Extracorporeal membrane oxygenation (ECMO) during aplasia: A bridge towards myopericarditis recovery after autologous hematopoietic stem cell transplant for systemic sclerosis and recent Coronarovirus disease (COVID-19) vaccination.

Systemic sclerosis (SSc) is a rare autoimmune disease (AD), characterised by early diffuse vasculopathy, activation of the immune response and progressive skin and internal organ fibrosis. In severe progressive diffuse SSc (dSSc), autologous hematopoietic stem cell transplantation (aHSCT) improves survival, despite its own risk of complications and transplant related mortality (TRM). We present herein the case of a dSSc patient undergoing aHSCT with low dose cyclophosphamide conditioning and sudden acute myopericarditis and cardiogenic shock, four weeks after a second mRNA SARS-CoV-2 vaccine (Pfizer) injection. Four days of extracorporeal membrane oxygenation (ECMO) support during the aplasia period, allowed to observe full cardiac function recovery and progressive SSc rehabilitation with sustained disease response at 30 months follow-up. This report illustrates, for the first time to our knowledge, that ECMO can be indicated despite aplasia during aHSCT and successfully used as a bridge towards heart function recovery in highly selected and fragile AD patients. We review the factors that may contribute to endothelial and myocardial stunning and acute reversible cardiac failure in SSc and aggravate intrinsic endothelial injury during the aHSCT procedure. These classically include: cyclophosphamide drug toxicity, viral infections and autoimmune activation with disease flair per se. In the COVID-19 pandemic times, acute myocarditis due to recent viral infection or mRNA vaccine per se, must also be considered.

In inflammatory myopathies, dropped head/bent spine syndrome is associated with scleromyositis: an international case-control study.

BACKGROUND: Some myopathies can lead to dropped head or bent spine syndrome (DH/BS). The significance of this symptom has not been studied in inflammatory myopathies (IM). OBJECTIVES: To assess the significance of DH/BS in patients with IM. METHODS: Practitioners from five IM networks were invited to report patients with IM suffering from DH/BS (without other known cause than IM). IM patients without DH/BS, randomly selected in each participating centre, were included as controls at a ratio of 2 to 1. RESULTS: 49 DH/BS-IM patients (DH: 57.1%, BS: 42.9%) were compared with 98 control-IM patients. DH/BS-IM patients were older (65 years vs 53 years, p<0.0001) and the diagnosis of IM was delayed (6 months vs 3 months, p=0.009). Weakness prevailing in the upper limbs (42.9% vs 15.3%), dysphagia (57.1% vs 25.5%), muscle atrophy (65.3% vs 34.7%), weight loss (61.2% vs 23.5%) and loss of the ability to walk (24.5% vs 5.1%) were hallmarks of DH/BS-IM (p≤0.0005), for which the patients more frequently received intravenous immunoglobulins (65.3% vs 34.7%, p=0.0004). Moreover, DH/BS-IM patients frequently featured signs and/or complications of systemic sclerosis (SSc), fulfilling the American College of Rheumatology/European Alliance of Associations for Rheumatology criteria for this disease in 40.8% of the cases (vs 5.1%, p<0.0001). Distribution of the myopathy, its severity and its association with SSc were independently associated with DH/BS (p<0.05). Mortality was higher in the DH/BS-IM patients and loss of walking ability was independently associated with survival (p<0.05). CONCLUSION: In IM patients, DH/BS is a marker of severity and is associated with SSc (scleromyositis).

Neurological outcomes in immune checkpoint inhibitor-related neurotoxicity.

