Introduction

Idiopathic inflammatory myopathy (IIM) is a group of systematic autoimmune disorders with a global average prevalence of 4.27-7.89/ 100,000 individuals1. Polymyositis (PM) and dermatomyositis (DM) are the most common types of IIM, affecting skeletal muscles and internal organs2. Myocardial involvement happens frequently in PM and DM but is subclinical in most cases2-4. Cardiac magnetic resonance (CMR) imaging is emerging as a non-invasive and reliable tool for facilitating the diagnosis of myocarditis4, 5 and myocardial involvement in autoimmune diseases6. This study was aimed to investigate myocardial involvement characteristics and compare its differences in patients with PM and DM by CMR.

Methods

A total of 17 PM and 27 DM were enrolled in this retrospectively study. A 3T MR scanner (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany) was used for all the CMR scan. CMR 2-chamber, 4-chamber, and shot-axis cine images were derived with a standard segmented balanced steady-state free-processing (bSSFP) sequence. The typical parameters were as follows: field of view (FOV), 340-380 mm; repetition time (TR)/echo time (TE), 3.4/1.4 ms; matrix size, 208×188; voxel size, 1.6×1.6×8.0 mm3; bandwidth, 962 Hz/px; flip angle (FA), 47°; slice thickness, 8 mm; and inter-slice gap, 2 mm. LGE images were acquired 8–15 min after intravenous administration of gadolinium-DTPA (Magnevist, Bayer, Berlin, Germany) at a dose of 0.2 mmol/kg in short-axis stack using a phase-sensitive inversion-recovery (PSIR) gradient echo sequence. Inversion times were adjusted to null the signal from normal myocardium (FOV, 340-380 mm2; matrix size, 256×220; voxel size, 1.3×1.3×8.0 mm3; bandwidth, 781 Hz/px; TR, 485 ms; TE, 1.24 ms; FA, 55°). Typical parameters of motion-corrected basal, mid, and apical level of LV short-axis Modified Look-Locker inversion-recovery (MOLLI) T1-mapping sequence with a 5b(3b)3b scheme before and 15-20 min after intravenous contrast agent injection were as follows: FOV, 340-380 mm; matrix size, 192×172; voxel size, 1.3×1.3×8.0 mm3; bandwidth, 1085 Hz/px; TR/TE, 2.9/1.15 ms; and FA, 35°. Inversion time was individually adjusted for complete nulling of the myocardium. T2 mapping was acquired with the same image planes as T1 mapping using a T2-prepared sequence with three different TE times (0 ms, 30 ms, 55 ms). Left ventricular (LV) morphologic and functional parameters and CMR tissue characterization imaging, including global native T1, T2, extracellular volume (ECV), and late gadolinium enhancement (LGE), were analyzed using the cvi42 software (Circle Cardiovascular Imaging Inc., Calgary, Alberta, Canada). Global native T1, T2, and ECV were analyzed by the 16 American Heart Association (AHA) segment.

Results

The LGE, T1, and ECV maps of one PM and one DM patient are shown in Figure 1. Patients in the PM/DM group showed elevated global native T1 and ECV values (Table 1). Global ECV values were higher in the PM group when compared to the DM group (ECV, 33 ± 3 % vs. 30 ± 4 %; p = 0.039) (Figure 2). PM and DM groups showed a different positive segment distribution of native T1, T2, and ECV, where positive segments of in PM patients were more than those of DM patients (Figure 3). No significant differences in LV functional parameters were observed between PM and DM groups, and most of them were in normal range (Table 1).

Discussion

In this study, we retrospectively evaluated the CMR parameters of PM and DM patients. Although the laboratory characteristics were elevated, the PM/DM group showed a normal LV volume and EF values, thereby suggesting the subclinical stage. Our data revealed two patterns of myocardial damage. For PM patients, LGE with patchy or strip was specifically tendency located at interventricular septum and insertion sites, especially insertion sites. For DM patients, LGE tendency occurs in the interventricular septum and inferior segments with non-ischemic pattern. In our cohort, the mean global ECV was higher in PM patients compared with DM patients, which proved that PM patients had a tendency of higher myocardial involvement when compared to DM patients. In our analysis, we differentiated myocardium segments, instead of analyzing as a whole as seen in most published studies7. Segmental analysis of global native T1 values in patients with PM and DM showed that the prolonged native T1 values predominately involved segments of the interventricular septum, but the number of prolonged native T1 segments of PM were more than those of DM. Moreover, the number of prolonged ECV segments were more than the prolonged native T1 segments in both PM and DM patients, but the number of prolonged ECV segments of PM were also more than that of DM. The prolonged native T1 and ECV values reflect necrosis and fibrosis, which can lead to both conduction disturbances and supraventricular or ventricular arrhythmias as demonstrated in previous studies8. Our results suggested that PM patients had a tendency of a wider range of myocardial necrosis and fibrosis than DM patients.

Conclusions

In conclusion, CMR tissue characterization imaging provided excellent performance for assessing the myocardial involvement in PM and DM patients with normal left ventricular function during the subclinical stage. Furthermore, the characteristics of myocardial involvement was different between PM patients and DM patients, and myocardial involvement in patients with PM was more serious when compared to patients with DM.

Acknowledgements

No acknowledgement found.

References

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