SpA is a chronic inflammatory disease that includes several subtypes, and sarcopenia is a progressive and complex disease that may be associated with it. Sarcopenia has been found to be strongly associated with a range of adverse outcomes, including increased disability, reduced quality of life, and higher mortality rates, even amone young individuals [30]. Therefore, exploring the prevalence of sarcopenia in SpA patients has important clinical implications, and then identifying and managing it is crucial for improving overall health outcomes. The purpose of this study is to gather and analyze all existing research on the prevalence of sarcopenia in SpA patients in order to provide a more accurate estimate of the condition’s occurrence within this specific disease. To our knowledge, this is the first systematic review and meta-analysis that investigates the overall prevalence of sarcopenia, presarcopenia and severe sarcopenia in SpA patients. Due to the significant clinical, methodological, and statistical heterogeneity observed among the included studies, we did not conduct the publication bias and sensitivity analysis. It is worth mentioning that certain studies reported a prevalence of zero for sarcopenia [22, 27], therefore we utilized the ‘metaprop’ to address this issue. Furthermore, it is important to note that some subgroups had a limited number of studies (1 or 2), which precluded the heterogeneity test.

Our study included 16 studies and 999 SpA patients that met the inclusion criteria. The overall prevalence ranged from 0 to 80.0% in sarcopenia, 5.4 to 49.3% in presarcopenia and 4.9 to 15.7% in severe sarcopenia. The findings suggest that sarcopenia is more prevalent in SpA compared to control groups in most of the studies. Compared to the prevalence of general sarcopenia without any other diseases (10–27%) [31], risk of muscular atrophy in SpA is increased to some extent. Furthermore, our meta-analysis revealed a notable trend and suggested that individuals with sarcopenia in SpA tend to be of advanced age (42.3 vs. 40.9 [21], 32.6 vs. 36.6 [28]), have a longer duration of the disease (11.6 vs. 9.3 [21], 12.4 vs. 6.9 [28]) and a lower BMI (21.6 vs. 25.3 [21], 24 vs. 28.8 [17], 20.1 vs. 28.4 [28]). Even in the case of presarcopenia, we can still observe this trend in the demographics [21]. Especially, in the study conducted by Neto et al., none of the participants were found to have sarcopenia. However, these patients still experienced reduced physical performance and lower strength than the healthy controls, despite having normal muscle mass. This suggesting the presence of possible muscle dysfunction [22]. Besides, in the cohort study, SpA patients underwent medical intervention, resulting in a decrease in disease activity. Additionally, an increase in muscle mass was observed [16, 23]. However, it remains unclear whether the improvement should be attributed to the direct effect of the medication or the indirect effect following improvement in symptoms. According to a study on global prevalence of sarcopenia, the average age was 68.5 years old [31]. In contrast, our study found that the average age of sarcopenia in SpA patients was significantly younger. All of these findings hightlight the importance for clinicians to carefully consider these risk factors when assessing and managing sarcopenia in SpA.

As we known, sarcopenia is influenced by various factors, such as age, sex, level of inflammation, disease duration, BMI, and treatment [3]. In this study, we collected patient characteristics including age, sex, disease duration, BMI, and sample size. In addition to assessing muscle mass, muscle strength, and physical performance, we also gathered information on sarcopeniat classification, measurement methods, and correction methods, as presented in Table 2. However, it is unfortunate that this part of the content is quite incomplete. Consequently, we were unable to further adjust for risk factors such as age and sex. And we strongly encourage follow-up studies to provide detailed explanations of these relevant factors.

The prevalence of sarcopenia varied between regions. Most of studies were conducted in Europe, with the highest prevalence rate of sarcopenia observed in Portugal/Europe (48/60) [14], while the lowest rate was also reported in Portugal/Europe (0/27) [22]. This may be related to limited studies conducted in other regions, like Asia and Africa. In measuring muscle mass, DXA was found to be the most commonly used method, followed by BIA. Although these methods are golden rules for sarcopenia, considering the presence of limited medical conditions in reality, more and more researchers have begun exploring the role of computed tomography, magnetic resonance imaging and ultrasonography in measuring muscle mass. In our systematic review, the study conducted by Soto et al. identified the potential of ultrasound in diagnosing sarcopenia in SpA [26]. The AWGS had even suggested the concept of “potential sarcopenia” which can be identified through simple methods such as finger-ring test [11]. Subsequently, this can guide healthcare practitioners to conduct more specialized examinations, making it applicable for primary healthcare facilities and aiding in early intervention. In conclusion, diagnostic tools may have a significant impact on the detection rate of sarcopenia.

