Patients
We retrospectively analysed the shoulder ultrasonographic findings in patients with PMR and FS who visited a tertiary hospital in China from July 2020 to April 2022. These patients were diagnosed with PMR or FS by rheumatologists, orthopaedic surgeons, or rehabilitation physicians and met the inclusion criteria. In terms of PMR, patients were included if they ① met the PMR classification criteria of 2012 EULAR/ACR[5], had a disease duration of less than 6 months; and ② used nonsteroidal anti-inflammatory drugs (NSAIDs) or disease-modifying anti-rheumatic drugs for less than one week. In terms of FS, patients were included if they ① had shoulder pain with limited passive movement, specifically less than 30 degrees in two or more planes[7], were diagnosed as having stage II FS as defined by Hannafin and Chiaia [8], had a disease duration of less than 6 months, and used NSAIDs. Patients were excluded if they took glucocorticoids within a week prior to the ultrasound; received a peripheral shoulder injection, sustained shoulder trauma, or underwent shoulder surgery within 3 months prior to the ultrasound; had a shoulder joint infectious disease, rheumatoid arthritis, giant cell arteritis or other rheumatic diseases; or had incomplete medical history information, including only unilateral shoulder ultrasound findings.
According to the inclusion and exclusion criteria, the eligible samples from 169 PMR patients were finally screened and matched 1:1 to 367 FS patients according to the age ± 3 years. Finally, 23 groups of patients with PMR and FS were included in a matched-pair analysis. The clinical diagnosis of PMR was confirmed independently by two rheumatologists (TY and QY), and the diagnosis of FS was confirmed independently by two orthopaedic surgeons (DS and HX). If there was ambiguity with respect to the diagnosis, it was excluded.
Due to the retrospective nature of the study, the requirement for written informed consent was waived but verbal informed consent was obtained by telephone from all the patients. Ethics approval was obtained from the institutional ethics board (JXEY-2022ZFYJ213).
2.2 Ultrasound Protocol and definition
All the ultrasound images of the bilateral shoulder joints of the PMR and FS patients were assessed by members of the facility's musculoskeletal ultrasound team, who all had more than 10 years of experience in diagnostic ultrasound. Subsequently, the data from the medical record system were rereviewed from May-July 2022 by two sonographers (CL, WS) who were blinded to the clinical and laboratory findings.
All eligible patients had undergone ultrasound examinations of both shoulders, and the results of the severe side were selected for statistical analysis. The IPQ-7 ultrasound diagnostic device (Philips, the Netherlands) was used with a line array probe (frequency ranging from 5 to 12 MHz). The ultrasound review focused on subacromial-subdeltoid (SASD) bursitis, long head of biceps (LHB) tenosynovitis, inferior GH synovitis, and the presence of a rotator cuff lesion[9]. LHB tenosynovitis was considered if the maximal thickness of the hypoechoic fluid around the biceps tendon was > 2 mm[9]. SASD bursitis was diagnosed if the maximal thickness of the hypoechoic fluid-filled bursa was > 2 mm[9]. The axillary pouch thickness was measured as the distance from the bony cortex of the humerus to the outer margin of the capsule. If the axillary pouch thickness was > 3.5 mm (inferior GH synovitis) [9, 10], GH synovitis was considered.
3.3 Statistical analysis
Dichotomous variables are expressed as absolute frequencies (percentages) and were compared using Fisher's exact test. Continuous variables are described using medians [interquartile ranges (IQRs)], and statistical comparison between the groups was performed with the Mann‒Whitney nonparametric U test. P values less than 0.05 were considered indicative of statistical significance. All statistical calculations were performed using SPSS statistical software (IBM SPSS version 19), and GraphPad Prism version 8 software was used to plot graphs and receiver operating characteristic (ROC) curves.