Usefulness and Clinical Impact of Whole-Body MRI in Detecting Autoimmune Neuromuscular Disorders

Abstract

Autoimmune neuromuscular diseases are a group of heterogenous pathologies secondary to the activation of the immune system that damage the structures of the peripheric nerve, the neuromuscular junction, or the skeleton muscle. The diagnosis of autoimmune neuromuscular disorders comprises a combination of data from clinical, laboratory, electromyography, imaging exam, and biopsy. Particularly, the whole-body MRI examination in the last two decades has been of great use in the assessment of neuromuscular disorders. MRI provides information about the structures involved and the status of activity of the disease. It can also be used as a biomarker, detect the pattern of specific muscle involvement, and is a useful tool for targeting the optimal muscle site for biopsy. In this work, we summarized the most used technical protocol of whole-body MRI and the role of this imaging technique in autoimmune neuromuscular disorders.

Keywords: AIDP; CIDP; Lambert–Eaton; autoimmune neuromuscular disorder; focal myositis; idiopathic inflammatory myopathies; myasthenia gravis; whole-body MRI.

Figure 1

Coronal composite views generated by combining the series of coronal T1-weighted and STIR images. (A–C) Coronal compositive view, T1-weighted, sliding anterior to posterior side, respectively. (D–F) Coronal compositive view, STIR, sliding anterior to posterior side, respectively.

Figure 2

T1-weighted DIXON sequences of the posterior part of the thighs. (A) Fat-only coronal image. (B) Water-only coronal image. (C) Coronal T1-weighted in phase image. (D) Coronal T1-weighted out-phase image. (E) Coronal fat fraction map; the sites of ROIs: one in the muscular belly of the long head of the right biceps femoris; the other in the subcutaneous fat.

Figure 3

Schematic drawing of pattern edema. (A) Normal appearance of the muscle belly. (B) Diffuse end homogeneous edema. (C) “Foggy” edema. (D) Focal, “patchy” edema. (E) Subfascial and interfascicular edema with reticular or “honeycombing” appearance. (F) Subcutaneous and subfascial edema.

Figure 4

Schematic drawing of Mercuri’s classification of fatty atrophy grade. (A) Grade 0: Normal appearance of the muscle belly. (B) Grade 1: Early moth-eaten appearance with scattered small areas of fatty replacement. (C) Grade 2a: Late moth-eaten appearance, with numerous areas of fatty replacement with beginning confluence comprising less than 30%. (D) Grade 2b: Late moth-eaten appearance, with numerous areas of fatty replacement, with beginning confluence comprising 30–60%. (E) Grade 3: Washed-out, fuzzy appearance due to confluent areas of fatty replacement, with muscle still present at the periphery. (F) Grade 4: End-stage appearance, all muscle replaced by fat with complete fatty replacement.

Figure 5

Example atrophy with fatty replacement using Mercuri’s classification. (A) Grade 0: All the muscles have regular intensity on T1-weighted imaging. (B) Grade 1: Fatty atrophy of semimembranosus (yellow arrowhead) and biceps femoris (white arrowhead), showing early moth-eaten appearance with scattered small areas of high signal on T1-weighted imaging. (C) Grade 2a: Fatty atrophy of semimembranosus (yellow arrowhead) and biceps femoris (white arrowhead), showing late moth-eaten appearance, with numerous areas of high signal on T1-weighted imaging, with beginning confluence comprising less than 30%. (D) Grade 2b: Fatty atrophy of semimembranosus (yellow arrowhead) and sartorius (white arrowhead), showing late moth-eaten appearance, with numerous areas of high signal on T1-weighted image, with beginning confluence comprising 30–60%. (E) Grade 3: Fatty atrophy of rectus femoris (yellow arrowhead) and vastus lateralis and vastus intermedius (white arrowhead), showing a fuzzy appearance due to confluent areas of high signal on T1-weighted imaging, with muscle still present at the periphery. (F) Grade 4: Fatty atrophy of vastus intermedius (white arrowhead); all muscle replaced by fat shows a homogeneous high signal on T1-weighted imaging.

Figure 6

MRI of a patient with immune-mediated necrotizing myopathy with hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies positivity. (A) Coronal STIR image reveals a bilateral diffuse high intensity of adductors muscles (white arrow), and of the vasti muscle of the quadriceps femoris (with arrowhead). (B) Axial STIR image shows a bilateral and diffuse high intensity of the gluteus maximum muscle (black arrow), of the adductor muscles (white arrow), of the tensor of fascia lata (yellow arrowhead), and the right rectus femoris muscle (white arrowhead). (C) Axial STIR image shows bilateral involvement of the adductor muscles (white arrow), the hamstring muscles (black arrow), and the vasti muscle and rectus femoris of the right quadriceps femoris muscle (white arrowhead).