AB1501 MUSCLE BIOPSY PRACTICES: AN INTERNATIONAL SURVEY (2023)

<h3>Background</h3> Muscle biopsy is an important tool in assessment of idiopathic inflammatory myopathies (IIM), however the optimal approach is unknown. A variety of biopsy procedural techniques have been reported including open surgical biopsy, percutaneous needle biopsy and Conchotome forceps biopsy. <h3>Objectives</h3> This study aimed to describe current practices in obtaining a muscle biopsy amongst international experts who manage people with IIM. <h3>Methods</h3> An e-survey was designed and piloted to collect information regarding muscle biopsy practices. The e-survey was disseminated to members of the International Myositis Assessment and Clinical Studies (IMACS) group. Snowball sampling was used, whereby IMACS members were invited to forward the survey link to other clinicians involved in care of people with IIM. Information regarding respondent characteristics and their current practice in obtaining muscle tissue was collected. The e-survey was available for completion between 20<sup>th</sup> October 2022 and 20<sup>th</sup> of January 2023. Participants were included if they self-reported being a clinician or researcher with experience in IIM. Results were analysed using descriptive statistics. <h3>Results</h3> One hundred and one respondents completed the survey by 12<sup>th</sup> January 2023. Most respondents were from Europe (22.7%) and the United States (22.7%) followed by Asia (7.9%). The majority of respondents were rheumatologists (74.3%) and neurologists (20.8%) working in academic settings (73.3%). Open surgical biopsy was the most common method of muscle sampling (Table 1). Open surgical biopsies were often performed under local anaesthesia (55.6%) and without sedation (50.0%) or general anaesthesia (58.9%). Clinical examination was frequently used to guide muscle selection (85.4%), followed by MRI (50.0%) and EMG (43.8%). The influence of clinical and laboratory characteristics on decision to pursue muscle biopsy are presented in Figure 1. Many respondents were more likely to pursue diagnostic biopsy in the setting of seronegativity (65.6%), abnormal MRI (58.3%) and abnormal neurophysiology (56.3%). Conversely, many were less likely to pursue diagnostic biopsy in setting of positive myositis specific antibodies (53.2%) or classic dermatomyositis rash (70.8%). Low complication rates were reported for all muscle biopsy techniques. Non-diagnostic histopathology was reported as ‘common’ (observed rate between 1-10%) in 30.5% and ‘very common’ (observed rate ≥10%) in 14.8% of respondents. <h3>Conclusion</h3> Open surgical biopsy was the most common muscle biopsy approach reported by international experts who manage IIM. Clinical examination, MRI and EMG were frequently used to select a muscle to biopsy. Serology, radiographic and neurophysiological status and the presence of a classic dermatomyositis rash influence the decision to pursue diagnostic biopsy. Muscle biopsy is safe, although non-diagnostic histopathology was commonly reported regardless of technique. <h3>Reference</h3> Nil. <h3>Acknowledgements</h3> The authors would like to acknowledge the International Myositis Assessment and Clinical Studies group for their feedback regarding the survey and permission to disseminate the survey to their members. <h3>Disclosure of Interests</h3> None Declared.