Characteristic manifestation of muscle pathology and the lower extremity magnetic resonance imaging and classification in patients with single-organ skeletal muscle vasculitis
Objective:To describe the characteristic muscle pathology and lower extremity magnetic resonance imaging(MRI)findings of lower extremity muscles in patients with histopathological proven single-organ skele-tal muscle vasculitis(SoSMV).Methods:The lower extremity MRI scans and muscle histological slides of pa-tients with SoSMV diagnosis over 6 years were retrospectively evaluated.T1-weighted(T1WI)and T2-weighted fat-suppressed images(T2WI-fs)were available for all patients;additionally,in some cases gadolinium-en-hanced T1-weighted fat-suppressed images(Gd-T1WI-fs)were also obtained.Results:A number of 13 patients were examined(7 males;median age[interquartile range]49 years[25-70]).Two distinct types of SoSMV were observed on MRI and pathology.For type-1 SoSMV(n=6),necrotizing vasculitis was detected in 4 pa-tients and vessels with occluded lumen were identified in 5.Myofiber degeneration and necrosis,accompanied with inflammation and fibrosis were features in 5 and extensive in 3 of them.The affected muscles demon-strated hypointensively swelling with loss of the interspersed intramuscular fat on T1WI,diffuse hyperintense signal on T2WI-fs,and homogeneous enhancement on Gd-T1W-fs images(n=2).For type-2 SoSMV(n=7),peri-vasculitis and non-necrotizing vasculitis without occluded lumen were documented in all.The involved mus-cles revealed poorly defined,striated,and ramified hyperintense signals on axial T2WI-fs images,with the presence of a distinctive presentation,named as"fishbone sign".The same areas were normal appearance on T1WI images and were slightly enhanced on Gd-T1WI-fs images(n=3).Conclusion:Lower extremity MRI scans showed a pattern of characteristic findings that was distinctive from different disease types,and might be useful non-invasively for assisting with the diagnosis,classification and outcome prediction of SoSMV.
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