Résumé :
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Mutations of TPM2, a gene coding for tropomyosin 2, have been identified in patients with nemalin myopathy or CAPs disease. Using whole-body (WB) MRI, we determined the patterns of muscle involvement in patients with TPM2 mutations. Materials and methods. Eight individuals belonging to 5 different families were examined (6 patients and 2 pauci-symptomatic relatives). All carried at least one mutation in TPM2 gene. Muscle biopsy, performed in 5 subjects, showed rods (3/5), "caps disease" (1/5) and non specific myopathy (1/5). The patients presented early onset and variable clinical features with two main patterns (predominant weakness or joint and spinal stiffness). The child with CAPs disease had marked facial-ocular involvement (pseudomyasthenic) and was mechanically ventilated via tracheotomy. All were ambulatory. WB imaging was performed on a 1.5T MR system using parallel imaging. Examination time was 43 min. Coronal and axial T1-weighted (T1w) and coronal short tau inversion recovery (STIR) sequences were acquired. Images were analysed using the Lamminen-Mercuri classification (4 grades from1 normal to 4 total fatty replacement). Results. On T1w images, leg muscles were always affected (8/8; average score 2.3) : gastrocnemius lateralis (4/8; 2), gastrocnemius medialis (4/8; 2), soleus (8/8; 2.5), tibialis anterior (5/8; 2.8), tibialis posterior (3/8; 2.3), extensor digitorum (4/8; 2.3), flexor digitorum (3/8; 2,3) and peroneus (3/8; 2). Cephalic muscles were often affected (6/8; 2.1) involving temporal (6/8; 2), masseter (3/8; 2.2), pterygoid medial (3/8; 2) and lateral (3/8; 2) heads. Thigh lesions (6/8; 2.4) concerned rectus femoris (4/8; 2.5), vasti lateralis (3/8; 2.3), medialis (1/8; 3), intermedialis (2/8; 2.5), gracilis (1/8; 3), sartorius (1/8; 2), semi membranous (3/8; 2.7). Shoulder, arm and forearm muscles were relatively spared (2/8; 2), with degenerative changes occasionally seen in deltoid (1/8; 2), subscapularis (1/8; 2), anterior arm compartement (1/8; 2), posterior arm compartment (1/8; 2). STIR sequences were normal. Conclusion. While being caused by different gene mutations and although associated with a variety of clinical presentations, most TPM2 myopathies and clinically silent mutations shared a particular muscle involvement including temporal muscles in the head and distal muscles in the lower extremities. This pattern might be exploited in order to facilitate the differential diagnosis as well as to guide muscle biopsy.
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