Dysferlin-deficient muscular dystrophy: gadofluorine M suitability at MR imaging in a mouse model

Whole-body MRI for full assessment and characterization of diffuse inflammatory myopathy

Background

Conventional magnetic resonance imaging (MRI) is a highly valuable tool for full assessment of the extent of bilateral symmetrical diffuse inflammatory myopathy, owing to its high sensitivity in the detection of edema which correlates with, and sometimes precedes, clinical findings.

Purpose

To evaluate the use of whole-body (WB)-MRI in characterization and full assessment of the extent and distribution of diffuse inflammatory myopathy.

Material and Methods

A prospective study on 15 patients presenting with clinical evidence of inflammatory myopathy. It included 4 boys/men and 11 girls/women (age range, 6–44 years; mean age, 25.5 years). 1.5 T WB-MRI was performed and the distribution and extent of disease severity was assessed according to muscle edema on STIR images.

Results

Four cases of dermatomyositis showed lower limb disease predilection with edema in gluteal, thigh, and calf muscles. The same finding was seen in one case with recurrent polymyositis and three cases with overlap myositis with systemic lupus erythematosus (SLE). Bilateral upper and lower limb myositis was demonstrated in three cases of polymyositis and one case of overlap myositis with scleroderma. Bilateral edema involving all scanned muscle groups was detected in three cases of polymyositis with paraneoplastic syndrome, SLE, and severe active dermatomyositis (including the neck muscles).

Conclusion

WB-MRI is the diagnostic modality of choice for cases of inflammatory myopathy. It accurately detects the most severely affected muscles candidate for biopsy and provides a reliable baseline study for follow-up of disease progression as well as response to treatment.

7-Tesla magnetic resonance imaging precisely and noninvasively reflects inflammation and remodeling of the skeletal muscle in a mouse model of antisynthetase syndrome

Inflammatory myopathies comprise heterogeneous disorders. Their etiopathogenesis is poorly understood, because of the paucity of informative experimental models and of approaches for the noninvasive study of inflamed tissues. Magnetic resonance imaging (MRI) provides information about the state of the skeletal muscle that reflects various facets of inflammation and remodeling. This technique has been scarcely used in experimental models of inflammatory myopathies. We characterized the performance of MRI in a well-established mouse model of myositis and the antisynthetase syndrome, based on the immunization of wild-type mice with the amino-terminal fragment of histidyl-tRNA synthetase (HisRS). Over an eight-week period following myositis induction, MRI enabled precise identification of pathological events taking place in muscle tissue. Areas of edema and of active inflammation identified by histopathology paralleled muscle modifications detected noninvasively by MRI. Muscles changes were chronologically associated with the establishment of autoimmunity, as reflected by the development of anti-HisRS antibodies in the blood of immunized mice. MR imaging easily appreciated muscle damage and remodeling even if actual disruption of myofiber integrity (as assessed by serum concentrations of creatinine phosphokinase) was limited. Thus, MR imaging represents an informative and noninvasive analytical tool for studying in vivo immune-mediated muscle involvement.

Analysis of fatty infiltration and inflammation of the pelvic and thigh muscles in boys with Duchenne muscular dystrophy (DMD): grading of disease involvement on MR imaging and correlation with clinical assessments

BACKGROUND

Prior reports focus primarily on muscle fatty infiltration in Duchenne muscular dystrophy (DMD). However, the significance of muscle edema is uncertain.

OBJECTIVE

To evaluate the frequency and degree of muscle fat and edema, and correlate these with clinical function.

MATERIALS AND METHODS

Forty-two boys (ages 5-19 years) with DMD underwent pelvic MRI. Axial T1- and fat-suppressed T2-weighted images were evaluated to grade muscle fatty infiltration (0-4) and edema (0-3), respectively. Degree and frequency of disease involvement were compared to clinical evaluations.

RESULTS

Gluteus maximus had the greatest mean fatty infiltration score, followed by adductor magnus and gluteus medius muscles, and had the most frequent and greatest degree of fatty infiltration. Gluteus maximus also had the greatest mean edema score, followed by vastus lateralis and gluteus medius muscles. These muscles had the most frequent edema, although the greatest degree of edema was seen in other muscles. There was correlation between cumulative scores of fatty infiltration and all clinical evaluations (P < 0.05).

CONCLUSION

In DMD, the muscles with the most frequent fatty infiltration had the greatest degree of fatty infiltration and correlated with patient function. However, the muscles with the most frequent edema were different from those with the greatest degree of edema. Thus, edema may not predict patient functional status.