While the spectrum of neurological immune checkpoint inhibitor-related adverse events is expanding, patients' outcomes are not well documented. This study aimed to assess outcomes of neurological immune-related adverse events and to identify prognostic factors. All patients experiencing grade ≥2 neurological immune-related adverse events identified at two clinical networks (French Reference Center for Paraneoplastic Neurological Syndromes, Lyon; and OncoNeuroTox, Paris) over five years were included. Modified Rankin scores were assessed at onset, 6, 12, 18 months, and last visit. A multi-state Markov model was used to estimate the transition rates between minor disability (mRS <3), severe disability (mRS 3-5), and death (mRS 6), over the study period. The state-to-state transition rates were estimated using maximum likelihood and variables were introduced into the different transitions to study their effects. A total of 147 patients were included out of 205 patients with a suspicion of neurological immune-related adverse events. The median age was 65 years (range 20-87) and 87/147 patients (59.2%) were male. Neurological immune-related adverse events involved the peripheral nervous system in 87/147 patients (59.2%), the central nervous system in 51/147 (34.7%), and both systems in 9/147 (6.1%). Paraneoplastic-like syndromes were observed in 30/147 patients (20.4%). Cancers included lung cancers (36.1%), melanoma (30.6%), urological cancers (15.6%), and others (17.8%). Patients were treated with programmed cell death protein (ligan) 1 (PD(L)1) inhibitors (70.1%), CTLA4 inhibitors (3.4%) or both (25.9%). Severe disability was reported in 108/144 patients (75.0%) at onset and in 33/146 patients (22.6%) at last visit (median follow-up duration: 12 months, range 0.5-50); 48/147 (32.7%) patients died, from cancer progression (17/48, 35.4%), neurological toxicity (15/48, 31.2%), other causes (10/48, 20.8%) or unknown causes (6/48, 12.5%). The rate of transition from severe to minor disability independently increased with melanoma [compared to lung cancer, hazard ratio = 3.26, 95%CI (1.27; 8.41)] and myositis/neuromuscular junction disorders [hazard ratio = 8.26, 95%CI (2.90; 23.58)], and decreased with older age [hazard ratio = 0.68, 95%CI (0.47; 0.99)] and paraneoplastic-like syndromes [hazard ratio = 0.29, 95%CI (0.09; 0.98)]. In patients with neurological immune-related adverse events, myositis/neuromuscular junction disorders and melanoma increase the transition rate from severe to minor disability, while older age and paraneoplastic-like syndromes result in poorer neurological outcomes; future studies are needed to optimize the management of such patients.

Efficacy of plasma exchange in patients with anti-MDA5 rapidly progressive interstitial lung disease.

BACKGROUND: Rapidly progressive interstitial lung disease (RP-ILD) is a frequent and severe manifestation of anti-MDA5 dermatomyositis (MDA5-DM) associated with poor outcome. The optimal treatment regimen for MDA5-DM RP-ILD is yet to be determined. Specifically, the value of adding plasma exchange (PLEX) to corticosteroids and immunosuppressants remains unclear. We aimed to evaluate the effect of PLEX on the outcome of patients with MDA5-DM RP-ILD. METHODS: This French nationwide multicentre retrospective study included all MDA5-DM RP-ILD patients from 2012 to 2021 admitted to 18 centres. The primary endpoint was one-year transplant-free survival. RESULTS: 51 patients with MDA5-DM RP-ILD (female 67%; mean age at disease onset: 51 ± 11.6 years) were included. Thirty-two (63%) patients required mechanical ventilation and twenty-five (49%) received PLEX. One-year mortality or lung transplant occurred in 63% cases after a median follow-up of 77 [38-264] days. The Cox proportional hazards multivariable model only retained mechanical ventilation but not PLEX (p = 0.7) as independent predictor of the primary endpoint. One-year transplant-free survival rates in PLEX + vs. PLEX-were 20% vs. 54% (p = 0.01), respectively. The Kaplan-Meier estimated probabilities of one-year transplant-free survival was statistically higher in PLEX-compared to PLEX + patients (p = 0.05). PLEX + compared to PLEX-patients more frequently received mechanical ventilation and immunosuppressants suggesting PLEX + patients had a more severe disease. CONCLUSION: MDA5-DM RP-ILD is associated with poor rate of one-year transplant-free survival. The use of PLEX was not associated with a better outcome albeit they were mainly given to more severe patients. While our study reports the largest series of MDA5-DM RP-ILD given PLEX, these results needs to be interpreted with caution owing the numerous selection, indication and interpretation bias. Further studies are needed to evaluate their efficacy in this setting.

Lung transplantation for interstitial lung disease in idiopathic inflammatory myositis: A cohort study.

In patients with interstitial lung disease (ILD) complicating classical or amyopathic idiopathic inflammatory myopathy (IIM), lung transplantation outcomes might be affected by the disease and treatments. Here, our objective was to assess survival and prognostic factors in lung transplant recipients with IIM-ILD. We retrospectively reviewed data for 64 patients who underwent lung transplantation between 2009 and 2021 at 19 European centers. Patient survival was the primary outcome. At transplantation, the median age was 53 [46-59] years, 35 (55%) patients were male, 31 (48%) had classical IIM, 25 (39%) had rapidly progressive ILD, and 21 (33%) were in a high-priority transplant allocation program. Survival rates after 1, 3, and 5 years were 78%, 73%, and 70%, respectively. During follow-up (median, 33 [7-63] months), 23% of patients developed chronic lung allograft dysfunction. Compared to amyopathic IIM, classical IIM was characterized by longer disease duration, higher-intensity immunosuppression before transplantation, and significantly worse posttransplantation survival. Five (8%) patients had a clinical IIM relapse, with mild manifestations. No patient experienced ILD recurrence in the allograft. Posttransplantation survival in IIM-ILD was similar to that in international all-cause-transplantation registries. The main factor associated with worse survival was a history of muscle involvement (classical IIM). In lung transplant recipients with idiopathic inflammatory myopathy, survival was similar to that in all-cause transplantation and was worse in patients with muscle involvement compared to those with the amyopathic disease.

