Quantitative Elastosonography of the Myotendinous Junction: Normal Behavior and Correlation With a Standard Measurement System During Functional Tests.

OBJECTIVES: In recent years, an increasing need to use imaging to assess normal and adaptive muscle function, in addition to its anatomy and structure, has emerged. We evaluated the myotendinous junction's elastosonographic behavior in light of the most recent literature on its physiologic behavior. The elastosonographic studies were compared with the results obtained from a standard measurement system to ensure a correlation with maximal muscle contraction. METHODS: Nineteen male professional soccer players were assessed during functional tests. The participants performed 5 repetitions at 60°/s to assess muscle strength and 3 repetitions at 30°/s to assess the maximum force peak of thigh muscles. The participants were monitored by a strength-power measurement system and an ultrasound machine equipped with multifrequency (18-6-MHz) linear array transducers. RESULTS: The 19 soccer players were aged between 19 and 34 years (mean age, 28 years). For the right rectus femoris, the results of the elastosonographic studies showed a mean elasticity value ± SD of 30.75% ± 10.05% with the muscle relaxed and a value of 13.75% ± 8.44% during contraction (mean decrease, 17.00% ± 11.71%). Elasticity values were 36.48% ± 8.39% before contraction and 8.77% ± 6.55% during contraction of the left rectus femoris muscle (mean decrease, 27.71% ± 11.95%). For 30° eccentric contraction of the left leg, correlation with the standard measurement system showed Pearson r values of -0.53 and -0.51 when comparing force peak and mean work, respectively, with elasticity values. CONCLUSIONS: Our study shows that strain elastosonographic quantification of muscle elasticity seems to match the expected physiologic and biomechanical behavior of the myotendinous junction.

Congenital myopathy with hanging big toe due to homozygous myopalladin (MYPN) mutation.

BACKGROUND: Myopalladin (MYPN) is a component of the sarcomere that tethers nebulin in skeletal muscle and nebulette in cardiac muscle to alpha-actinin at the Z lines. Autosomal dominant MYPN mutations cause hypertrophic, dilated, or restrictive cardiomyopathy. Autosomal recessive MYPN mutations have been reported in only six families showing a mildly progressive nemaline or cap myopathy with cardiomyopathy in some patients. CASE PRESENTATION: A consanguineous family with congenital to adult-onset muscle weakness and hanging big toe was reported. Muscle biopsy showed minimal changes with internal nuclei, type 1 fiber predominance, and ultrastructural defects of Z line. Muscle CT imaging showed marked hypodensity of the sartorius bilaterally and MRI scattered abnormal high-intensity areas in the internal tongue muscle and in the posterior cervical muscles. Cardiac involvement was demonstrated by magnetic resonance imaging and late gadolinium enhancement. Whole exome sequencing analysis identified a homozygous loss of function single nucleotide deletion in the exon 11 of the MYPN gene in two siblings. Full-length MYPN protein was undetectable on immunoblotting, and on immunofluorescence, its localization at the Z line was missed. CONCLUSIONS: This report extends the phenotypic spectrum of recessive MYPN-related myopathies showing: (1) the two patients had hanging big toe and the oldest one developed spine and hand contractures, none of these signs observed in the previously reported patients, (2) specific ultrastructural changes consisting in Z line fragmentation, but (3) no nemaline or caps on muscle pathology.