Temporal changes in magnetic resonance imaging in the mdx mouse

Background

Duchenne muscular dystrophy (DMD) is characterized clinically by severe, progressive loss of skeletal muscle. The phenotype is much less severe in the mdx mouse model of DMD than that seen in patients with DMD. However, a “critical period” has been described for the mdx mouse, during which there is a peak in muscle weakness and degeneration/regeneration between the 2^nd and 5^th weeks of life. A number of studies have employed small animal magnetic resonance imaging (MRI) to examine skeletal muscle in various dystrophic models, but such studies represent a snapshot in time rather than a longitudinal view.

Results

The in vivo cross-sectional T₂-weighted image of the healthy (wild type, WT) muscles is homogeneously dark and this homogeneity does not change with time, as there is no disease. We, and others, have shown marked changes in MRI in dystrophic muscle, with multiple, unevenly distributed focal hyperintensities throughout the bulk of the muscles. Here we monitored an mdx mouse using MRI from 5 to 80 weeks of age. Temporal MRI scans show an increase in heterogeneity shortly after the critical period, at 9 and 13 weeks of age, with a decrease in heterogeneity thereafter. The 4.3-fold increase in percent heterogeneity at week 9 and 13 is consistent with the notion of an early critical period described for mdx mice.

Conclusions

Age is a significant variable in quantitative MR studies of the mdx mouse. The mdx mouse is typically studied during the critical period, at a time that most closely mimics the DMD pathology, but the preliminary findings here, albeit based on imaging only one mdx mouse over time, suggest that the changes in MRI can occur shortly after this period, when the muscles are still recovering.

Assessment of disease activity in muscular dystrophies by noninvasive imaging

Muscular dystrophies are a class of disorders that cause progressive muscle wasting. A major hurdle for discovering treatments for the muscular dystrophies is a lack of reliable assays to monitor disease progression in animal models. We have developed a novel mouse model to assess disease activity noninvasively in mice with muscular dystrophies. These mice express an inducible luciferase reporter gene in muscle stem cells. In dystrophic mice, muscle stem cells activate and proliferate in response to muscle degeneration, resulting in an increase in the level of luciferase expression, which can be monitored by noninvasive, bioluminescence imaging. We applied this noninvasive imaging to assess disease activity in a mouse model of the human disease limb girdle muscular dystrophy 2B (LGMD2B), caused by a mutation in the dysferlin gene. We monitored the natural history and disease progression in these dysferlin-deficient mice up to 18 months of age and were able to detect disease activity prior to the appearance of any overt disease manifestation by histopathological analyses. Disease activity was reflected by changes in luciferase activity over time, and disease burden was reflected by cumulative luciferase activity, which paralleled disease progression as determined by histopathological analysis. The ability to monitor disease activity noninvasively in mouse models of muscular dystrophy will be invaluable for the assessment of disease progression and the effectiveness of therapeutic interventions.

Long-term assessment of contrast effects of gadofluorine M and gadofluorine P in magnetic resonance imaging of mice

PURPOSE

To investigate the long-term time course of the contrast effects after the intravenous injection of gadofluorine M or gadofluorine P in mice.

MATERIALS AND METHODS

Magnetic resonance images were acquired longitudinally after intravenous injection of 0.1 μmol Gd/g gadofluorine M into BALB/c mice. The contrast effects were also assessed in C57BL/6J mice injected with gadofluorine M, BALB/c mice injected with gadofluorine P, and BALB/c mice injected with a double dose of gadopentetate dimeglumine.

RESULTS

The injection of gadofluorine M into BALB/c mice caused prolonged contrast effects in the blood and other organs. The liver enhancement was especially long-lasting and still evident 6 days after injection. Strain-related differences in contrast kinetics of gadofluorine M were not observed between BALB/c mice and C57BL/6J mice. In comparison with gadofluorine M, clearances from the blood, liver, and kidney were more rapid and contrast enhancement in the spleen was generally lower for gadofluorine P. The enhancement in the gallbladder cavity, indicating biliary excretion, was evident only after gadofluorine P injection. Blood enhancement at 10 min was much weaker for gadopentetate dimeglumine.

CONCLUSION

Both gadofluorine M and gadofluorine P appear to be applicable to blood pool imaging and liver imaging in mice.