Skeletal muscle provides the immunological micro-milieu for specific plasma cells in anti-synthetase syndrome-associated myositis.

Anti-synthetase syndrome (ASyS)-associated myositis is a major subgroup of the idiopathic inflammatory myopathies (IIM) and is characterized by disease chronicity with musculoskeletal, dermatological and pulmonary manifestations. One of eight autoantibodies against the aminoacyl-transferase RNA synthetases (ARS) is detectable in the serum of affected patients. However, disease-specific therapeutic approaches have not yet been established.To obtain a deeper understanding of the underlying pathogenesis and to identify putative therapeutic targets, we comparatively investigated the most common forms of ASyS associated with anti-PL-7, anti-PL-12 and anti-Jo-1. Our cohort consisted of 80 ASyS patients as well as healthy controls (n = 40), diseased controls (n = 40) and non-diseased controls (n = 20). We detected a reduced extent of necrosis and regeneration in muscle biopsies from PL-12+ patients compared to Jo-1+ patients, while PL-7+ patients had higher capillary dropout in biopsies of skeletal muscle. Aside from these subtle alterations, no significant differences between ASyS subgroups were observed. Interestingly, a tissue-specific subpopulation of CD138+ plasma cells and CXCL12+/CXCL13+CD20+ B cells common to ASyS myositis were identified. These cells were localized in the endomysium associated with alkaline phosphatase+ activated mesenchymal fibroblasts and CD68+MHC-II+CD169+ macrophages. An MHC-I+ and MHC-II+ MxA negative type II interferon-driven milieu of myofiber activation, topographically restricted to the perifascicular area and the adjacent perimysium, as well as perimysial clusters of T follicular helper cells defined an extra-medullary immunological niche for plasma cells and activated B cells. Consistent with this, proteomic analyses of muscle tissues from ASyS patients demonstrated alterations in antigen processing and presentation. In-depth immunological analyses of peripheral blood supported a B-cell/plasma-cell-driven pathology with a shift towards immature B cells, an increase of B-cell-related cytokines and chemokines, and activation of the complement system. We hypothesize that a B-cell-driven pathology with the presence and persistence of a specific subtype of plasma cells in the skeletal muscle is crucially involved in the self-perpetuating chronicity of ASyS myositis. This work provides the conceptual framework for the application of plasma-cell-targeting therapies in ASyS myositis.

Remdesivir in combination with dexamethasone for patients hospitalized with COVID-19: A retrospective multicenter study.

BACKGROUND: Dexamethasone is standard of care for the treatment of patients with COVID-19 requiring oxygen. The objective is to assess the clinical benefit of adding remdesivir to dexamethasone. PATIENTS AND METHODS: A retrospective cohort study of hospitalized patients with COVID-19 pneumonia requesting low-flow oxygen who received dexamethasone. Patients admitted to infectious diseases wards also received remdesivir. Primary outcome was duration of hospitalization after oxygen initiation. Secondary outcomes were in-hospital death, and death and/or transfer to the intensive care unit. To handle potential confounding by indication bias, outcome comparison was performed on propensity score-matched populations. Propensity score was estimated by a multivariable logistic model including prognostic covariates; then 1:1 matching was performed without replacement, using the nearest neighbor algorithm with a caliper of 0.10 fold the standard deviation of the propensity score as the maximal distance. Balance after matching was checked on standardized mean differences. RESULTS: From August 15th 2020, to February 28th, 2021, 325 patients were included, 101 of whom received remdesivir. At admission median time from symptoms onset was 7 days, median age: 68 years, male sex; 61%, >1 comorbidity: 58.5%. Overall 180 patients matched on propensity score were analyzed, 90 each received remdesivir plus dexamethasone or dexamethasone alone. Median duration of hospitalization was 9 (IQR: 7-13) and 9 (IQR: 5-18) days with and without remdesivir, respectively (p = 0.37). In-hospital death rates and rates of transfer to the intensive care unit or death were 8.9 and 17.8% (HR: 0.46, 95% CI: 0.21-1.02, p = 0.06) and 20.0 and 35.6% with and without remdesivir, respectively (HR: 0.45, 95% CI: 0.23-0.89, p = 0.015). CONCLUSION: In hospitalized patients with COVID-19 pneumonia receiving low-flow oxygen and dexamethasone, the addition of remdesivir was not associated with shorter hospitalization or lower in-hospital mortality but may have reduced the combined outcome of death and transfer to the intensive care unit.

