nonbacterial osteomyelitis (CNO) with its most severe form chronic recurrent multifocal osteomyelitis (CRMO). Autoinflammatory osteopathies are the result of a dysregulated innate immune system, resulting in immune cell infiltration of the bone and subsequent osteoclast differentiation and activation. Interestingly, autoinflammatory bone disorders are associated with inflammation of the skin and/or the intestine. In several monogenic autoinflammatory bone disorders mutations in disease-causing genes have been reported. However, regardless of recent developments, the molecular pathogenesis of CNO/CRMO remains unclear. Here, we discuss the clinical presentation and molecular pathophysiology of human autoinflammatory osteopathies and animal models with special focus on CNO/CRMO. Treatment options in monogenic autoinflammatory bone disorders and CRMO will be illustrated.

BackgroundChronic non-bacterial osteomyelitis (CNO) is an autoinflammatory bone disorder affecting children and adolescents. Previously classified as a rare disease, recent studies suggest a higher incidence of the disease. CNO may develop into the clinical presentation of chronic recurrent osteomyelitis (CRMO) with high relapse rate and multifocality.Main bodyDiagnosis of CNO/CRMO is often delayed, with implications for disease severity and relapse rate. This can be significantly improved by knowledge of the disease entity and its characteristics. Imaging plays a key role in diagnosis, differential diagnosis and therapy monitoring. Magnetic resonance imaging (MRI) has several advantages compared to other imaging methods and is increasingly applied in clinical studies. Recent studies show that a whole-body (WB) coverage (WB-MRI) without contrast agent administration is a rational approach. This educational review is based on a systematic analysis of international peer-reviewed articles and presents our own clinical experiences. It provides an overview of disease entity, incidence and clinical diagnosis. The role of imaging, especially of whole-body MRI, is discussed in detail. Finally, practical advice for imaging, including flowcharts explaining when and how to apply imaging, is provided.ConclusionKnowing the specifics of CNO/CRMO and the importance of MRI/whole-body MRI allows rapid and efficient diagnosis as well as therapy support and helps to avoid irreversible secondary damage.

Chronic non-bacterial osteomyelitis (CNO) is the most common autoinflammatory bone disease in children and adolescents. This study investigated the progression of CNO lesions during therapy and the potential impact of sarcopenia on disease progression, utilizing routine MRI. A retrospective analysis of MRI examinations was conducted on 29 children and adolescents with CNO. CNO lesions were segmented. Sarcopenia was assessed using the total psoas muscle index (PMI) at lumbar vertebral levels L3/4 and L4/5. Measurements were taken at four time points during the disease course (T1: baseline, T2-T4: follow-up). Based on the PMI, patients were classified as sarcopenic or non-sarcopenic, and the progression of CNO lesions and the impact of sarcopenia were analyzed. A total of 29 patients, aged 1-16 years, were included in the study, with 13 males and 16 females. Patients with sarcopenia had a significantly larger mean lesion area (868.95 mm , SD = 684.49) compared to those without sarcopenia (636.11 mm , SD = 832.41); p = 0.042, d = 0.4). The comparison between the two patient groups revealed a consistently lower percentage reduction in lesion size for the sarcopenic patients at all time points. Notably, the difference between T1 and T3 was statistically significant (p = 0.045, d = 0.82). The present study indicates that sarcopenia may serve as a negative prognostic factor in the treatment of CNO. Incorporating sarcopenia assessment as an additional parameter in routine whole-body MRI examinations could enhance the evaluation process. Sarcopenia can be assessed using routine whole-body MRI in patients with CNO and may serve as a negative prognostic factor, potentially enhancing the evaluation process. Whole-body MRI is crucial for diagnosing and monitoring CNO. Routine whole-body MRI in CNO patients can also be used to assess sarcopenia as an additional parameter. Sarcopenia may act as a negative prognostic factor in CNO treatment, potentially improving the evaluation process.

Background Children and adolescents with juvenile idiopathic arthritis (JIA) are at increased risk for long-term physical and psychosocial complications, making physical activity (PA) and sedentary behaviour (SB) key modifiable lifestyle factors. Although increasingly acknowledged as relevant, data on the daily distribution of these behaviours in JIA remain scarce. This study aimed to (1) describe the time-use composition of SB and PA intensities in young people with JIA, (2) identify correlates of greater relative time spent in SB, and (3) compare movement behaviour patterns to matched population controls using a compositional data analysis (CoDA) approach. Methods Patients aged 10–20 years with JIA and individually matched population controls wore hip-worn accelerometers (ActiGraph wGT3X-BT) for eight consecutive days. Movement behaviours were categorized into SB, light-intensity PA, and moderate-to-vigorous PA (MVPA) using validated, age-specific cut-points. CoDA with log-ratio transformations was used to model associations and compare groups. Diifferences in movement composition were assessed using adjusted multivariate analysis of variance (MANOVA). Results Data from 126 matched pairs (mean age: 15.0 ± 2.1 years; 67% female) were analysed. Patients spent, on average, 86% of waking time in SB, 8% in light-intensity PA, and 6% in MVPA. Overall, 76% did not meet the WHO recommendation of an average of ≥ 60 min of MVPA per day. Among those who did, 87% still spent ≥ 75% of their wear time sedentary. A greater proportion of SB relative to PA was associated with female gender (B = 0.13; p  = 0.042), higher age (B = 0.06; p  < 0.001), and higher BMI (B = 0.01; p  = 0.049). Compared to controls, patients spent more time in SB, less in light-intensity PA, and slightly more in vigorous PA (all p  < 0.001). Group differences remained significant after adjustment and were consistent across weekdays and weekends. Conclusions Young people with well-controlled JIA show a distinctly unbalanced movement behaviour composition compared to controls, marked by a predominance of sedentary behaviour—even among those meeting PA guidelines. This highlights the limitations of threshold-based definitions and underscores the importance of assessing full daily movement patterns. Promoting light-intensity PA may offer a feasible strategy to reduce sedentary time, particularly in girls, older adolescents, and individuals with higher BMI. Trial registration The study was registered in the German Clinical Trials Register (DRKS00022258).