Background Muscle inflammation and damage is observed in many diseases and may be associated with various etiologies. Muscle enzymes, acute phase reactants, electromyography, muscle biopsies, and a variety of imaging techniques have been utilized to investigate this inflammation.

Muscle magnetic resonance imaging (MRI) is one of the most useful image techniques to study muscle inflammation because of its lack of ionizing radiation and the power to differentiate among various muscle abnormalities (muscle edema, fascial thickening, fatty replacement, and muscle atrophy); however, the relationship between MRI and other modalities used to examine muscle inflammation and damage has rarely been reported.

Objectives To study the relationship between the MRI findings and the creatine kinase (CK), aldolase, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels in a cohort of patients referred for suspected or confirmed muscle disease from a a single center.

Methods Patients from the Johns Hopkins Myositis Center cohort with suspected or confirmed muscle diseases were studied. Any subject with a thigh MRI and a CK, aldolase, ESR, or CRP performed within 15 days of the MRI were included in the study. For every MRI, the extent of fascial thickening, edema, fatty replacement, and atrophy were scored from 1 (<33%) to 3 (>66%) in 15 muscles of both thighs. Composite scores of the 4 MRI features were calculated summing the individual MRI scores of each of the 15 muscles of both sides. Lab values were log-transformed to allow mean comparisons (t-test) between groups and correlation (Pearson's correlation coefficient) between the lab values and the MRI features. MRI features were studied in a dichotomous fashion (yes/no) for the t-test and as continuous variables for the correlation study.

Results 462 pairs of MRI and aldolase values, 554 MRI and CK values, 346 MRI and ESR values, and 259 MRI and CRP values were studied. Aldolase, CK, and CRP were higher in those MRIs with fascial thickening and edema (all p-values <0.02). ESR was higher in those with fascial thickening (p<0.02) and of marginal significance with regard to edema (p=0.06). Aldolase and CK were higher in those MRIs with fatty replacement and atrophy (all p-values<0.05), while ESR and CRP were not significantly different (p>0.05). The edema composite score had a moderate positive correlation with levels of aldolase (rho=0.46, p<0.01) and CK (rho=0.42, p<0.01).

Conclusions MRI edema, fatty replacement, and atrophy are associated with higher CK and aldolase levels, while ESR and CRP are higher only in those MRIs with fascial thickening and edema. CK and aldolase correlate with the degree of muscle edema.

References

1. Del Grande F, Carrino JA, Del Grande M, Mammen AL, Christopher Stine L. Magnetic resonance imaging of inflammatory myopathies. Topics in magnetic resonance imaging: TMRI 2011;22(2):39-43.

2. Nakajima H, Fujiwara S, Shinoda K, Ohsawa N. Magnetic resonance imaging and serum aldolase concentration in eosinophilic fasciitis. Internal medicine 1997;36(9):654-6.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.5569