Whole-body muscle magnetic resonance imaging in patients with muscle symptoms: incidental findings and outcomes

Background and purpose Whole-body muscle magnetic resonance imaging (MRI) has become widely used for diagnostic workup in patients with muscle diseases. The prevalence of incidental findings in diagnostic whole-body muscle MRI is unknown. Here, the prevalence and outcomes of incidentalomas in whole-body muscle MRI in a large cohort of patients with muscle symptoms were studied. Methods Two hundred and six patients who consulted at our neuromuscular clinic with muscle weakness and/or myalgia and/or increased serum creatine kinase and in whom a whole-body muscle MRI was performed between January 2016 and March 2020 were included. Results Whole-body muscle MRI revealed at least one incidentaloma in 132 patients (64.1%), with mean age at MRI examination 50.4 years (19-74 years). Most of the incidental findings were benign. However, diagnostic examinations were indicated in 16.3% of the incidentalomas, treatment was needed in 4.7% and, in retrospect, symptoms related to the incidental findings were identified in 14.3%. Three malignant (glioblastoma multiforme, renal cell carcinoma and hepato-splenomegaly related to a lymphoma) and one precancerous (low-grade appendiceal mucinous neoplasm) incidental findings were identified. In one patient an abdominal aortic aneurysm was detected and in another a large cerebral arteriovenous malformation. In 1.2% of the incidentalomas, i.e. periventricular white matter lesions (LAMA2mutations) and fibrous dysplasia (ANO5mutations), an indirect link with the muscle disease could be established. Conclusions It is concluded that incidental findings in diagnostic whole-body muscle MRI in patients with muscle symptoms occur frequently. Most of them are benign, but in some timely detecting the incidentaloma leads to early treatment and can thus impact prognosis.