Anti-PD-1 immune-related adverse events are associated with high therapeutic antibody fixation on T cells.

Immune checkpoint inhibitors (ICI) widely improved the treatment of solid and hematologic malignancies. Yet, a remarkable proportion of patients receiving ICI develop immune related adverse events (irAEs) which are difficult to define as treatment-related. This underlines the need to develop a biomarker to guide irAE diagnosis. We developed a novel flow cytometry assay combining measurement of anti-PD-1 (programmed cell death protein-1) occupancy and evaluation of remaining PD-1 receptor availability with anti-IgG4 PE and anti-PD-1 BV421. We prospectively collected blood and biological fluids samples from patients treated by IgG4 anti-PD-1 therapy (nivolumab or pembrolizumab), with (n=18) or without (n=12) current irAE. We analyzed PD-1+ and IgG4+ staining pattern and MFI values of these parameters on CD4 and CD8 T cells, and IgG4+/PD-1+ MFI ratios are calculated. A higher mean fluorescence intensity IgG4+/PD-1+ ratio was measured on peripheral CD4+ T cells of irAE cases, when compared to controls (p=0.003). ICI-related toxicity is therefore associated with increased therapeutic antibody occupancy of PD-1 receptors on CD4+ T cells. Furthermore, in one case of ICI-related pneumonitis, binding of therapeutic antibody was stronger on lung CD4+ T cell than in blood. In another case of ICI-related encephalitis, the PD-1 receptor occupancy was total on CSF CD4 T cells, but only partial on peripherical CD4 T cells. Our results suggest that flow cytometry monitoring of ICI occupancy can be used in patients treated with monoclonal ICI to guide irAE diagnosis.

Significance of Sjögren's syndrome and anti-cN1A antibody in myositis patients.

OBJECTIVE: We recently recorded a high prevalence of inclusion body myositis (IBM) in patients with Sjögren's syndrome (SS). Whether myositis patients with SS differ from myositis patients without SS in terms of the characteristics of the myositis is currently unknown. Anti-cytosolic 5'-nucleotidase 1 A (cN1A) has recently been proposed as a biomarker for IBM but is also frequent in SS. Whether anti-cN1A is independently associated with IBM is still an open question. We aimed to assess the significance of SS and anti-cN1A in myositis patients. METHODS: Cumulative data on all myositis patients (EULAR/ACR 2017 criteria) screened for SS (ACR/EULAR 2016 criteria) in a single centre were analysed. Ninety-nine patients were included, covering the whole spectrum of EULAR/ACR 2017 myositis subgroups and with a median follow-up of 6 years (range 1.0-37.5). The 34 myositis patients with SS (myositis/SS+) were compared with the 65 myositis patients without SS (myositis/SS-). RESULTS: . IBM was present in 24% of the myositis/SS+ patients vs 6% of the myositis/SS- group (P = 0.020). None of the IBM patients responded to treatment, whether they had SS or not. Anti-cN1A was more frequent in myositis/SS+ patients (38% vs 6%, P = 0.0005), independently of the higher prevalence of IBM in this group (multivariate P value: 0.02). Anti-cN1A antibody specificity for IBM was 0.96 (95% CI: 0.87, 0.99) in the myositis/SS- group but dropped to 0.70 (95% CI: 0.48, 0.85) in the myositis/SS+ group. INTERPRETATION: In myositis patients, SS is associated with IBM and with anti-cN1A antibodies, independently of the IBM diagnosis. As a consequence, anti-cN1A has limited specificity for IBM in myositis patients with SS.

