Background/Purpose: In the idiopathic inflammatory myopathies (IIM) MRI imaging is traditionally focused on the proximal upper or lower extremities.  Whole body MRI (WBMRI) is a technique where the entire body is scanned into one complete study.  The purpose of this study was to assess what additional information is gained from WBMRI and to determine its relationship to clinical parameters.

Methods: 24 patients with a variety of IIM, including juvenile dermatomyositis (JDM, n=7), dermatomyositis (DM, n=6), polymyositis (PM, n=4), sporadic inclusion body myositis(s-IBM, n=3), and familial inclusion body myositis (f-IBM, n=4) underwent WBMRI.  Using a Siemens 3 Tesla MRI scanner the patients were scanned in a head to toe manner and had T1, T2, and STIR images obtained.  These images were then scored in a blinded manner across 34 muscle groups and each group was scored on a scale of 0 to 3 for T2/STIR intensity, T2/STIR area of involvement, and fatty infiltration on T1.  WBMRI and thigh MRI (THMRI) scores were evaluated for correlation with a variety of measures of disease activity and damage.

Results:

3 out of 24 patients (12.5%) who were scored to have activity (at least a 1 for STIR intensity) on WBMRI had no activity present on THMRI.  Similarly, 4 of 24 patients (16.67%) had fatty replacement on WBMRI, but no fatty replacement on THMRI.  Patients had MRI STIR abnormalities by WBMRI in many areas that would not be scanned in a MRI of the thigh or proximal arms, including the paraspinal muscles (20% of patients) and the chest (16% of patients) as well asforearms and distal extremities (Table).

Region	Percentage positive on Right	Percentage positive on Left
Anterior forearm	7.69	7.14
Posterior forearm	30.77	21.43
Distal lower extremity anterior	20.83	45.83
Distal lower extremity posterior	37.5	37.5

Among all IIM patients, physician global disease damage on a visual analogue scale (VAS) and a Likert scale correlated with imaged fatty infiltration (p<0.0001).  R squared for comparison of WBMRI and THMRI fatty replacement with physician global disease damage were 0.796 and 0.695 respectively.  Also amongst all patients serum levels of creatine kinase (CK), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) were found to correlate significantly with WBMRI STIR intensity and involvement scores, as well as with THMRI STIR intensity scores (r²=0.23-0.49, p<0.05 for all).

In adult and juvenile DM and PM patients, the physician global activity by VAS correlated with WBMRI and THMRI intensity and involvement scores (r²=0.28-0.33, p<0.05).  WBMRI and THMRI intensity and involvement scores also correlated significantly with CK, AST, ALT, and LDH (r²=0.42-0.81, p< 0.05) in this population.

Conclusion:

Conclusion:  WBMRI was able to detect areas of muscle edema and fatty infiltration in IIM patients that would not be detected on traditional focal MRI of the thighs or arms.  WBMRI also correlated well with physician assessment of disease activity and damage as well as with multiple laboratory markers of disease activity.  These findings suggest utility of WBMRI in assessing patients across the IIM spectrum.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-whole-body-versus-targeted-magnetic-resonance-imaging-for-assessing-disease-activity-and-damage-in-idiopathic-inflammatory-myopathies/