Electrical impedance myography for the assessment of children with muscular dystrophy: a preliminary study.

Electrical impedance myography (EIM) provides a non-invasive approach for quantifying the severity of neuromuscular disease. Here we determine how well EIM data correlates to functional and ultrasound (US) measures of disease in children with Duchenne muscular dystrophy (DMD) and healthy subjects. Thirteen healthy boys, aged 2-12 years and 14 boys with DMD aged 4-12 years underwent both EIM and US measurements of deltoid, biceps, wrist flexors, quadriceps, tibialis anterior, and medial gastrocnemius. EIM measurements were performed with a custom-designed probe using a commercial multifrequency bioimpedance device. US luminosity data were quantified using a gray-scale analysis approach. Children also underwent the 6-minute walk test, timed tests and strength measurements. EIM and US data were combined across muscles. EIM 50 kHz phase was able to discriminate DMD children from healthy subjects with 98% accuracy. In the DMD patients, average EIM phase measurements also correlated well with standard functional measures. For example the 50 kHz phase correlated with the Northstar Ambulatory Assessment test (R = 0.83, p = 0.02). EIM 50 kHz phase and US correlated as well, with R = -0.79 (p < 0.001). These results show that EIM provides valuable objective measures Duchenne muscular dystrophy severity.

A portable system for the assessment of neuromuscular diseases with electrical impedance myography.

PRIMARY OBJECTIVE: To create a system for the acquisition of multi-angle, multifrequency muscle impedance data. RESEARCH DESIGN: Device development and preliminary testing. METHODS AND PROCEDURES: The system presented here employs an interrogating signal composed of multiple tones with frequencies between 10 kHz and 300 kHz. The use of a composite signal makes possible measurement of impedance at multiple frequencies simultaneously. In addition, this system takes impedance measurements at multiple orientations with respect to the muscle fibres by means of an electronically reconfigurable electrode array. The required measurement time is reduced by taking advantage of muscle's linearity with respect to the flow of electrical current. MAIN OUTCOMES AND RESULTS: The system was tested in normal subjects, a patient with amyotrophic lateral sclerosis, and one with inclusion body myositis; unique impedance signatures were identified the two patients. CONCLUSIONS: Early data suggest that this system is capable of high-quality data collection and may detect changes in neuromuscular disease; study of additional normal subjects and patients with a variety of neuromuscular diseases is warranted.

Impact of skin-subcutaneous fat layer thickness on electrical impedance myography measurements: an initial assessment.

OBJECTIVE: To determine the impact of skin-subcutaneous fat layer thickness on electrical impedance myography (EIM) measurements. METHODS: Linear 50 kHz EIM was performed on quadriceps of 62 healthy subjects (mean age 52.2+/-20.6 years) with a wide variety of skin-subcutaneous fat layer (SFL) thicknesses, as measured by ultrasound. Correlations were sought between the main EIM outcome parameter phase (theta) and SFL thickness. A multiple regression analysis was also performed for theta with SFL thickness and age as independent variables. RESULTS: Mean skin-fat thickness was significantly different (p<0.01) between men (0.76+/-0.23 cm) and women (1.43+/-0.51 cm). Neither linear nor quadratic fits produced significant correlations between theta and SFL thickness. A significant but weak positive correlation (r(2)=0.14, p<0.05) was seen between age and SFL thickness in women, but not in men. A strong negative correlation between age and theta was observed for both men (r(2)=0.48, p<0.01) and women (r(2)=0.68, p<0.01). In multiple regression analysis, age but not SFL thickness was found to have a significant association with theta. CONCLUSIONS: SFL thickness does not contribute substantially to the phase measured by linear-EIM. SIGNIFICANCE: EIM data can be interpreted confidently in individuals with varying SFL thickness.

Electrical impedance myography in the bedside assessment of inflammatory myopathy.

Electrical impedance myography (EIM) is a new technique with potential for the noninvasive bedside assessment of myopathy. EIM was performed on the quadriceps of 10 patients with inflammatory myopathy and 10 normal subjects. The major EIM parameter, the spatially averaged phase, was 35% lower in the myositis patients and correlated with whole-body (r = 0.765, p = 0.01) and quadriceps (r = 0.673, p = 0.03) strength.