Increased Concentrations of Circulating Soluble MHC Class I-Related Chain A (sMICA) and sMICB and Modulation of Plasma Membrane MICA Expression: Potential Mechanisms and Correlation With Natural Killer Cell Activity in Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is a severe autoimmune disease of unknown etiology. The major histocompatibility complex (MHC) class I-related chain A (MICA) and B (MICB) are stress-inducible cell surface molecules. MICA and MICB label malfunctioning cells for their recognition by cytotoxic lymphocytes such as natural killer (NK) cells. Alterations in this recognition have been found in SLE. MICA/MICB can be shed from the cell surface, subsequently acting either as a soluble decoy receptor (sMICA/sMICB) or in CD4+ T-cell expansion. Conversely, NK cells are frequently defective in SLE and lower NK cell numbers have been reported in patients with active SLE. However, these cells are also thought to exert regulatory functions and to prevent autoimmunity. We therefore investigated whether, and how, plasma membrane and soluble MICA/B are modulated in SLE and whether they influence NK cell activity, in order to better understand how MICA/B may participate in disease development. We report significantly elevated concentrations of circulating sMICA/B in SLE patients compared with healthy individuals or a control patient group. In SLE patients, sMICA concentrations were significantly higher in patients positive for anti-SSB and anti-RNP autoantibodies. In order to study the mechanism and the potential source of sMICA, we analyzed circulating sMICA concentration in Behcet patients before and after interferon (IFN)-α therapy: no modulation was observed, suggesting that IFN-α is not intrinsically crucial for sMICA release in vivo. We also show that monocytes and neutrophils stimulated in vitro with cytokines or extracellular chromatin up-regulate plasma membrane MICA expression, without releasing sMICA. Importantly, in peripheral blood mononuclear cells from healthy individuals stimulated in vitro by cell-free chromatin, NK cells up-regulate CD69 and CD107 in a monocyte-dependent manner and at least partly via MICA-NKG2D interaction, whereas NK cells were exhausted in SLE patients. In conclusion, sMICA concentrations are elevated in SLE patients, whereas plasma membrane MICA is up-regulated in response to some lupus stimuli and triggers NK cell activation. Those results suggest the requirement for a tight control in vivo and highlight the complex role of the MICA/sMICA system in SLE.

Treatment strategies and safety of rechallenge in the setting of immune checkpoint inhibitors-related myositis: a national multicentre study.

OBJECTIVES: The occurrence of immune-related myositis (irM) is increasing, yet there are no therapeutic guidelines. We sought to analyse the current therapeutic strategies of irM and evaluate the outcomes of immune checkpoint inhibitors (ICIs) rechallenge. METHODS: We conducted a nationwide retrospective study between April 2018 and March 2020 including irM without myocardial involvement. Depending on the presence of cutaneous signs or unusual histopathological features, patients were classified into two groups: typical or atypical irM. Therapeutic strategies were analysed in both groups. The modalities and outcomes of ICI rechallenge were reviewed. RESULTS: Among the 20 patients, 16 presented typical irM. Regardless of severity, most typical irM were treated with steroid monotherapy (n = 14/16) and all had a complete response within ≤3 weeks. The efficacy of oral steroids for non-severe typical irM (n = 10) was the same with low-dose (≤0.5 mg/kg/day) or high-dose (1 mg/kg/day). Severe typical irM were successfully treated with intravenous methylprednisolone. Atypical irM (n = 4) had a less favourable evolution, including one irM-related death, and required heavy immunosuppression. ICIs were safely reintroduced in nine patients presenting a moderate (n = 6) or a severe (n = 3) irM. CONCLUSION: Our data highlight that steroid monotherapy is an effective treatment for typical irM, either with prednisone or with intravenous methylprednisone pulses depending on the severity. The identification of unusual features is important in determining the initial therapeutic strategy. The outcomes of rechallenged patients are in favour of a safe reintroduction of ICI following symptom resolution and creatin kinase (CK) normalization in moderate and severe forms of irM.

Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial.

