Relative basal myocardial weakness: differentiating dermatomyositis and polymyositis with cardiac involvement from viral myocarditis using speckle-tracking echocardiography and quantification of myocardial work.

Background: Both viral infection and autoimmune diseases like dermatomyositis (DM) and polymyositis (PM) can cause myocarditis and inflammatory cardiomyopathy. It is of great importance to identify underlying etiologies and initiate appropriate treatment. This study aimed to describe the pattern of regional longitudinal strain (LS) and myocardial work in PM/DM patients with cardiac involvement and investigate the usefulness of the pattern to differentiate PM/DM from acute viral myocarditis (AVM) in the clinical setting.
Methods: A total of 46 PM/DM patients with cardiac involvement, 24 patients with AVM, and 30 healthy control participants (HCs) were included. Regional myocardial work and strain analyses were performed using two-dimensional (2D) echocardiography to calculate relative basal LS and myocardial work parameters and investigate their value for differential diagnosis.
Results: PM and DM are characterized by a pattern of basal myocardial weakness with LS (basal, mid, and apical segments: -15.0±4.4, -17.1±4.7, and -21.4±6.5, respectively), myocardial work index (basal, mid, and apical segments: 1,193±432, 1,272±394, and 1,431±451, respectively), and constructive work (basal, mid, and apical segments: 1,512±422, 1,628±413, and 1,912±433, respectively) that show a base-to-apex gradient in which the myocardium at the base is more severely injured that that of the apex. On cardiovascular magnetic resonance, the positive rate of late gadolinium enhancement was also significantly higher in the basal segments (64%) than the mid (44%) and apical (28%) segments (P=0.038). A relative basal LS of 0.43, defined using the equation [average basal LS/(average mid LS + average apical LS)], had an area under curve (AUC) of 0.88 with high sensitivity (88%) and specificity (78%) to differentiate PM/DM from AVM. Using multivariate logistic regression analysis, relative basal injury of myocardium and creatine kinase elevation were strongly correlated with proximal skeletal muscle weakness according to manual muscle testing (P=0.036 and P=0.010, respectively). Conclusions: Similar to the typical proximal muscle weakness of limbs, PM/DM patients also presented with regionally decreased LS and myocardial work of the basal myocardium. A "basal weakness" pattern is easily recognizable and can be used to accurately differentiate PM/DM with cardiac involvement from AVM. 2022 Quantitative Imaging in Medicine and Surgery. All rights reserved.