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OBJECTIVE - Decreased radiodensity of adipose tissue (AT) located in the visceral AT (VAT), subcutaneous AT (SAT), and intermuscular AT (IMAT) abdominal depots is associated with hyperglycemia, hyperinsulinemia, and insulin resistance independent of AT volumes. These associations were sought in African-ancestry men, who have higher risk for type 2 diabetes and have been underrepresented in previous studies.
METHODS - This cross-sectional analysis included 505 nondiabetic men of African-Caribbean ancestry (median age: 61 years; median BMI: 26.8 kg/m ) from the Tobago Health Study. AT volumes and radiodensities were assessed using computed tomography, including abdominal (VAT and SAT) and thigh (IMAT) depots. Associations between AT radiodensities were assessed with fasting serum glucose and insulin and with insulin resistance (updated homeostatic model assessment of insulin resistance, HOMA2-IR).
RESULTS - Higher radiodensity in any AT depot was associated with lower log-insulin and log-HOMA2-IR (β range: -0.16 to -0.18 for each; all P < 0.0001). No AT radiodensity was associated with glucose. Thigh IMAT radiodensity associations were independent of, and similar in magnitude to, VAT radiodensities. Model fit statistics suggested that AT radiodensities were a better predictor for insulin and insulin resistance compared with AT volumes in individuals with overweight and obesity.
CONCLUSIONS - AT radiodensities at multiple depots are significantly associated with insulin and insulin resistance in African-ancestry men.
© 2019 The Obesity Society.
Quantitative magnetization transfer (qMT) imaging in skeletal muscle may be confounded by intramuscular adipose components, low signal-to-noise ratios (SNRs), and voluntary and involuntary motion artifacts. Collectively, these issues could create bias and error in parameter fitting. In this study, technical considerations related to these factors were systematically investigated, and solutions were proposed. First, numerical simulations indicate that the presence of an additional fat component significantly underestimates the pool size ratio (F). Therefore, fat-signal suppression (or water-selective excitation) is recommended for qMT imaging of skeletal muscle. Second, to minimize the effect of motion and muscle contraction artifacts in datasets collected with a conventional 14-point sampling scheme, a rapid two-parameter model was adapted from previous studies in the brain and spinal cord. The consecutive pair of sampling points with highest accuracy and precision for estimating F was determined with numerical simulations. Its performance with respect to SNR and incorrect parameter assumptions was systematically evaluated. QMT data fitting was performed in healthy control subjects and polymyositis patients, using both the two- and five-parameter models. The experimental results were consistent with the predictions from the numerical simulations. These data support the use of the two-parameter modeling approach for qMT imaging of skeletal muscle as a means to reduce total imaging time and/or permit additional signal averaging.
Copyright © 2015 Elsevier Inc. All rights reserved.
OBJECTIVES - It is unknown whether muscle wasting accounts for impaired physical function in adults on maintenance hemodialysis (MHD).
DESIGN - Observational study.
SETTING - Outpatient dialysis units and a fall clinic.
SUBJECTS - One hundred eight MHD and 122 elderly nonhemodialysis (non-HD) participants.
EXPOSURE VARIABLE - Mid-thigh muscle area was measured by magnetic resonance imaging.
MAIN OUTCOME MEASURE - Physical function was measured by distance walked in 6 minutes.
RESULTS - Compared with non-HD elderly participants, MHD participants were younger (49.2 ± 15.8 vs. 75.3 ± 7.1 years; P < .001) and had higher mid-thigh muscle area (106.2 ± 26.8 vs. 96.1 ± 21.1 cm2; P = .002). However, the distance walked in 6 minutes was lower in MHD participants (322.9 ± 110.4 vs. 409.0 ± 128.3 m; P < .001). In multiple regression analysis adjusted for demographics, comorbid conditions, and mid-thigh muscle area, MHD patients walked significantly less distance (-117 m; 95% confidence interval: -177 to -56 m; P < .001) than the non-HD elderly.
