Objective: To study neuromuscular disorders by a quantitative measurement to evaluate muscle atrophy by MRI. Background The fibro-fatty replacement and myoedema are the most common indexes used to evaluate the muscle involvement in LGMD on MRI. However, many published scores are not quantitative and do not assess the extent of muscle atrophy in neuromuscular disorders. Design/Methods: We selected images obtained from T1 MRI sequences of the thigh muscles, at a distance of about 15 cm from the head of the femur. We measured the muscle area of the left quadriceps femoris and of the left vastus lateralis in 11 patients matched by sex and age, affected with 2 lipid myopathies, amyotrophic lateral sclerosis, FSHD, myofibrillar myopathy, metabolic myopathy, 2 LGMD2A, LGMD1F, localized myositis ossificans, aspecific myopathy. Results: Vastus lateralis muscle. The area was in average 963 ± 303 mm 2 . In this group of patients we have identified two subgroups, one including 5 patients with a high degree of atrophy ( high atrophic group ), whose values ranged from 400 to 900 mm 2 (mean 658.7), and one including 6 patients with a low degree of atrophy ( low atrophic group ), whose values ranged from 900 to 1400 mm 2 (mean 1217.8). Quadriceps femoris muscle in-toto. The measure of muscle area was in average 3711 ± 792 mm 2 . In the high atrophic group the values ranged from 2400 to 3400 mm 2 (mean 2966), while in the low atrophic group the values ranged from 3700 to 5000 mm 2 (mean 4332). Conclusions: Imaging examination may suggest a characteristic pattern of muscle involvement: i.e. in LGMD2A the posterior compartment is often involved. The values of cross sectional muscle area appeared to be useful indexes to evaluate muscle atrophy in LGMD, ALS and metabolic myopathies. The effect of drug treatment or of exercise or rehabilitation can be evaluated by quantitative muscle MRI. Disclosure: Dr. Angelini has received personal compensation for activities with Genzyme Corporation. Dr. Fanin has nothing to disclose. Dr. Peterle has nothing to disclose.
In a 9-year-old boy with Duchenne muscular dystrophy we found a large in-frame deletion, spanning exons 10 to 53 of the dystrophin gene. The deletion removed almost all of the central rod domain of dystrophin. Using carboxyterminal dystrophin antibodies the immunohistochemical reaction was normal in all muscle fibers. In immunoblot studies we found dystrophin of abnormal size (160 kDa) and normal amount (about 100%). The immunochemical features and the reading frame deduced from DNA analysis are usually associated with Becker muscular dystrophy, but the clinical characteristics were those of the severe Duchenne phenotype. All the cases of in-frame dystrophin deletions reported so far, which involved more than 36 exons, invariably resulted in a severe phenotype. Therefore, a threshold effect for dystrophin length may be reasonably suspected. Very short dystrophin molecules might induce a severe disarray of the dystrophin network.
Limb girdle muscular dystrophies (LGMD), a genetically and clinically heterogeneous group of neuromuscular disorders, may show gender differences in the disease severity. We aimed to measure the extent of muscle fiber atrophy and evaluate possible gender differences at fiber level.We conducted a thorough morphometric analysis of muscle fiber size and fiber area in 101 muscles from patients with various forms of LGMD (43 LGMD2A, 30 LGMD2B, 21 LGMD2C-2D-2E, 7 LGMD1C) and 12 normal controls.Reduced fiber size (atrophy) was pronounced in LGMD2A and LGMD2B, while LGMD1C showed a significant fiber hypertrophy. When we compared LGMD patients and controls of the same gender, males with LGMD2A and LGMD2B showed significantly higher fiber atrophy than control males, whereas female LGMD patients had similar values to female controls, suggesting a gender difference in muscle fiber atrophy.Less recovery to disuse atrophy in men than in women has been attributed to the possibility that in women a smaller initial muscle size associated to endocrine factors could attenuate gender-specific muscle loss. The possibility that males with LGMD may be clinically more severely affected than females has been explored, but the mechanism remains elusive.
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