Background/Purpose:

Muscle MRI is used to describe the myositis component of the anti-synthetase syndrome (ASS), but the value of the examination is limited by lack of reference data from non-myositis populations. The primary aim of this study was therefore to compare the MRI findings in ASS with healthy age- and gender matched controls.

Methods:

In September 2011, 68/70 ASS patients in the Oslo University Hospital ASS cohort were included in a comparative, cross-sectional study that included muscle MRI, manual muscle testing of 24 muscles (MMT24) and plasma CK. Sex and age-matched healthy controls were randomly collected from the National People Register of Norway in a 1:1 proportion (N=67).  MRI was using a 1.5 T scanner with coronal and axial T1-weighted spin echo and short T1 inversion recovery (STIR) sequences of thigh muscles. The images were analyzed by two radiologists blinded for the participant’s status. Edema in muscles or fascia was evaluated as present/not present. Fatty infiltration was scored according to the Guttalier grading (0-4) and considered pathological if > 2 [1]. Elevated CK was defined as > 2x upper limit of normal (ULN). The MMT24 score (0-140) was performed by two experienced physiotherapists. Chi-Square and Mann Whitney U-test were used to evaluate statistical significance (p<0.05). Pearson’s correlation was used to detect correlations.

Results:

Median disease duration for the ASS patients was 71 months and 76% had previously been diagnosed with myositis. Abnormal MRI findings were found in 63% of the patients compared to 18 % in the controls with significant differences in the proportion of muscle and fascia edema, as well as fatty infiltration (Table 1). The MRI findings in the control group were to some extent asymmetric. Median MMT24 scores were lower in ASS than controls, but CK levels did not differ between the groups (Table 1). In ASS patients no correlation was seen between muscle-edema and elevated CK or between MMT24 and elevated CK. MRI abnormalities were detected in 35/52 ASS patients with myositis and in 7/15 cases with no previous myositis signs. There was no difference in MMT24 or CK values between the two ASS subsets. Of the 12 controls with abnormal MRI findings, only one had elevated CK and three had MMT24 score ≤ 137.

Table 1; MRI findings, MMT24 and CK levels in ASS patients and matched controls

Conclusion:

This comparative study reports significant differences in myositis-related MRI findings between ASS patients and matched controls. Muscle-edema was present in 37% of ASS patients with normal CK but only in 10% of the controls. The study shows that MRI has potential as a complementary tool to assess myositis in ASS, and highlights the need for MRI scoring systems that differentiate patients from controls.

References;

1. Goutallier, D., et al., Influence of cuff muscle fatty degeneration on anatomic and functional outcomes after simple suture of full-thickness tears. J Shoulder Elbow Surg, 2003. 12(6): p. 550-4.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/correlations-between-muscle-mri-muscle-strength-and-creatine-kinase-levels-in-the-anti-synthetase-syndrome-a-comparative-cross-sectional-study/