Diagnostic testing in patients suspected of treatable idiopathic inflammatory myopathy: a prospective multimodality diagnostic accuracy study

Diagnosing idiopathic inflammatory myopathy (IIM) is challenging due to the absence of a gold standard and the uncertainty among physicians regarding the optimal diagnostic approach. Available diagnostic tests are autoantibody testing, MRI, electromyography (EMG), ultrasound (US) and muscle biopsy. The diagnostic performance of individual tests and combined strategies is unclear.

This prospective diagnostic study evaluated diagnostic accuracy and patient-reported burden across multiple modalities and strategies in patients with suspected IIM. Individual tests showed limited sensitivity or specificity, but strategies combining autoantibody testing with MRI, EMG or ultrasound and selective muscle biopsy achieved the best diagnostic accuracy with moderate burden. Several strategies with high diagnostic performance were identified, enabling clinicians to choose based on local availability and feasibility.

This study identifies high-performing diagnostic strategies for suspected IIM that may support clinical decision-making...