Our study included 5 major classifications of sarcopenia with different cut-off points and instruments to assess muscle mass, the most commonly reported classification of them was the EWGSOP, followed by the EWGSOP2, AWGS, Baumgartner and Lee’s equation. Meanwhile, we estimated that the overall prevalence of sarcopenia was 21.3% in EWGSOP, 3.8% in EWGSOP2, 24.7% in AWGS, 21.7% in Baumgartner and 70.8% in Lee’s equation. The first three diagnostic criteria are widely recognized. However, the diagnostic criteria proposed by Baumgartner in 1998, which defines sarcopenia as a relative SMI less than 2 standard deviations from healthy individuals of the same sex, has its limitations. This method, which evaluates only muscle mass, lacks a comparative measure of muscle strength that is included in other contemporary diagnostic criteria for sarcopenia. Despite this, due to its simplicity and ease of use, it remains a popular choice for epidemiological investigations into sarcopenia. Lee et al. developed a predictive model that primarily incorporates measurements of limb circumference and skinfold thickness, with adjustments made for variables such as sex, age, and ethnicity [13]. This model has been validated in both non-obese and obese populations. However, its application remains limited due to the scarcity of related studies. In contrast, the diagnostic criteria proposed by the EWGSOP and AWGS are more comprehensive. They consider three key factors: loss of muscle mass, decreased muscle strength and reduced physical performance, each with their respective cut-off values, as shown in Table 1. This multifaceted approach provides a more holistic evaluation of sarcopenia. These variations in diagnostic criteria may also contribute to the disparities in the prevalence of sarcopenia.

In this study, the lack of primary data from various studies prevented the establishment of a uniform classification, which may account for the differences in prevalence observed between different studies. For instance, Song et al. conducted a study in South Korea involving 60 patients with AS, utilizing both the AWGS and Korea criteria. They found that the prevalence of sarcopenia was 15% and 16.7%, respectively, resulting in a subtle difference [25]. Furthermore, as mentioned earlier, the previous classification such as Baumgartner and Lee’s equation have their limitations, and there may be a certain disparity between the classification widely accepted in recent years. Unfortunately, standardization these studies in assessing the prevalence of sarcopenia in SpA is currently not possible. However, this emphasizes the importance of recognizing the impact of ongoing improvements in classification on sarcopenia prevalence in real-world settings.

It is well known that SpA has various subtypes, but there has been no research comparing the prevalence of sarcopenia among different subtypes. After conducting an initial search, we found three studies related to sarcopenia in JIA [32,33,34]. Unfortunately, these articles did not provide specific and clear information regarding the subtypes of JIA included. Only one article mentioned the inclusion of various subtypes of JIA. As a result, we decided not to include these articles in our study. However, the JIA group showed a surprisingly high prevalence of sarcopenia, reaching 71.4%. In contrast, the prevalence of sarcopenia in the subtypes of AS or PSA was relatively lower and have no significant differences (20.1% vs. 19.8%), which may be attributed to the larger number of patients included. Furthermore, several studies had shown a correlation between the risk of sarcopenia and disease activity. However, additional research is required to validate these findings using a larger sample size and to explore the factors that influence the development of sarcopenia in SpA patients. Future research that investigates the differences in sarcopenia status among these subtypes could provide valuable insights into the shared pathophysiology between sarcopenia and SpA.

In previous studies, men are more commonly affected in SpA patients, while women are more commonly affected by sarcopenia [35]. However, many studies did not provide specific information regarding sex classification. In our study, 6 articles specifically described the prevalence of sarcopenia in men, while five articles specifically focused on the prevalence of sarcopenia in women. In fact, some studies only included male participants, while others only included female participants. Overall, sex differences in the prevalence of sarcopenia among SpA patients had not been observed (men: 20.7% vs. women: 20%) and several factors may contribute to it, like hormonal differences, physical activity, nutritional status and biological factors, all of them could influence the development of sarcopenia [35, 36]. Further research is needed to better understand the role that sex plays in the development of sarcopenia and to establish appropriate interventions to improve it in both men and women patients in SpA.

By conducting a systematic review and meta-analysis, we obtained a more robust and reliable understanding of the prevalence of sarcopenia in SpA by pooling data from multiple studies. Our findings demonstrate that sarcopenia is prevalent in SpA, generally higher than estimates previously reported from the general population. The detrimental effects of sarcopenia, such as an increased risk of falling and fractures, impairment of independence and quality of life, and the likelihood of mobility disorders, have been well documented. This highlights the importance of early clinical assessment and interventions to prevent adverse outcomes associated with muscle atrophy in SpA patients. Addressing the components of presarcopenia at an early stage could have benefits in preventing and reversing sarcopenia. In terms of treatment, resistance training and nutritious supplementary have been widely agreed in managing sarcopenia [37, 38], while further research is needed to establish their specific benefits in SpA.

It is important to acknowledge the limitations of our study. Firstly, the studies included in our analysis had varying definitions and cut-offs for sarcopenia, leading to heterogeneity in our findings. Additionally, the criteria used for diagnosing sarcopenia may not be appropriate for the specific disease, future research should aim to establish standardized definitions and criteria for diagnosing sarcopenia in SpA. Secondly, the majority of the studies included in our analysis were cross section surveys, which limited our ability to investigate the cause and effect relationship between SpA and sarcopenia. Longitudinal studies are needed to better understand the relationship between sarcopenia and the progression of SpA over time. Thirdly, it is important to consider that different types of SpA may exhibit distinct characteristics. Factors such as age, sex, level of inflammation, disease duration, BMI, and treatment may influence the prevalence and severity of sarcopenia. Future studies should take these factors into account to investigate their impact on sarcopenia in SpA.