CONCLUSIONS - Even when compared with elderly non-HD participants, younger MHD participants have poorer physical function that was not explained by muscle mass or comorbid conditions. We speculate that the uremic milieu may impair muscle function independent of muscle mass. The mechanism of impaired muscle function in uremia needs to be established in future studies.
Published by Elsevier Inc.
OBJECTIVE - To investigate the association of low-density (lipid-rich) muscle measured by computed tomography (CT) with skeletal muscle function and health-related quality of life in idiopathic inflammatory myopathies (IIMs).
METHODS - Seventeen patients and 10 healthy controls underwent CT of the midthigh to quantify high- (30-100 HU) and low-density (0-29 HU) skeletal muscle areas. Anthropometric measures, body composition, physical activity level, health-related quality of life, skeletal muscle strength, endurance, and fatigue were assessed. Patients were compared against controls. The relationship of anthropometric, body composition, and disease variables with measures of muscle function were examined using Spearman's test on the patient group. Linear regression was used to assess the age- and disease-adjusted relationship of muscle quality to physical function and muscle strength.
RESULTS - Patients had higher body fat percentage (P = 0.042), trunk fat mass (P = 0.042), android:gynoid fat (P = 0.033), and midthigh low-density muscle/total muscle area (P < 0.001) compared to controls. Midthigh low-density muscle/total muscle area was negatively correlated with self-reported physical function, strength, and endurance (the Short Form 36 [SF-36] health survey physical functioning [P = 0.004], manual muscle testing [P = 0.020], knee maximal voluntary isometric contraction/thigh mineral-free lean mass [P < 0.001], and the endurance step test [P < 0.001]), suggesting that muscle quality impacts function in IIM. Using multiple linear regression adjusted for age, global disease damage, and total fat mass, poor muscle quality as measured by midthigh low-density muscle/total muscle area was negatively associated with SF-36 physical functioning (P = 0.009).
CONCLUSION - Midthigh low-density muscle/total muscle area is a good predictor of muscle strength, endurance, and health-related quality of life as it pertains to physical functioning in patients with IIMs.
© 2015, American College of Rheumatology.
PURPOSE - Using three separate models that included total body mass, total lean and total fat mass, and abdominal and thigh fat as independent measures, we determined their association with knee joint loads in older overweight and obese adults with knee osteoarthritis (OA).
METHODS - Fat depots were quantified using computed tomography, and total lean and fat mass were determined with dual energy x-ray absorptiometry in 176 adults (age, 66.3 yr; body mass index, 33.5 kg·m) with radiographic knee OA. Knee moments and joint bone-on-bone forces were calculated using gait analysis and musculoskeletal modeling.
RESULTS - Higher total body mass was significantly associated (P ≤ 0.0001) with greater knee compressive and shear forces, compressive and shear impulses (P < 0.0001), patellofemoral forces (P < 0.006), and knee extensor moments (P = 0.003). Regression analysis with total lean and total fat mass as independent variables revealed significant positive associations of total fat mass with knee compressive (P = 0.0001), shear (P < 0.001), and patellofemoral forces (P = 0.01) and knee extension moment (P = 0.008). Gastrocnemius and quadriceps forces were positively associated with total fat mass. Total lean mass was associated with knee compressive force (P = 0.002). A regression model that included total thigh and total abdominal fat found that both were significantly associated with knee compressive and shear forces (P ≤ 0.04). Thigh fat was associated with knee abduction (P = 0.03) and knee extension moment (P = 0.02).
CONCLUSIONS - Thigh fat, consisting predominately of subcutaneous fat, had similar significant associations with knee joint forces as abdominal fat despite its much smaller volume and could be an important therapeutic target for people with knee OA.
