Andrew Tarulli

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.

Electrical Impedance Myography in the Assessment of Disuse Atrophy

UNLABELLEDnTarulli AW, Duggal N, Esper GJ, Garmirian LP, Fogerson PM, Lin CH, Rutkove SB. Electrical impedance myography in the assessment of disuse atrophy.nnnOBJECTIVEnTo quantify disuse atrophy using electrical impedance myography (EIM), a noninvasive technique that we have used successfully to study neurogenic and myopathic atrophy.nnnDESIGNnWe performed EIM of the tibialis anterior of subjects with disuse atrophy secondary to cast immobilization and in their contralateral normal leg. Subjects were studied shortly after cast removal and again several weeks to months after the cast was removed and normal mobility was restored.nnnSETTINGnOutpatient neurology and orthopedic practices at a tertiary care medical center.nnnPARTICIPANTSnOtherwise healthy subjects (N=10) with unilateral leg fracture.nnnINTERVENTIONSnNot applicable.nnnMAIN OUTCOME MEASURESnResistance, reactance, and phase measured at 50kHz.nnnRESULTSnThe main EIM outcome parameter, phase at 50kHz, was lower in the immobilized leg in 9 of 10 cases. Additionally, when normal mobility was restored, the phase of the casted leg increased relative to its initial measurement in all 10 cases, while it increased inconsistently in the contralateral leg.nnnCONCLUSIONSnEIM may be a powerful tool for the assessment of disuse atrophy.

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

OBJECTIVEnTo determine the impact of skin-subcutaneous fat layer thickness on electrical impedance myography (EIM) measurements.nnnMETHODSnLinear 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.nnnRESULTSnMean 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.nnnCONCLUSIONSnSFL thickness does not contribute substantially to the phase measured by linear-EIM.nnnSIGNIFICANCEnEIM data can be interpreted confidently in individuals with varying SFL thickness.

Localized muscle impedance abnormalities in amyotrophic lateral sclerosis.

Objectives: To assess changes in electrical impedance myography (EIM) parameters in amyotrophic lateral sclerosis (ALS). Methods: Ten patients with ALS and a cohort of normal subjects underwent EIM testing of tibialis anterior. Montages using voltage and current electrodes placed at a distance (far) and in close proximity (near) were compared. The EIM parameters, resistance (R), reactance (X), and phase (&thetas;) in the patients with ALS, were compared with normal values. Results: &thetas; measured at 50 kHz using the near montage was most sensitive to the presence of ALS, with 9 of 10 patients with ALS having smaller &thetas; values than the calculated lower limit of normal. &thetas; using the far montage and X using both the near and far montages were also sensitive to disease, whereas R did not seem to be useful. Conclusion: EIM is sensitive to muscle abnormalities in ALS, with &thetas; measured with near montages providing the best results.

Electrical impedance in bovine skeletal muscle as a model for the study of neuromuscular disease

Electrical impedance myography (EIM) consists of a set of bioimpedance methods configured for neuromuscular disease assessment, in which high-frequency electrical current is applied to a limb and the consequent surface voltage pattern over a muscle is evaluated. Prior human work has shown that the EIM parameters of resistance, reactance and phase change in different neuromuscular disease states including neurogenic and myopathic conditions. These parameters are also sensitive to the angle at which current is applied and measured relative to muscle fiber direction, a characteristic known as anisotropy. In order to obtain insights into the impedance characteristics of mammalian skeletal muscle without the confounding effects of an overlying skin-fat layer, bone and irregular muscle shape, we performed EIM on three nearly ideal round 16 cm diameter, 1 cm equal thickness pieces of bovine rectus abdominis muscle. Using a standardized tetrapolar electrode array with 50 kHz electrical current, we identified strong anisotropy in the measured reactance and phase, with weaker anisotropy identified for resistance. We also found that increasing amounts of muscle maceration, a rough model of myopathic or traumatic muscle fiber injury, reduced phase and muscle anisotropy when current was injected perpendicular to the muscle fibers. These findings support that EIM parameters, including muscle anisotropy, are likely to be sensitive to the pathological changes that occur in neuromuscular disease states.

