Impact of muscle biopsy on the clinical decision-making process in patients with suspected idiopathic inflammatory myopathy.

BACKGROUND: The significance of muscle biopsy as a diagnostic tool in idiopathic inflammatory myopathies (IIM) remains elusive. We aimed to determine the diagnostic weight that has been given to muscle biopsy in patients with suspected IIM, particularly in terms of clinical diagnosis and therapeutic decisions. MATERIAL AND METHODS: In this retrospective multicentric study, we analyzed muscle biopsy results of adult patients with suspected IIM referred to a tertiary center between January 1, 2007, and October 31, 2021. Information regarding referral department, suspected diagnosis, biopsy site, demographic, clinical, laboratory data, and imaging results were extracted. Statistical analyses included the level of agreement between suspected and histological diagnosis and calculation of diagnostic performance (positive and negative predictive values, positive and negative likelihood ratios, sensitivity, and specificity of muscle biopsy in relation to clinical diagnosis and/or treatment initiation). Performance was tested in different strata based on clinical pre-test probability. RESULTS: Among 758 muscle biopsies, IIM was histologically compatible in 357/758 (47.1%) cases. Proportion of IIM was higher if there was a solid clinical pre-test probability (64.3% vs. 42.4% vs. 48% for high, medium and low pre-test probability). Sensitivity and specificity of muscle biopsy were highest (82%) when the diagnosis by the clinician was used as outcome scenario. Negative predictive value was only moderate (between 63% and 80%) and lowest if autoantibodies were positive (35%). CONCLUSION: In patients with clinically suspected IIM, approximately 50% of biopsies revealed features indicative of IIM. Diagnostic performance of muscle biopsy was moderate to high depending on clinical pre-test probability.

Serum Interleukin-37: a new player in Lupus Nephritis?

INTRODUCTION: Interleukin-37 (IL-37) has been proved to be a fundamental natural suppressor of innate immunity and inflammatory responses in autoimmune diseases such as systemic lupus erythematous (SLE). The purpose of this study was to assess serum IL-37 level in SLE patients and its correlation with disease activity and clinical and laboratory manifestations of SLE patients. PATIENTS/METHODS: The serum level of IL-37 was assessed and analyzed in 100 SLE patients and 50 healthy controls by using enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory manifestations and disease activity using SLE Disease Activity Index (SLEDAI) were also assessed. RESULTS: IL-37 serum level was significantly higher among SLE patients than controls. It has statistically significant correlation with disease activity, renal and mucocutaneous involvement in SLE patients. CONCLUSION: IL-37 level is elevated in SLE patients in comparison to healthy controls and is correlated to high disease activity, mucocutaneous and renal involvement.