Comparison of muscle magnetic resonance imaging data with clinical and laboratory parameters in follow-up of patients with idiopathic inflammatory myopathy

During dynamic follow-up of patients with idiopathic inflammatory myopathy (IIM), changes in disease activity and damage caused are assessed using several generally recognized instruments. In parallel, objective methods of visualization are used, in particular magnetic resonance imaging (MRI) of the muscles. Currently, the relationship between the results of MRI and clinical and laboratory parameters in dynamics is not well studied. Objective: to evaluate the main signs of muscle involvement using MRI in dynamics and to compare them with clinical and laboratory parameters, activity indices and damage in patients with IIM. Material and methods. The study included 32 patients with diseases from the group of IIM that met the EULAR/ACR 2017 classification criteria. All patients underwent MRI of the hip and calf muscles twice on the Philips Multiva 1.5 Tesla (Philips, The Netherlands) employing T1, T2, and STIR-T2 sequences, signs of oedema and fatty remodeling were assessed on a 4-point semiquantitative scale. The median time between examinations was 15.5 [9; 24] months. A standard clinical examination, including a manual muscle test (MMT-8), was performed at the initial and the second examinations of the patients. Disease activity was determined using the MITAX index and irreversible changes were assessed using the MDI damage index. Results and discussion. During follow-up a statistically significant decrease in total oedema score and an increase in total fatty remodeling score in the thighs and calves was observed (p<0.05). The decrease in oedema total score in the thighs was associated with an increase in muscle strength according to the results of the MMT-8 (p=0.03), a decrease in creatine phosphokinase level (CPK; p=0.005) and activity index (p=0.003). The increase in the total thigh fatty replacement score was associated with a decrease in muscle strength according to the MMT-8 (p=0.01) and an increase in irreversible muscle changes according to the damage index (p=0.002). A decrease in total calves oedema score was associated with a decrease in CPK level (p=0.002) and activity index (p<0.001). A change in the total calves fatty replacement score was not associated with statistically significant changes in clinical and laboratory parameters of the disease. Conclusion. Changes in the main signs of muscle involvement, oedema and fatty replacement, according to MRI showed a clear parallelism with the dynamics of clinical and laboratory indicators, which confirms the sensitivity of this method to changes in both the activity and severity of the disease. Thus, MRI of muscles in patients with muscle weakness makes it possible to distinguish the signs of inflammation from the manifestations of irreversible damage, which is of great importance for determining treatment tactics and prognosis.