Muscle diseases commonly have clinical presentations of inflammation, fat infiltration, fibrosis, and atrophy. However, the results of existing laboratory tests and clinical presentations are not well correlated. Advanced quantitative MRI techniques may allow the assessment of myo-pathological changes in a sensitive and objective manner. To progress towards this goal, an array of quantitative MRI protocols was implemented for human thigh muscles; their reproducibility was assessed; and the statistical relationships among parameters were determined. These quantitative methods included fat/water imaging, multiple spin-echo T2 imaging (with and without fat signal suppression, FS), selective inversion recovery for T1 and quantitative magnetization transfer (qMT) imaging (with and without FS), and diffusion tensor imaging. Data were acquired at 3.0 T from nine healthy subjects. To assess the repeatability of each method, the subjects were re-imaged an average of 35 days later. Pre-testing lifestyle restrictions were applied to standardize physiological conditions across scans. Strong between-day intra-class correlations were observed in all quantitative indices except for the macromolecular-to-free water pool size ratio (PSR) with FS, a metric derived from qMT data. Two-way analysis of variance revealed no significant between-day differences in the mean values for any parameter estimate. The repeatability was further assessed with Bland-Altman plots, and low repeatability coefficients were obtained for all parameters. Among-muscle differences in the quantitative MRI indices and inter-class correlations among the parameters were identified. There were inverse relationships between fractional anisotropy (FA) and the second eigenvalue, the third eigenvalue, and the standard deviation of the first eigenvector. The FA was positively related to the PSR, while the other diffusion indices were inversely related to the PSR. These findings support the use of these T1 , T2 , fat/water, and DTI protocols for characterizing skeletal muscle using MRI. Moreover, the data support the existence of a common biophysical mechanism, water content, as a source of variation in these parameters.
Copyright © 2014 John Wiley & Sons, Ltd.
PURPOSE - To compare the precision of measuring the pennation angle and fiber length in the vastus lateralis (VL) using two distinctly different diffusion tensor imaging (DTI) sequences.
MATERIALS AND METHODS - We imaged the thigh of 10 normal subjects on a 3T magnetic resonance (MR) imager with twice refocused spin echo (TRSE) and stimulated echo (STEAM) DTI-MRI techniques. Both techniques took the same total acquisition time and employed the same diffusion weighting and gradient directions. Using the diffusion tensor images produced by each sequence, muscle fiber bundles were tracked from the aponeurosis by following the first eigenvector of the diffusion tensor. From these tracks we calculated the pennation angle and fiber length.
RESULTS - The STEAM acquisition resulted in significantly higher signal-to-noise ratio (SNR), lower apparent diffusion coefficient (ADC), higher fractional anisotropy (FA) values, and longer fibers than TRSE. Although no difference in the pennation angle between the two acquisitions was found, the TRSE sequence had a significantly greater within-subject dispersion in the pennation angle of tracked fibers, which may indicate a reduction in the coherence of fiber bundles.
CONCLUSION - DTI of muscle using a STEAM acquisition resulted in significant improvements in the SNR and FA, resulting in tracking a larger number of muscle fiber bundles over longer distances and with less within-subject dispersion.
© 2014 Wiley Periodicals, Inc.
BACKGROUND - In a recent study designed to determine the anatomic location of infection in children presenting with acute hip pain, fever, and elevated inflammatory markers, we demonstrated the incidence of infection of the musculature surrounding the hip to be greater than twice that of septic arthritis. Importantly, the obturator musculature was infected in >60% of cases. Situated deep in the pelvis, surrounding the obturator foramen, debridement of these muscles and placement of a drain traditionally requires an extensive ilioinguinal or Pfannenstiel approach, placing significant risk to the surrounding neurovascular structures. We hypothesized that the obturator internus and externus could be successfully debrided using a limited medial approach.
METHODS - An IRB-approved prospective study of children (0 to 18 y) evaluated in the pediatric emergency department by an orthopaedic surgeon to rule out septic hip arthritis at a tertiary care children's hospital (July 1, 2010 to June 30, 2012) was conducted. Infected obturator musculature was identified and confirmed using magnetic resonance imaging. Cadaveric dissection was performed comparing the ilioinguinal, Pfannenstiel, and proposed minimally invasive medial approach. The proposed approach was utilized to debride and place drains in 7 consecutive patients.
