Background/Purpose:

Although the prognosis of JDM has significantly improved during the past decade, some patients still experience persistent active disease, which potentially leads to irreversible damage and permanent disability. In patients with longstanding disease muscle weakness may be due to a combination of ongoing muscle inflammation, muscle atrophy, fatty replacement and steroid-induced myopathy; MRI allows to define the role of each of these components in the patients’ weakness and to overcome the limits of the clinical evaluation. The aim of this study is to estimate the frequency and distribution of muscle damage in JDM, using Whole-Body MRI (WB-MRI) and to investigate its feasibility and validity in the assessment of damage.

Methods:

WB-MRIs were obtained from 50 JDM patients (22M;28F, mean age 10.88 years, mean disease duration 3.86 years) and 50 age and sex-matched controls, using a 1.5 T MRI scanner. Muscular atrophy and fatty replacement were assessed on T1 W sequences and scored in 39 muscular groups using a 0-2 and a 0-1 point scales respectively. WB-MRI and clinical assessments were performed concurrently and the results compared. Validation procedures included analysis of reliability, construct validity and discriminative validity.

Results:

WB-MRI revealed muscle atrophy in 43/50 patients (86%) and fatty replacement in 17/50 patients (34%). Quadriceps and ileopsoas muscles were more frequently affected. The inter-reader agreement for WB-MRI scores ranged from moderate to excellent (with Cohen’s kappa ranging from 0.556-1 for the individual muscular group and intra-class correlation coefficient 0.96 for the total muscular damage score). Correlations between MDI and muscle atrophy (rs=0.4, p< 0.01) and fatty replacement (rs=0.51, p= 0.0007) were moderate and, as expected, MRI muscular damage score did not correlate with traditional measurements of disease activity. Unexpectedly, MRI damage scores did not correlate with disease duration or steroid therapy. None of controls showed signal changes in muscle revealing an excellent discriminant validity of the WB-MRI score.

WB imaging allowed to detect abnormalities in other organ and systems, including osteonecrosis   (6/50 patients, 12%), vertebral fractures (7/50, 14%) and calcinosis (14/50, 28%). Other incidental findings detected by WB MRI were a renal cyst and a thyroidal lesion which resulted to be a papillary thyroid carcinoma.

Conclusion:

WB-MRI represents a promising tool to estimate the overall spectrum of damage in JDM. An accurate discrimination between the persistent disease activity and the disease damage burden is crucial to guide treatment decision.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/whole-body-mri-a-valuable-diagnostic-tool-for-the-assessment-of-disease-damage-in-juvenile-dermatomyositis/