First pilot study of extracellular volume MRI measurement in peripheral muscle of systemic sclerosis patients suggests diffuse fibrosis

Objectives

Peripheral muscle involvement in systemic sclerosis (SSc) may comprise myositis or a non-inflammatory myopathy. There is little understanding on the nature of SSc myopathy. This pilot study aimed to evaluate for the presence of diffuse fibrosis in the peripheral muscle of patients with SSc by determining extracellular volume (ECV) MRI measurement.

Methods

SSc patients, with suspected myopathy or no muscle involvement, and healthy volunteers (HV) had native T1 and ECV MRI quantification of the thigh and creatine-kinase (CK) measured. Suspected myopathy was defined as current/history of minimally raised CK (<600 IU/l) +/- presence of clinical signs-symptoms (proximal muscle weakness and/or myalgia) +/- a Manual Muscle Testing score <5 in the thighs.

Results

12 SSc patients and 10 HV were recruited. 9/12 patients had limited cutaneous SSc, 4/12 interstitial lung disease, 7/12 suspected myopathy. Higher skeletal muscle ECV was recorded in SSc patients compared to HV [mean (SD) 23(11)%, vs 11(4)% p = 0.04].

Peripheral muscle ECV associated with CK (rho=0.554, p = 0.061) and was higher in SSc patients with myopathy compared to those with no myopathy [mean (SD) 28 (10) vs 15 (5), p = 0.023]. An ECV of 22% was determined to best identify myopathy with a sensitivity of 71% and a specificity of 80%.

Conclusion

This hypothesis-generating study showed higher ECV in SSc patients compared to HV as well as association of ECV with suspected myopathy, suggesting the presence of diffuse fibrosis in the peripheral muscle of SSc patients. Further studies are needed to understand the nature of SSc myopathy.