Advances in Quantitative Imaging of Genetic and Acquired Myopathies: Clinical Applications and Perspectives

Abstract

In the last years, magnetic resonance imaging (MRI) has become fundamental for the diagnosis and monitoring of myopathies given its ability to show the severity and distribution of pathology, to identify specific patterns of damage distribution and to properly interpret a number of genetic variants. The advances in MR techniques and post-processing software solutions have greatly expanded the potential to assess pathological changes in muscle diseases, and more specifically of myopathies; a number of features can be studied and quantified, ranging from composition, architecture, mechanical properties, perfusion, and function, leading to what is known as quantitative MRI (qMRI). Such techniques can effectively provide a variety of information beyond what can be seen and assessed by conventional MR imaging; their development and application in clinical practice can play an important role in the diagnostic process and in assessing disease course and treatment response. In this review, we briefly discuss the current role of muscle MRI in diagnosing muscle diseases and describe in detail the potential and perspectives of the application of advanced qMRI techniques in this field.

Keywords: MRI; advanced imaging; muscular imaging; myopathy; neuromuscular diseases.

Figures

Figure 1

Muscle MRI in a subset of dystrophies and congenital myopathies. For each box, thighs are displayed on the left, legs on the right side; spin-echo T1-weighted images are on top, short-tau inversion recovery (STIR) images on the bottom. (A) Child with Duchenne dystrophy (DMD) showing prominent fat replacement of gemini and adductor magnus and, to a lesser extent, of soleus, peroneal muscles, and rectus femoris bilaterally. Of note, edema of the left quadriceps and, more diffuse, of the leg muscles is evident. (B) Adult subject with Pompe Disease, showing selective fatty replacement of the posterior thigh and relative sparing of leg muscles. Slight patchy STIR hyperintensities are evident bilaterally, mainly involving the thigh musculature, as reported in literature (58). (C) Young subject with beta sarcoglycanopathy, showing important involvement of adductor magnus and longus and harmstring; at leg level the extensor digitorum longus is the most affected muscle. Unspecific slight STIR hyperintensity of the residual calf muscles is evident. (D) Young subject with Bethlem myopathy showing predominantly peripheral involvement both at the level of the thigh and leg muscles. Note the central shadow in the rectus femoris (arrow) and the bat-wing sign in the posterior leg musculature (arrowheads). No edema is evident. (E) Young subject with congenital myopathy due to selenoprotein 1 (SEPN1) showing diffuse muscular atrophy and selective fatty replacement of sartorius and, to a lesser extent, of adductor magnus; no edema is evident. (F) Young subject with facio-scapulo-humeral dystrophy (FSHD), showing involvement of the posterior thigh muscles and of tibialis anterior (TA), with sparing of the quadriceps bilaterally, but with rectus femoris involvement. Edema is evident at the level of TA and harmstring muscles and, peripherally, of vastus lateralis. All presented MRI images have been collected during routine patient care.

Figure 2

Muscle MRI in inflammatory myopathies. For each box, thighs are displayed on the left, legs on the right side; spin-echo T1-weighted images are on top, short-tau inversion recovery (STIR) images on the bottom. (A) Adult subject with polymyositis (PM), showing multifocal muscular edema involving both thigh and leg muscles and no selective pattern of fat replacement; (B) Adult subject with dermatomyositis (DM) showing characteristic multifocal perifascicular edema involving both thigh and leg muscles; (C) Adult subject with inclusion body myositis (IBM), with predominant fatty substitution of anterior thigh musculature and gemini muscles, associated to slight multifocal muscle edema. All presented MRI images have been collected during routine patient care.

Figure 3

Qualitative and quantitative left thigh muscle MRI in an adult subject with facio-scapulo-humeral disease (FSHD). (A) T1-weighted, (B) short-tau inversion recovery (STIR), and (C) fat fraction (FF) calculated with a 3-point Dixon approach are displayed. Regions-of-interest (ROI) are positioned, respectively on normal and fatty replaced muscles, with their mean FF shown as percentage in the tag. The figure shows extensive fatty replacement of the harmstring muscles (mean FF = 4%), with the ROI positioned on the long head of the biceps femoris, compared to the normal quadriceps (mean FF = 45%). Colors from dark blue to dark red represent the percentage of fat (FF) (see color bar). MRI images have been collected during routine patient care.

Figure 4

Phosphorus Magnetic Resonance Spectroscopy (31P-MRS) of a normal subject, with the voxel positioned at the level of the posterior leg muscles. The normal phosphocreatine peak is evident (Courtesy of Dr. Claudia Cinnante, Neuroradiology Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy). Image have been collected during routine patient care.

Figure 5

Heatmap of pelvic muscle involvement in disferlynopathies. The map displays the Mercuri score for all pelvic muscles in 182 subjects, also reporting the different phenotypes and the number of years in which the patient was symptomatic. Subjects are arranged (left to right) from lowest to highest mean MRI score (Courtesy of Dr. J. Diaz Manera, Neurology Service, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain). The presented heatmap is a visual representation and exemplification of the Mercuri score: the MRI conventional images used for building the heatmap have been collected for routine patient care.