Sarcopenia, a progressive and generalized skeletal muscle disorder characterized by the accelerated loss of muscle mass and function, is associated with increased adverse outcomes such as falls, functional decline, frailty, and mortality (1).

At present, there is no universally accepted operational definition of sarcopenia. However, the proposals published by the European Working Group on Sarcopenia in Older People (EWGSOP), first in 2010 (EWGSOP-1) (2) and subsequently in 2019 (EWGSOP-2) (3), remain the predominant criteria in use. These frameworks advocate for a sequential diagnostic strategy, despite employing different criteria (4). Specifically, EWGSOP-1 defines sarcopenia through the concurrent observation of low muscle mass and diminished muscle function, indicated by reduced muscle strength or compromised physical performance. In contrast, EWGSOP-2 defines sarcopenia by combining low muscle mass and strength, using physical performance evaluations to classify the severity of the condition. Furthermore, EWGSOP-2 recommends use of the SARC-F questionnaire (5) as a tool to identify individuals likely suffering from sarcopenia.

The diagnostic concordance between these two methodologies is recognized as minimal, which has led to disparities in the reported prevalence of sarcopenia, affecting both the general population (6) and individuals with specific conditions (7, 8).

Rheumatoid arthritis (RA), the most commonly diagnosed systemic autoimmune disease, is a complex rheumatic condition characterized by persistent, progressive articular and extra-articular manifestations, ultimately contributing to heightened disability and mortality rates (9, 10).

It is acknowledged that individuals with RA are at an elevated risk for developing sarcopenia compared to the general population (11). Nevertheless, the reported prevalence of sarcopenia among RA patients is highly variable, contingent on the diagnostic definition applied and the demographics of the study population (12).

This study aims to determine the prevalence of sarcopenia within a cohort of elderly Spanish women with RA, examining the application of both EWGSOP-1 and EWGSOP-2 diagnostic criteria. While EWGSOP-2 is the prevailing standard, comparing the two strategies may provide insights into the evolution of diagnostic practices and their potential implications for patient care. Additionally, this research seeks to evaluate the effectiveness of the SARC-F questionnaire in detecting sarcopenia within this demographic.

Our study included a total of 67 patients, as detailed in Table 1. According to the EWGSOP-1 criteria, 43.3% (29/67) of the patients were diagnosed with sarcopenia, and 7.5% (5/67) exhibited severe sarcopenia. Using the EWGSOP-2 criteria, the prevalence of sarcopenia was found to be lower at 16.4% (11/67), with severe sarcopenia observed in 6% (4/67) of the patients. Additionally, 26.9% (18/67) were classified with probable sarcopenia under EWGSOP-2 criteria.

All patients diagnosed with sarcopenia under EWGSOP-2 criteria also met the EWGSOP-1 criteria for sarcopenia. However, the agreement between the two sets of criteria was poor, as indicated by a Cohen's kappa coefficient of 0.409 (p < 0.001), demonstrating significant discrepancies in how each set of criteria categorizes sarcopenia.

The mean SARC-F questionnaire score among the cohort was 2.9 ± 1.9, with 62.7% (42/67) of patients scoring 4 or higher. Patients identified with sarcopenia by EWGSOP-2 criteria had a significantly higher mean SARC-F score of 5.1 ± 1.5, compared to 2.5 ± 1.6 for those without sarcopenia (p < 0.001).

The diagnostic performance of the SARC-F questionnaire is detailed in Table 2, showing its sensitivity, specificity, predictive values, and diagnostic accuracy for diagnosing sarcopenia using EWGSOP-2 criteria.

Recent advancements in RA treatment have markedly improved patient outcomes (17), enabling significant reductions in clinical symptoms, and even disease remission, by targeting inflammatory signals. Alongside the progress being made in managing RA activity, there's a growing recognition of associated comorbidities. Beyond traditional ones, conditions such as sarcopenia are now acknowledged as important considerations in clinical practice (18).