Gadofluorine M-enhanced MRI shows involvement of circumventricular organs in neuroinflammation

Background

Circumventricular organs (CVO) are cerebral areas with incomplete endothelial blood-brain barrier (BBB) and therefore regarded as "gates to the brain". During inflammation, they may exert an active role in determining immune cell recruitment into the brain.

Methods

In a longitudinal study we investigated in vivo alterations of CVO during neuroinflammation, applying Gadofluorine M- (Gf) enhanced magnetic resonance imaging (MRI) in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. SJL/J mice were monitored by Gadopentate dimeglumine- (Gd-DTPA) and Gf-enhanced MRI after adoptive transfer of proteolipid-protein-specific T cells. Mean Gf intensity ratios were calculated individually for different CVO and correlated to the clinical disease course. Subsequently, the tissue distribution of fluorescence-labeled Gf as well as the extent of cellular inflammation was assessed in corresponding histological slices.

Results

We could show that the Gf signal intensity of the choroid plexus, the subfornicular organ and the area postrema increased significantly during experimental autoimmune encephalomyelitis, correlating with (1) disease severity and (2) the delay of disease onset after immunization. For the choroid plexus, the extent of Gf enhancement served as a diagnostic criterion to distinguish between diseased and healthy control mice with a sensitivity of 89% and a specificity of 80%. Furthermore, Gf improved the detection of lesions, being particularly sensitive to optic neuritis. In correlated histological slices, Gf initially accumulated in the extracellular matrix surrounding inflammatory foci and was subsequently incorporated by macrophages/microglia.

Conclusion

Gf-enhanced MRI provides a novel highly sensitive technique to study cerebral BBB alterations. We demonstrate for the first time in vivo the involvement of CVO during the development of neuroinflammation.

Neuromuscular imaging in inherited muscle diseases

Driven by increasing numbers of newly identified genetic defects and new insights into the field of inherited muscle diseases, neuromuscular imaging in general and magnetic resonance imaging (MRI) in particular are increasingly being used to characterise the severity and pattern of muscle involvement. Although muscle biopsy is still the gold standard for the establishment of the definitive diagnosis, muscular imaging is an important diagnostic tool for the detection and quantification of dystrophic changes during the clinical workup of patients with hereditary muscle diseases. MRI is frequently used to describe muscle involvement patterns, which aids in narrowing of the differential diagnosis and distinguishing between dystrophic and non-dystrophic diseases. Recent work has demonstrated the usefulness of muscle imaging for the detection of specific congenital myopathies, mainly for the identification of the underlying genetic defect in core and centronuclear myopathies. Muscle imaging demonstrates characteristic patterns, which can be helpful for the differentiation of individual limb girdle muscular dystrophies. The aim of this review is to give a comprehensive overview of current methods and applications as well as future perspectives in the field of neuromuscular imaging in inherited muscle diseases. We also provide diagnostic algorithms that might guide us through the differential diagnosis in hereditary myopathies.

T2 mapping in Duchenne muscular dystrophy: distribution of disease activity and correlation with clinical assessments

PURPOSE

To analyze T2 maps of pelvic and thigh muscles in Duchenne muscular dystrophy (DMD), to identify the most severely affected muscle, and to correlate the T2 of muscle with the grade of fatty infiltration at nonquantitative magnetic resonance (MR) imaging and results of clinical assessment.

MATERIALS AND METHODS

This prospective study was HIPAA compliant and was approved by the institutional review board; written consent was obtained from all participants' parents or guardians. Thirty-four boys with DMD (mean age, 8.4 years) were evaluated clinically (age, clinical function score, timed Gower score, time to run 30 feet, and serum creatine kinase [CK] level) and with nonquantitative MR imaging and axial T2 mapping from the iliac crest to the mid thigh. The T2 maps and mean T2 of 18 muscles in the pelvis and thighs were analyzed to identify the most severely involved muscle. The amount of fatty infiltration was assigned a grade of zero to four for all pelvic and thigh muscles by using T1-weighted nonquantitative MR images. The Spearman correlation coefficients model was used to correlate the mean T2, nonquantitative MR imaging score and clinical assessments.

RESULTS

The gluteus maximus muscle had the highest T2. The mean T2 for this muscle showed a significant correlation with the nonquantitative MR imaging score for fatty infiltration (P < .001) and with all clinical assessments except CK level.

CONCLUSION

Gluteus maximus muscles are most severely affected in patients with DMD. The T2 of the gluteus maximus muscle can be used as a quantitative and objective measure of disease severity.