Effect of newly proposed CK reference limits on neuromuscular diagnosis

The objective was to determine the effect of a proposed increase in the upper reference limits of serum creatine kinase (CK) on neuromuscular disease diagnosis. This was a retrospective study of 94 Caucasian subjects (49 women and 45 men) in whom a neuromuscular physician ordered a CK as part of their evaluation. The patients were divided into two groups: those with diagnoses that either should or could elevate serum CK, and those with diagnoses that should not elevate serum CK. Sensitivities and specificities of the manufacturers and the newly proposed upper reference limits were determined. For women, raising the upper reference limit of CK from 140 IU/L to 201 IU/L reduced the sensitivity of the test from 50% to 29%, while increasing the specificity from 67% to 80%. For men, raising the upper reference limit of CK from 174 IU/L to 322 IU/L reduced the sensitivity from 80% to 60%, while increasing the specificity from 63% to 80%. The newly proposed upper reference limits resulted in a false‐negative CK of clinical significance in 7 of 94 subjects. Increasing the upper reference limit for CK reduced the sensitivity and increased the specificity of serum CK for neuromuscular disease diagnosis. Such a change will reduce unnecessary referrals and invasive diagnostic testing in patients with asymptomatic CK elevations. The clinical impact of the loss in sensitivity is small. If these new upper reference limits are adopted, neuromuscular physicians should be aware that a normal CK level does not exclude a diagnosis of myopathy. Muscle Nerve, 2009

The use of topiramate in refractory status epilepticus

To the Editor:nnTowne et al. reported the use of topiramate in refractory status epilepticus (SE).1 It was particularly interesting in Patient 3. Her SE was initially controlled by lorazepam, …

Reference Values for 50 kHz Electrical Impedance Myography

Electrical impedance myography (EIM) is a method for non‐invasively and quantitatively assessing muscle health, in which the major outcome parameter, phase (θ), decreases in diseased states. In order to create a set of normal reference values, we performed 50‐kHZ EIM in 5 muscles of 87 healthy individuals, using θ as the major outcome variable. Because the distributions of data were mostly skewed, logarithmic transformations were performed, and the resulting data were fitted to quadratic functions. The lower limit of normal was set by plotting the lower 95% confidence interval of the curve for each muscle and then identifying age‐specific reference values. We found that the distribution of data was similar to that for other neurophysiologic parameters. The lower limit of normal was easily defined, and relatively few values fell below the proposed lower limit. By using commercially available bioimpedance devices, these values will allow other investigators to explore the application of 50‐kHZ EIM in clinical neuromuscular disease research. Muscle Nerve, 2008

Quantifying muscle asymmetries in cervical dystonia with electrical impedance: A preliminary assessment

OBJECTIVEnCervical dystonia (CD) lacks an objective quantitative measure. Electrical impedance myography (EIM) is a non-invasive assessment method sensitive to changes in muscle structure and physiology. We evaluate the potential role of EIM in quantifying CD, hypothesizing that patients would demonstrate differences in the symmetry of muscle electrical resistance compared to controls, and that this asymmetry would decrease after botulinum neurotoxin (BoNT) treatment.nnnMETHODSnEIM was performed on the sternocleidomastoid (SCM) and cervical paraspinal (PS) muscles of CD patients and age-matched controls. 50 kHz resistance was analyzed, comparing side-to-side asymmetry in patients and controls, and, in patients, before and after BoNT treatment.nnnRESULTSnSixteen patients and 10 controls were included. Resistance asymmetry was on average 3-5 times higher in patients than controls. Receiver operating characteristic analysis demonstrated 91% accuracy of discriminating CD from normal. From pre-treatment to maximum BoNT effect, asymmetry decreased from 20.8(13.9-26.1)% to 6.2(3.1-9.9)% (SCM), and from 16.0(14.3-16.0)% to 8.4(7.0-9.2)% (PS), p<0.05 (median, interquartile range).nnnCONCLUSIONSnEIM effectively differentiates normal subjects from CD patients by revealing asymmetries in resistance values and detects improvement in muscle symmetry after treatment.nnnSIGNIFICANCEnThese results suggest that EIM, a painless, non-invasive measure, can provide a useful quantitative metric in CD evaluation and deserves further study.

Clinical utility of electrodiagnostic studies in the inpatient setting

Although nerve conduction studies/electromyograms are often requested to evaluate hospitalized patients (inpatients) with suspected neuromuscular diseases, their clinical utility has not been studied. They can be technically challenging, especially in intensive care units. We studied the contribution of inpatient electromyograms (IP‐EMGs) to the management of patients with suspected neuromuscular disorders. A total of 103 IP‐EMGs in 98 patients were analyzed. IP‐EMGs confirmed the clinical diagnosis in 53.3% and provided a new, clinically relevant diagnosis in 12.6%. IP‐EMGs revealed only an incidental diagnosis in 14.5%, were inconclusive in 16.5%, and were normal in 3%. In over a quarter of patients, IP‐EMGs assisted in planning further diagnostic evaluation or treatment. Although IP‐EMGs most often only confirm already suspected diagnoses, in a substantial minority of patients they lead to the identification of clinically unsuspected, significant diagnoses that alter subsequent clinical care. Muscle Nerve 40: 195–199, 2009