Sarcopenia, a condition marked by muscle loss, significantly impacts elderly patients by increasing the incidence of falls and hospitalization risks, reducing daily living activity capabilities, and elevating morbidity and mortality rates. Its prevalence among older populations notably contributes to frailty and disability, presenting substantial social and economic challenges (19).

Sarcopenia is traditionally classified into one of two categories: primary, attributed solely to aging; and secondary, stemming from other conditions like diseases or treatments. Though considered somewhat outdated, this classification system not only highlights sarcopenia's potential role as a symptom of underlying diseases (1), including cancer, liver, heart, endocrine, or kidney disorders, but also emphasizes its importance as a comorbidity.

RA-induced joint inflammation leads to pain, joint destruction, and reduced physical activity (10). Given that reduced physical activity and chronic inflammation are sarcopenia risk factors, assessing its prevalence in RA patients is pertinent.

Currently, sarcopenia is often undiagnosed, and while universal screening is impractical, a case-finding strategy (1) for opportunistic detection is recommended. This approach is crucial in patients with at higher risk of sarcopenia, such as in older adults or those with chronic diseases, as it will help identify and manage this condition more effectively.

It is well established (20) that the prevalence of sarcopenia in free-living older adults is lower when diagnosed according to EWGSOP-2 criteria vs. EWGSOP-1 criteria. To date, only three studies have compared these criteria in patients with specific diseases. Almeida et al. (7) analyzed both sets of criteria in 57 patients with non-alcoholic fatty liver disease (mean age: 52.7 ± 11.3 years; 75.4% females), finding sarcopenia in 3.5% of cases using only the EWGSOP-1 criteria. Valent et al. (8), studying 81 Parkinson's disease patients (mean age: 73.8 ± 5.3 years; 45% females), reported sarcopenia prevalences of 51.9% with EWGSOP-1 and 28.4% with EWGSOP-2. Lastly, de Freitas et al. (21) examined 242 patients with type 2 diabetes mellitus (mean age: 68.3 ± 5.6 years; 54% females), observing sarcopenia prevalences of 16.9% with EWGSOP-1 and 7% with EWGSOP-2.

We have established that, in the context of RA, the prevalence of sarcopenia significantly diverges depending on whether EWGSOP1 or EWGSOP2 criteria are applied, highlighting a marked discrepancy in agreement between these two diagnostic approaches. The question of whether this variance stems from an overestimation by EWGSOP1 or an underestimation by EWGSOP2 remains to be elucidated through longitudinal studies. Importantly, it must be noted that EWGSOP1 (2) prioritizes muscle mass as the principal diagnostic criterion, whereas EWGSOP2 (3) shifts the focus toward low muscle strength as the primary diagnostic measure. Evidence suggests that muscle strength is a more reliable predictor of adverse health outcomes commonly associated with sarcopenia, including diminished quality of life, increased disability, and higher mortality rates in older populations residing in the community (22). This distinction underscores the need for a nuanced understanding of sarcopenia's diagnostic criteria and their implications for patient outcomes.

Furthermore, gender-specific factors and the severity of RA could have also played critical roles in influencing these prevalence rates. Women with RA often exhibit different clinical outcomes compared to men, which might be reflected in their sarcopenic status when assessed under varying diagnostic criteria. Moreover, the systemic inflammation associated with RA and its treatments can variably affect muscle strength and mass, potentially exacerbating sarcopenia under different diagnostic frameworks.

The data observed in this study has revealed a starker contrast between the two diagnostic tools than what has been reported in prior studies (7, 8, 21). Specifically, the prevalence of sarcopenia identified using EWGSOP-2 criteria was nearly one-third of that detected with EWGSOP-1 criteria. This pronounced difference may be attributed not only to potential disease-specific variations, but also to methodological differences in our approach compared to other studies. Unlike previous research that utilized Bioelectrical Impedance Analysis (BIA) for muscle mass assessment, our study employed Dual-Energy X-ray Absorptiometry (DXA), the gold standard technique for analyzing muscle mass. This methodological distinction likely contributes to the observed discrepancy in sarcopenia prevalence between the two sets of diagnostic criteria.