BACKGROUND: Inclusion body myositis is the most frequent myositis in patients older than 50 years. Classical immunosuppressants are ineffective in treating inclusion body myositis, and to date there are no recommendations for pharmacological approaches to treatment. When used after organ transplantation, sirolimus can block the proliferation of effector T cells, while preserving T regulatory cells, and induce autophagy, all of which are processes that are impaired in inclusion body myositis. In this pilot study, we aimed to test the efficacy of sirolimus in patients with inclusion body myositis. METHODS: This randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial was done at a single hospital in Paris, France. The study included men and women (aged 45-80 years) who had a defined diagnosis of inclusion body myositis according to established criteria. Eligible participants were randomly assigned (1:1) to receive once-daily oral sirolimus 2 mg or placebo. Centralised balanced block randomisation (blocks of four) was computer generated without stratification. The study comprised a 15-day screening period (days -15 to 0) and a 52-week treatment period (day 0 to month 12). The primary endpoint was the relative percentage change from baseline to month 12 in maximal voluntary isometric knee extension strength. Secondary endpoints included the following assessments at months 6 and 12: 6-min walking distance, isometric muscle strength for hand grip (finger flexors), knee flexion and elbow flexion and extension, forced vital capacity, muscle replacement with fat measured by quantitative nuclear MRI, Inclusion Body Myositis Weakness Composite Index (IBMWCI), Inclusion Body Myositis Functional Rating Scale (IBMFRS), Health Assessment Questionnaire without Disability Index (HAQ-DI), and analyses of T-cell subpopulations by mass cytometry. The primary analysis was done on the intention-to-treat population. The trial is registered at ClinicalTrials.gov, NCT02481453. FINDINGS: Between July 15, 2015, and May 13, 2016, we screened 285 patients, 44 of whom were randomly allocated to sirolimus (22 patients) or placebo (22 patients). We observed no difference in the primary outcome of relative percentage change from baseline to month 12 of the maximal voluntary isometric knee extension strength (median difference 3·78, 95% CI -10·61 to 17·31; p=0·85). For secondary outcomes, differences between the groups were not significant for changes in strength of other muscle groups (grip, elbow flexion and extension, or knee flexion), IBMWCI, IBMFRS, and lower limb muscle fat fraction. However, we observed significant differences in favour of sirolimus between the study groups for HAQ-DI, forced vital capacity, thigh fat fraction, and 6-min walking distance. Ten (45%) of 22 patients in the sirolimus group had a serious adverse event compared with six (27%) of 22 patients in the placebo group. Four (18%) patients in the sirolimus group stopped their treatment because of adverse events (severe mouth ulcers, aseptic pneumonia, renal insufficiency, and peripheral lower limb oedema), which resolved after treatment discontinuation. Canker sores were the most frequent side-effect and were mainly mild or moderate in ten patients. INTERPRETATION: We found no evidence for efficacy of sirolimus for treating inclusion body myositis based on maximal voluntary isometric knee extension strength and other muscle strength measures, and the side-effects of treatment were substantial for some patients. However, we believe there was enough evidence of benefit in certain secondary outcomes to pursue a multicentre phase 3 trial to further assess the safety and efficacy of sirolimus. FUNDING: Institut national de la santé et de la recherche médicale, Direction générale de l'offre de soins, and Association Française contre les Myopathies.

Relationship between change in physical activity and in clinical status in patients with idiopathic inflammatory myopathy: A prospective cohort study.

OBJECTIVE: This study aimed to investigate the relationship between changes in clinical status on daily life physical activity (PA) in patients with idiopathic inflammatory myopathy (IIM). METHODS: Patients with dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM) or overlap myositis (OM) who presented either a new-onset or relapsing IIM, stable disease on maintenance therapy or were undergoing immunosuppressant tapering were included. Patients were evaluated at inclusion (V0), and at two follow-up visits (V1, 94±12 days from V0; V2, 96±17 days from V1). The American College of Rheumatology/European League against Rheumatism (ACR/EULAR) response criteria was recorded. PA assessed using 14-days raw accelerometry data gathered using a wrist-worn accelerometer after each visit (mean daily Euclidean norm minus 1 g (ENMO) was computed). RESULTS: Fifty-five patients (16 OM, 27 IMNM and 12 DM) were included. At baseline, 67% of patients had an ENMO Z-score less than 1. At inclusion, ENMO mainly correlated with health assessment questionnaire score (HAQ, ρ=-0.51, p<0.01), manual muscle testing 8 (MMT8, ρ=0.42, p<0.01), creatinine level (ρ=0.41, p<0.01), and SF-36 physical functioning score (ρ=0.38, p<0.002). At follow-up, ENMO changes mainly correlated with changes in MMT8, HAQ, SF-36 fatigue, and depression score (all ρ>0.43, all p<0.001). Level of agreement between ACR/EULAR response criteria and changes in PA was 15, 45, and 90% for minimal (n = 13), moderate (n = 20), and major (n = 10) improvements, respectively. CONCLUSION: Baseline PA levels and change in PA correlated with muscle strength and function, yet changes in PA were also influenced by psychological status. Only patients with major improvements on the ACR/EULAR criteria had significant increase in PA. Accelerometer may serve as an objective tool to define a clinically relevant real-life outcome.