Discussion
The present study provides data on the US PD findings of a population of patients with SLE without musculoskleletal signs or symptoms, in comparison with symptomatic patients with SLE and healthy controls. In our study, US revealed SH of the hand or wrist in 8% of the examined joints and in 77% of patients with SLE who denied arthralgia and did not present abnormalities on physical examination. The majority of these patients presented minimal SH (score 1) without associated PD, which could be considered normal, according to previous literature.13 ,30 ,33 However, abnormal US findings (SH≥2 or PD signal) were seen in 23% of patients. We believe that these findings indicate subclinical joint inflammation. Accordingly, while minimal SH was detected in 50% of the controls, none presented abnormal SH (score≥2) or positive PD signal.
While a number of studies have recently described US findings in the SLE population, only some of these included patients who did not complain of musculoskeletal symptoms at the time of the US evaluation,5 ,35–39 and, to our knowledge, only one focused on asymptomatic patients.14 In these studies, the prevalence of US abnormalities in asymptomatic patients with SLE varied from 3% to 58%.5 ,13 ,36–38 This inconsistency is thought to be related to US reporting methodologies, mostly due to the lack of consensus about the definition of a positive US examination. Most studies defined synovitis as SH grade 1 or higher; however, grade 1 synovitis without PD can be found in healthy subjects and in patients with osteoarthritis.13 ,33 In addition, while the majority of studies described a semi-quantitative grading score in the methodology, results were most often presented as binary (synovitis/no synovitis), and the prevalence of each SH score was usually not addressed.13 Furthermore, to our knowledge, only a limited number of studies described global US scores in patients with SLE.14 ,39
Our study contributes to a better understanding of subclinical joint disease in patients with SLE, as it provides a detailed description of the US PD findings both at joint level and at population level and characterises the groups of patients and controls by using two sets of global US scores. SH index and GLOESS scores were similar in the asymptomatic SLE group; however, in the symptomatic group GLOESS values were slightly higher. We believe GLOESS may be advantageous, as it includes information about SH and PD signal in the same score. Although the prevalence of asymptomatic patients with SLE with SH did not reach statistical significance in comparison to healthy controls, both SH index and GLOESS were significantly higher in the asymptomatic SLE population when compared with the control group. Altogether, these findings encourage the use of global US scores for a more detailed joint evaluation in SLE, in clinical practice and in future trials.
Compared with the study of Yoon et al,14 our study detected a higher prevalence of SH (grade≥1) in asymptomatic patients with SLE. While the previous study identified joint effusion and/or SH in 58% of asymptomatic patients with SLE, we detected SH (grade ≥1) in 77% asymptomatic patients with SLE. This may be due to the larger number of joints examined in our study (22 joints per patient, in comparison with 3 joint recesses in the previous study—wrist, 2nd and 3rd MCP) and to the higher frequency of our linear array probe (15 MHz, in comparison to 10 MHz in the previous study). However, while the previous study classified these 58% of patients as having subclinical synovitis, only 23% of the asymptomatic patients with SLE in our study were classified as having subclinical joint inflammation.
In our study, patients with abnormal US PD findings did not show significant differences regarding demographic, clinical and laboratory data when compared with those with normal US PD findings. In addition, no significant correlation was found between US PD variables and disease activity or organ damage scores. This is in agreement with several previous studies, suggesting that global assessment of patients with SLE should be complemented by imaging modalities, such as US.35 ,37 ,39 Interestingly, patients under treatment with oral prednisolone had higher PD indexes. In addition, the prevalence of PD signal and PD indexes were significantly higher in the symptomatic patients with SLE when compared with the asymptomatic patients and controls, suggesting that PD signal could be considered a marker for active musculoskeletal disease.36
The most important limitations of our study are the moderate sample size (which may limit generalisability) and the high prevalence of steroid use among the SLE population (which could reduce the global inflammatory burden and result in lower prevalence and grading of the US PD findings). Furthermore, intake of non-steroidal anti-inflammatory drugs at the time of US imaging, a potential confounder in US PD evaluation, was not accounted for. Although US-detected subclinical joint abnormalities have been previously associated with the development of musculoskeletal symptoms, the prognostic value of these findings remains to be determined. Larger longitudinal studies are required to confirm the significance of subclinical US PD findings, specifically regarding the predictive value for the development of long-term joint damage.13 ,40
In conclusion, a small subgroup of patients with SLE without artralgia or clinical evidence of arthritis may present subclinical joint inflammation. Global US scores and PD signal may be important in disease evaluation and therapeutical monitoring.