Information regarding the prevalence of sarcopenia in RA patients, as defined by any of the EWGSOP strategies, remains limited. Specifically, there is a lack of data concerning the frequency of this condition when applying the EWGSOP-1 criteria. Table 3 compiles the primary outcomes from studies published to date (12, 23, 24) that have assessed the prevalence of sarcopenia using the EWGSOP-2 criteria. The prevalence observed has been very close to that reported by Cano-Garcia et al. (24) among a cohort of 77 patients whose clinical and demographic characteristics closely align with those of the current series.

As anticipated, individuals diagnosed with sarcopenia according to both criteria exhibited lower SMI and grip strength. However, it was surprising to note that there were no significant differences in age or gait speed between the groups. Furthermore, while no marked differences were evident in most RA-specific variables, exceptions were noted in terms of disease duration and hemoglobin levels.

Our findings indicate the SARC-F screening questionnaire offers an inherently high sensitivity (100%), a sine qua non condition for diagnosis, as well as good specificity (75%) and diagnostic accuracy (79%) for identifying sarcopenia in RA patients when used alongside the EWGSOP-2 criteria. However, SARC-F is not a good indicator of altered grip strength, SMI or gait speed. Then, in our cohort, the predictive power or SARC-F for decreased muscle strength, mass, and function is notably low. It is conceivable that structural damage associated with RA may introduce a confounding variable, potentially impacting its predictive accuracy.

In healthcare practice, the SARC-F questionnaire seems useful as a screening tool for the presence of sarcopenia in elderly female patients with RA. From an operational perspective, its administration combined with the determination of muscle strength, would help to identify patients with RA who are at risk of developing sarcopenia, eligible to start a multidisciplinary program to prevent it.

The present study has several limitations: (a) its cross-sectional design precludes establishing causality between RA characteristics or evolution and the presence of sarcopenia; (b) it exclusively involved elderly women, since it focused on the group most at risk for sarcopenia; and (c) it was localized to a single center, though it is believed to reflect typical characteristics of established RA patients.

Moreover, the sample size was determined using the best available prevalence at the time the study was planned, which was 4.5% for sarcopenia in individuals with RA (12). However, the study found an observed prevalence of 16.4%, significantly exceeding expectations. This significant discrepancy suggests that the sample size may have been too small to achieve optimal statistical power and precision, considering the actual variability within the study population.

Considering all these limitations, caution must be exercised in generalizing findings. Indeed, broader, longitudinal studies are needed to confirm these observations and extend them to a more diverse population. Future studies should also consider recalculating the necessary sample size using this newly observed prevalence to enhance the robustness of the findings.

Nevertheless, it makes significant contributions to the field by comparing EWGSOP-1 and EWGSOP-2 criteria for screening sarcopenia in an elderly female RA cohort, thus constituting a novel approach in this area. Additionally, it evaluates the SARC-F questionnaire's effectiveness in detecting sarcopenia among RA patients, an aspect not previously explored.

This study, conducted among elderly Spanish women with RA, highlights that the detected prevalence rates of sarcopenia significantly differ based on the application of EWGSOP1 or EWGSOP2 criteria. Moreover, the SARC-F questionnaire shows good effectivity for predicting sarcopenia following the EWGSOP2 criteria, currently the most widely accepted in clinical practice. This underscores the importance of selecting appropriate diagnostic strategies for sarcopenia in RA patients, which can impact both clinical outcomes and management strategies.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the IDIBELL Clinical Research Ethics Committee of Bellvitge. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

LV-M: Data curation, Formal analysis, Investigation, Methodology, Validation, Writing – original draft, Writing – review & editing. CG-V: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Writing – original draft, Writing – review & editing. MM: Data curation, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. LB-A: Data curation, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. DB: Data curation, Formal analysis, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. JN: Data curation, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. XJ: Data curation, Investigation, Methodology, Software, Writing – original draft, Writing – review & editing. JMN: Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Supervision, Validation, Writing – original draft, Writing – review & editing.