RESULTS - Anatomic information gained from magnetic resonance images of patients with abscess within the obturator musculature, and from the results of cadaveric studies, allowed for planning of a novel surgical approach. We found that through the surgical approach used to perform an osteotomy of the ischium (Tonnis) the obturator externus could be debrided through the adductor brevis and the obturator internus could be debrided through the obturator foramen. Using our medial approach, resolution of symptoms in all children who underwent surgical drainage resulted without complication.
CONCLUSIONS - Our medial approach can safely access the obturator musculature for abscess decompression and drain placement with successful results. Advantages to this approach include: lower risk to neurovascular structures within the pelvis, less soft tissue trauma, and similarity to current techniques used for adductor lengthening, medial reduction of the dislocated hip, and osteotomy of the ischium.
LEVEL OF EVIDENCE - Level II.
Benign metastasizing leiomyoma, a rare condition of controversial origin, is characterized by the occurrence of extrauterine smooth muscle tumors primarily affecting the lungs of women with a history of uterine leiomyomas. Numerous genetic studies of uterine leiomyoma with rearrangements of the HMGA2 and HMGA1 loci defined in prominent subgroups have been conducted. In contrast, cytogenetic and molecular descriptions of benign metastasizing leiomyoma are few, and, in particular, this entity has not been previously subjected to single nucleotide polymorphism (SNP) array analysis. In this study, conventional karyotypic, and/or molecular cytogenetic, and SNP array characterization of a pleuropulmonary benign mestasizing leiomyoma and a synchronous deep soft tissue leiomyoma of the thigh, which arose in a 56-year-old female with a remote history of uterine leiomyomata, revealed rearrangement of the HMGA1 (6p21) locus and nearly identical genomic profiles, including loss of chromosome 7 material in both lesions. These findings suggest that both the deep soft tissue and pleuropulmonary lesions were derived from the same abnormal clone and are genetically related to uterine leiomyomata.
Copyright © 2012 Elsevier Inc. All rights reserved.
Age-related increases in ectopic fat accumulation are associated with greater risk for metabolic and cardiovascular diseases, and physical disability. Reducing skeletal muscle fat and preserving lean tissue are associated with improved physical function in older adults. PPARγ-agonist treatment decreases abdominal visceral adipose tissue (VAT) and resistance training preserves lean tissue, but their effect on ectopic fat depots in nondiabetic overweight adults is unclear. We examined the influence of pioglitazone and resistance training on body composition in older (65-79 years) nondiabetic overweight/obese men (n = 48, BMI = 32.3 ± 3.8 kg/m(2)) and women (n = 40, BMI = 33.3 ± 4.9 kg/m(2)) during weight loss. All participants underwent a 16-week hypocaloric weight-loss program and were randomized to receive pioglitazone (30 mg/day) or no pioglitazone with or without resistance training, following a 2 × 2 factorial design. Regional body composition was measured at baseline and follow-up using computed tomography (CT). Lean mass was measured using dual X-ray absorptiometry. Men lost 6.6% and women lost 6.5% of initial body mass. The percent of fat loss varied across individual compartments. Men who were given pioglitazone lost more visceral abdominal fat than men who were not given pioglitazone (-1,160 vs. -647 cm(3), P = 0.007). Women who were given pioglitazone lost less thigh subcutaneous fat (-104 vs. -298 cm(3), P = 0.002). Pioglitazone did not affect any other outcomes. Resistance training diminished thigh muscle loss in men and women (resistance training vs. no resistance training men: -43 vs. -88 cm(3), P = 0.005; women: -34 vs. -59 cm(3), P = 0.04). In overweight/obese older men undergoing weight loss, pioglitazone increased visceral fat loss and resistance training reduced skeletal muscle loss. Additional studies are needed to clarify the observed gender differences and evaluate how these changes in body composition influence functional status.